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ELEMENTS 



OF 



CIVIL ENGINEERING: 

BEING AN ATTEMPT TO CONSOLIDATE THE PRINCIPLES OP THE 

VARIOUS OPERATIONS 

OF THE 

CIVIL ENGINEER INTO ONE POINT OF VIEW, 



FOR THE 



AND THOSE WHO MAY BE ABOUT TO EMBARK IN THE PROFESSION. 

ILLUSTRATED BY NINE COPPERPLATES, 

CONTAINING 273 FIGURES, 
AND INTERSPERSED WITH VARIOUS USEFUL TABLES. 



BY JOHN MILLING TON I %li 

CIVIL engineer; 

William and Mary College, Va. 



PHILADELPHIA: 

J. DOBSON, CHESTNUT STREET; 

RICHMOND, VA. 

SMITH & PALMER. 

1839. 



tX 



•^ 



Entered according to the Act of Congress, in the year 1839, by Judah 
DoBsoN, in the Clerk's Office of the District Court for the Eastern District of 
Pennsylvania, 



^;. 



{ '■ 



E. G. DORSET, PRINTER, 
LIBRARY STREET. 



J 



.g jg"^" " / J^»ssf -r^imiu^- 



CONTENTS. 



J AGE. 

Preface and Dedication, - - - _ 5 

CHAPTER I. 

Introduction. — The objects of the Engineer's profession, and his necessary 

qualifications, - - - - - 9 

CHAPTER n. 

Preliminary Operations of the Engineer: 

Section I. — On the Arrangement of Plans, - - - 22 

n. — On Drawing and Drawing Implements, - 27 

CHAPTER III. 

On Mensuration, - - - - - - 71 

CHAPTER IV. 

On Land Surveying and Map Drawing, - - - 101 

CHAPTER V. 

On Levelling and Levelling Instruments, and Drawing Profiles, - 149 

CHAPTER VI. 

On Earth-work or Excavation, Canal-work, &c. - - 188 

CHAPTER VII. 
On the Construction of Roads, - . _ _ 213 

CHAPTER VIII. 

> 

On Building Materials: 

Section I. — Of Stones and Bricks, - - - 248 

n. — Of Lime, Mortar, and Cements, - - 278 

m.— Of Timber, - - - - 296 

IV.— Of Iron and other Metals, - - - 319 

A 



4 



IV CONTENTS. 



CHAPTER IX. 



On the Durability and Strength of Materials: 

Section I. — Of the Durability of Materials, - - 370 

II.— Of the Absolute Strength of Materials, - - 380 

III.— Of the Relative Strength of Materials, - 428 

CHAPTER X. 

On Construction, or Building Processes: 

Section I.— Of Stone-work, or Masonry, - - 455 

II.— Of Brick-work, - - - - 483 

III. — Of Carpentry, Roofs, Centring, &c. - - 516 

CHAPTER XL 

On Foundations and Arches: 

Section I. — Of Foundations, - - - 611 

II. — Of Stone and Brick Arches, and Bridge Building, - 634 

CHAPTER XII. 

I ractical Applications of the Foregoing Principles: 

Section I. — of Rail-roads, - - . - 671 

II. — Internal Navigation; the Improvement of Rivers; Forma- 
tion of Canals, Locks, Docks, &c. - 691 
Conclusion, - - - - - - 715 



DIRECTIONS FOR FIXING THE PLATES. 
Plate 1, to face page 66. 



2, 




134. 


3, 




186. 


4, 




360. 


5, 




490. 


6, 




536. 


7, 




570. 



8, at end of book. 

9, facing the title page. 



NOTICE 



As the plates are very long, the numbers of the figures upon them are so 
disposed, that the whole plate need not be unfolded from the book when first 
beginning to refer to it. 



PREFACE AND DEDICATION. 



The subject of Civil Engineering is one upon which much has 
been written by some of the first scientific characters of the 
world; but their writings are so diffuse, so various, and so de- 
tached on account of their investigations having been directed to 
particular objects, that there is perhaps no branch of science in 
which the student or young beginner finds so much difficulty in 
obtaining the knowledge necessary to qualify him for his busi- 
ness, as in Civil Engineering. Among the almost numberless 
works which the presses of Great Britain and France issue an- 
nually, it is surprising that no attempt has yet been made (to the 
knowledge of the writer) at any thing like a compendium of the 
science of Engineering. The English nation is even avowedly 
poor in practical works of this description, for until the forma- 
tion of the Society of Civil Engineers, of London, and the 
more recent establishment of the Institute of Civil Engineers, 
the persons who followed the profession appeared to harbour a 
jealous suspicion of their modes of operating and proceeding 
meeting the public eye; and with the exception of Smeaton's ac- 
count of the building of the Eddystone Light-house, and that of 
the building of Essex Bridge, in Dublin, there was scarcely a 
work of any importance to be found in the English language. 
Even the papers of Smeaton would, for want of being known, 
probably have been buried in oblivion on the shelves of some 
public library, had not the late Sir Joseph Banks and others, into 
whose hands they fell, found them too valuable to be withheld 
from the public; and therefore caused them to be published after 
the death of this justly celebrated man, the father of the Civil 
Engineering profession. He was followed by Brindley, Jessup, 
Mylne, Walker, Rennie, Alexander, and several others, who 
were entrusted with all the great and magnificent works that 
have been executed in Great Britain; but if we look for any de- 
tailed or particular account of their operations, our search must 
be in vain, for nothing of their proceedings has ever been given 
to the public. The French, on the contrary^, have been much 
more liberal in their publications, but their works are confined 



VI PREFACE AND DEDICATION. 

either to scientific investigations or to the account of particular 
objects, diffused through many large and expensive volumes, so 
that a student in Civil Engineering had no chance of knowing 
what had been done on the continent of Europe without access 
to a large public library; and even if he possessed that advantage 
it was perhaps useless to him, from not understanding the lan- 
guage the works were written in, or more especially from his 
possessing no key or directory to inform him where he should 
search for particular information. Thus circumstanced, the young 
Engineer had no chance of improving himself, except by his own 
practical means and observation, aided by the information he 
might obtain from his master, if employed in the office of an 
Engineer, and yet such was the state of the profession when the 
writer embarked in it. 

The French nation, during the short period of tranquillity 
which succeeded the accession of Napoleon Bonaparte to the 
government of that country, were the first who awakened to the 
necessity of cultivating Civil Engineering as a means of national 
improvement, by public education; and the two great national 
schools then established, L'Ecole Polytechnique or College of 
Practical Arts and Manufactures, and the Corps des Fonts et 
Chauss6es, or Publicly instructed Body of Bridge Builders and 
Road Makers, contributed in no small degree to the advancement 
of the profession and the improvement of the country; for the 
instruction afforded by these great institutions was not confined to 
the mere objects of their titles but extended to all branches of the 
Engineer's profession. The first attempt at any thing like instruc- 
tion in the Engineering profession that was made in England, 
was on the establishment of the London University; and in 1828 
the writer had the honour of being appointed to the chair of Civil 
Engineering and the Applications of the Principles of Mechanical 
and Chemical Science to the Arts and Manufactures; and it was 
in the preparation for the lectures to be given on these subjects, 
that he first felt the want of a Digest or Text Book, that should 
condense and bring the whole subject matter of his courses before 
the student. He searched and searched in vain for such a book, 
and it was therefore determined that he should endeavour to pro- 
duce one which was to have been published under the auspices of 
the Society for the Diffusion of Useful Knowledge, and some 
progress was made in the undertaking. But being called upon to 
undertake the Engineering superintendence of one of the Great 
English Silver Mining Company's concerns in Mexico, he was 
induced to resign his professorship, and with it, his intended 
work, and after leaving England thought no more on the sub- 
ject. 



PREFACE AND DEDICATION. Vll 

Early in 1836, being then Professor of Natural Philosophy and 
Chemistry in the venerable establishment of William and Mary 
College, Va., he was requested by the visitors of that institution 
to attempt a course of Civil Engineering, as a branch of the col- 
legiate instruction; and although but ill prepared at that time for 
such an undertaking, being wholly without drawings, models, 
books of reference, and other means of illustration, he undertook 
it, using a translation of the elementary course on Civil Engineer- 
ing by M. J. Sganzin, written many years ago, and intended by 
its author to be a mere syllabus or collection of memoranda from 
the course on these subjects, that he formerly delivered at the 
Polytechnic School in Paris. Those who are acquainted with 
this book need not be told how meagre and insufficient it is for 
an Engineer of the present day, independent of which, the lan- 
guage into which it is translated is so full of French words and 
phraseology, not adopted in this country, as to render it almost 
unintelligible. Under these circumstances such a book could but 
be discarded, and in the course of the succeeding session, 1837-8, 
the writer was under the necessity of preparing a set of notes of 
his own to lecture from, and these notes, so prepared and some- 
what amplified to make them intelligible to a reader, are what 
are now ofiered to the public in the following pages. 

The writer (for he has in no case assumed the title of author, 
feeling that he was not fully entitled to that name, when the 
matter he was inculcating did not originate with himself) in pre- 
paring these notes has been careful to select whatever he thought 
might be most useful to the young Engineer, and on this account 
he has availed himself of all information that fell within his reach. 
Not, however, exactly in the shape of compilation or extracts 
from other books, because unfortunately he did not possess them, 
and he has therefore, in many instances, been compelled to resort 
to his memory when he would have preferred giving extracts. 
There are subjects on which few Engineers have the means or 
opportunity of making experiments, such as those on the strength 
and resistance of materials; and in such cases he has borrowed 
freely from Professor Robison, Dr. Young, Tredgold, and such 
writers as are deemed most worthy of confidence. But when 
such extracts have been made he has, in every case, cited the 
authority; but, with the exception of those extracts, the whole 
has been written in such manner as to blend the result of his own 
experience and observation with what is generally taught and 
understood upon the subjects; and much matter will be found 
which, he believes, has not before appeared in print. 

The course he has adopted, is first to explain the nature of the 
Engineer's profession, and the views that ought to guide him in 



Vlll PREFACE AND DEDICATION. 

the formation of his plans. 2ndly. The means of rendering those 
plans palpable by means of drawings, the method of making and 
copying which, and the necessary instruments, are briefly de- 
scribed, and as the value of all building work depends in great 
measure upon its quantity, so the means of ascertaining those 
quantities by measurement are next considered. 

Possessing this preliminary knowledge, the young Engineer is 
next supposed to be introduced into an uncultivated country, 
which he has to improve by carrying his plans into execution; 
and the first object will be to measure, and make maps of such 
country, upon which he may lay down the roads, canals, and other 
improvements that are contemplated. So much of land survey- 
ing and levelling and their necessary instruments, are therefore 
described in the fourth and fifth chapters as will enable him to 
accomplish this work. 

The sixth chapter treats of such operations on the soil as are 
necessary for the formation of roads, canals, and the foundations 
of buildings; and this is followed in the seventh chapter by the 
leading principles of road making. 

The selection of materials to work with, comes next under 
consideration; and the eighth chapter therefore describes the va- 
rious kinds of building stones, and the methods of quarrying, or 
getting them out of the earth, which is followed by an account of 
the making of bricks, burning and preparing lime and hydraulic 
cements, and forming them into mortar. Secondly, the varieties 
of timber, and means of seasoning, and converting it to useful 
purposes, and of measuring and valuing it, either when rough or 
converted, are considered. Lastly, the metals claim attention, 
and an account is given of the production of iron from its ore, 
and its conversion into the pig and malleable state. This is fol- 
lowed by such a notice of the smithing and iron foundry business 
as the Engineer should be generally acquainted with, particularly 
the making of patterns to cast from. A few observations on 
steel, brass, copper, lead, and the other metals in general use, are 
added, and close this part of the subject. 

The Engineer being thus put in possession of a catalogue of the 
materials he has to work with, must next consider their respective 
values and importance under the heads of strength and durability, 
which subjects occupy the ninth chapter. 

Construction, or the conversion of these materials (now sup- 
posed to be fully understood) next follows, and is treated of in 
the tenth chapter, under the several heads of building with stone 
and bricks, and carpentry or building in wood. The principles 
of building both in stone and bricks, are here described, together 
with the methods of measuring and valuing the work when exe- 



PREFACE AND DEDICATION. IX 

cuted. Carpentry follows, and after an account of the principles 
on which this art depends, those principles are applied to the 
formation of various kinds of framing, such as roofs, partitions, 
timber bridges, and the centring or frame work necessary for the 
formation of large arches of stone or bricks, and some of the most 
approved centres that have been used are described. 

The eleventh chapter is devoted to the methods of procuring 
firm and stable foundations, both on dry land and in the water, 
for walls and heavy erections; and this, of course, includes the 
building of piers for bridges, and the usual methods of building 
in water both by coffer-dams and caissoons, the driving of piles, 
the fixing of centring, and the construction of large arches, and 
building of bridges; which subjects are exemplified by a short 
account of some of the finest stone and cast iron bridges that have 
been executed, and a notice of the more recently introduced 
bridges of suspension. 

As the foregoing matter comprises most of the information that 
it is necessary the young Engineer should possess, all that re- 
mains is to point out how the principles endeavoured to be esta- 
blished are to be applied to useful purposes; and this opens an 
almost endless field on account of the many ramifications of the 
Engineer's profession. Any attempt to describe the whole, or 
even the greater part of them in such manner as might prove 
useful, would require a work of vast extent and high price, and 
might not, after all, prove generally useful or acceptable; because 
no individual scarcely ever attempts to make himself practically 
acquainted with the whole of them. On this account the twelfth 
chapter is confined to a description of those operations which the 
Civil Engineer is most commonly called upon to design, super- 
intend, and execute; and these are the formation of roads and rail- 
roads, the improvement of river navigation, and the construction 
of navigable canals. In this place, therefore, the form, construc- 
tion, and methods of fixing rails, and of building locks and weirs, 
are alone set forth; because the necessary appendages of walls, 
bridges, foundations, warehouses, carpentry, and earth- work, have 
been fully discussed and described in preceding chapters. It is 
therefore presumed that the directions given throughout the work, 
when combined with some practice, which is indispensable to 
form a good Engineer, will enable any one to digest and arrange 
plans; to draw them upon paper; to estimate their probable cost; 
to set them out upon the ground; and to direct and superintend 
their construction: and if they should be found to answer that 
purpose, or even to assist in its accomplishment, the object of the 
writer will be fully attained. 

The work was written and compiled at detached periods, as the 



X PREFACE AND DEDICATION. 

matter was required for the lectures of the writer; and having 
been printed in Philadelphia, many miles from his residence, the 
presswork has not received that vigilant attention to its correction 
that he was desirous of bestowing upon it; and he therefore fears 
many errors will be discovered; but he trusts none that will 
affect the sense. With these, and all its other imperfections, he 
sends it forth, relying on the indulgence of the public to excuse 
the omissions and inaccuracies that ever attend a first attempt to 
produce and condense into a single volume, so large a body of 
practical information, and he 

DEDICATES 

it to the patronage of the rising generation of Civil Engineers, 
from a conviction, that although the book does not profess to 
contain anything like the whole of the knowledge that an Engi- 
neer ought to possess, yet it contains nothing but what every 
young Engineer should be acquainted with; and he therefore 
trusts it may prove useful to them. 

If the health and leisure of the writer should permit, he pro- 
poses, at some future time, to publish another volume, unconnect- 
ed with the present one, which shall contain the result of his 
own experience, embodied with the most material observations 
of the best writers on the construction of mill-work and machinery, 
and particularly of the steam-engine; on the construction of 
water-works for supplying towns with water; and on mining 
operations, in all of which he has been extensively and practically 
engaged. 

William and Mary College^ ") 
Williamsburg, Fa., March, 1839. $ 



ELEMENTS 



OP 



CIVIL ENGINEERING 



CHAPTER I. 



INTRODUCTION.- OF THE OBJECTS OF THE ENGINEER'S PROFESSTON.—THE 
EDUCATION AND QUALIFICATIONS OF AN ENGINEER. 

The word engine is used in mechanics to express a compound 
machine, constituted of one or more mechanical powers, such as 
levers, pullies, screws, and the like, so put together and arranged 
as to produce an effect which could not be brought about without 
them; and a person capable of devising or contriving, and con- 
structing such a machine, or, in some cases, of using it to the 
greatest advantage when constructed, is called an Engineer. 
Machines, or engines, are constructed by workmen, in their seve- 
ral departments, according to the materials made use of, such as 
carpenters, joiners, millwrights, blacksmiths, founders, turners, 
and the like; but men constantly occupied in the daily labour of 
such avocations cannot be expected to have the necessary time 
for studying the philosophical principles of the operations they 
are constantly performing; and hence, although such men will 
by constant habit and practice become able, expert, and frequently 
rapid workmen, and will improve their own tools and processes 
of operation, yet we seldom find them aiming at any thing new 
or original. They constantly require long explanations, or draw- 
ings, or models of the things they have to construct, placed before 
2 



10 INTRODUCTION. 

them; and occasionally the object itself must be within their 
inspection, in order to enable them to copy it, or contrive what 
is required. It is only in a very few instances that we meet with 
bright flights of genius and invention of new machines arising 
from workmen who are constantly tied down to their daily occu- 
pations. This arises from several causes: the first and most im- 
portant of which is the constant and unremitting attention they 
are compelled to give to their business in order to gain a com- 
fortable subsistence; secondly, their almost constant confinement 
to their workshops, where the same kind of occupation is daily 
going on; so that they have little or no opportunity of seeing 
a variety of operations, or of knowing what is doing without 
their walls, and what already exists, or has yet to be invented 
and discovered; and lastly, the small opportunities they have for 
improving their minds, or learning the scientific principles that 
apply, even perhaps to the very business in which they are con- 
stantly occupied: for few men feel an inclination to read or study 
in the evening after a day of hard labour.* 

* This difficulty, in the way of acquiring knowledge among the working 
classes of society, was in a great measure obviated in London by the establish- 
ment of the London Mechanics' Institution, of which the author had the honour 
of being one of the founders and first vice-presidents. Its beneficial influence 
was soon felt, and many similar societies soon arose out of it, in different parts 
of the kingdom, as well as in foreign countries. Working men seldom purchase 
books, and do not in general like to sit down to reading when the labour of 
the day is over; but they are always ready to attend a lecture for an hour in the 
evening, and to listen to good and useful instruction, provided it is given to them 
in a plain, simple, and intelligible form. The truth of this position is amply 
proved by the progress of the London Mechanics' Institution, which had not 
been long opened before it was joined by 1200 of the working artizans of Lon- 
don, who came to it voluntarily and without persuasion. The numbers being 
large, the expense was small. Each member paid an admission fee of 62 1 
cents, and an annual contribution of $1 50. The sons and apprentices of mem- 
bers were admitted at the rate of 62 5 cents per annum, their parents or guardians 
entering into bond for their good and orderly conduct. Small as this sum may 
appear, it enabled the society to purchase and alter a large house into a lecture 
room, capable of holding between seven and eight liundred persons, and to fit 
up a library and chemical laboratory, which were well stocked with books and 
apparatus. In this place a plain and simple lecture, connected with science or 
the useful arts, was delivered every evening at eight o'clock, and the books of 
the library were circulated among the members. All political and religious sub- 
jects were excluded from discussion; and the author, from his own experience, 
can assert, that during the several years that he was connected with the insti- 
tution, a better conducted, orderly, and more inquiring audience, never assembled 
in any public place. Hundreds, who would have spent their evenings and 
money in taverns and public houses, were thus quietly enticed away and gradu- 
ally instructed in the rudiments of science and morality, without any trouble 
to themselves, and their minds and habits ameliorated at the same time. The 
lectures were in general gratuitously delivered by the friends and patrons of the 
society. 



INTRODUCTION. 11 

With the Engineer the case is quite different, since he is not 
expected to be a workman, although it will be more to his ad- 
vantage, and that of his employer, and of his workmen also, if he 
is one, although he may not practise his art; because it is his duty 
to invent and devise machinery, to select materials, and to direct 
and superintend his workmen; and no one can do this so fully 
and eflfectually, or can be so good a judge of the performance of 
a piece of work, or the difficulties attending its execution and the 
time necessary for overcoming them, as one who could work and 
make the thing himself, in case of the necessity of his doing so. 
Indeed the Civil Engineer is often thrown into situations in pur- 
suing his profession, where, from thinness of population and the 
consequent deficiency of mechanical establishments, he can get 
nothing made for him; and when so situated, that man will always 
feel his superiority and independence if he can take up an axe or 
saw, or even a pocket-knife, and fashion out something like what 
he wants, either to answer his purpose, or to enable a country 
blacksmith or carpenter to make him a better article, which they 
can generally do if they have a model to work from, though it 
might be impossible to make them understand a drav^^ing or oral 
description. 

It is not exactly known when the name Engineer was first made 
use of, but in its more ancient signification it had constant refer- 
ence to military affairs, and was so used in this country and in 
Europe until very near the close of the last century, when we 
find the term Civil Engineer first adopted to distinguish it from 
the other class of engineers, now constantly styled Military En- 
gineers. 

The operations to be performed by these two classes of En- 
gineers are to a certain extent similar, consequently the course 
of education to be pursued by them will in most respects be the 
same. But, inasmuch as the occupations of the Civil Engineer are 
more general and extended than those of the Military Engineer, 
so it is necessary that his knowledge should also be more general 
and extended, as will be seen by taking a cursory view of the 
duties that these two classes of men are usually called upon to 
perform, and the manner of executing them. 

Military engineering is found of such vast use and importance 
to every army, that no civilized and well organized nation is now 
without its corps of engineers, who exist as a body, separate and 
detached from the general army; and a portion is always selected 
out from this body to accompany every army that goes into the 
field. The officers commanding in the engineer corps are re- 
quired to be qualified for their duties by an appropriate education 



12 INTRODUCTION. 

in Colleges, usually established by the governments under which 
they are to serve, and which are placed within their immediate 
surveillance; and here they are instructed in mathematics, draw- 
ing, fortification, chemistry, the arts and arrangements of war, 
both defensive and offensive, and in such mechanical arts as they 
may be called upon to perform, in addition to the usual duties of 
a military life; and no man is deemed eligible to serve as an en- 
gineer officer until he has passed his examination and received 
his certificate of competency from such a college. The men, or 
privates, that are placed under these officers, are in like manner 
instructed by them as far as necessary, and the majority of them 
are artizans of some description, as well as soldiers. They con- 
sist of carpenters, blacksmiths, masons, earth w^orkmen, timber- 
men, and other mechanics; and as a corps of engineers never 
moves without its portable smith's forges, saws, axes, shovels, 
pick-axes, and various other tools, it will be seen at once that it 
constitutes the mathematical and mechanical branch of the army, 
and will be capable of performing many operations of the highest 
importance to the success of an expedition, which ordinary officers 
and men could not perform, being deficient not only in the skill, 
but in the necessary means of carrying them into execution. 

If an expedition is ordered against an unknown place, the 
Engineers must precede. It is their duty to investigate the road 
or mode of approach, to find out the best one, to render it avail- 
able for the passage not only of the soldiers, but of heavy artillery, 
baggage and provisions; and if no such road exists, to form it. 
A temporary bridge may be necessary for the passage of a river 
— it is their duty to construct it; and, if occasion requires, to 
throw up redoubts or batteries, and place guns upon them for the 
protection of the army as it advances. Having reached the place 
of attack, they have to reconnoitre, and, if possible, to find out 
the weakest place for attack; and as they can seldom approach the 
immediate vicinity of their object of research, they must have 
recourse to trigonometrical operations in order to determine the 
distance and bearings of what they have to examine. The digging 
out of entrenchments for the protection of the army; the forma- 
tion and throwing up of batteries; the computation of the proper 
quantity of powder to carry the balls or shells to the distances 
they have computed; the placing the guns upon such batteries; 
and many other duties of a similar nature, all having depen- 
dence on mathematical knowledge and mechanical skill, devolve 
upon the Military Engineer. Having thus assisted in getting his 
party to the proposed point, his next care must be to provide for 
its retreat in the event of its being overpowered; and to prepare 
such roads, bridges, batteries, and other works, as may be neces- 



INTRODUCTION. 13 

sary for this purpose; and not only to prepare^ but to destroy 
them as soon as they have answered their intended purpose, in 
order that they may become unavailable to a pursuing enemy. 
The operations of a Military Engineer are consequently of a tem- 
porary nature, but they require a concentration of talent and of 
energy to enable him to avail of every facility that may present 
itself. Their work, from the haste in which it is accomplished, 
and the scant}^ means often afforded of carrying it into execution, 
is not calculated to endure; nor should it be so, for that which is 
constructed to-day may all have to be taken down and levelled 
on the morrow; iDut still it must be strong enough to answer its 
intended purpose: and when it is considered that all these opera- 
tions have to be carried on in the face of an enemy, and under 
constant exposure to danger, it must be confessed the service is 
an arduous one, and one that requires no ordinary talent for its 
fulfilment. The skill and exertions of the Military Engineer are 
not only required in time of war, but in that of peace also; for in 
the latter period, the care and repairs of all forts and establish- 
ments for the security of a country against invasion, and the 
construction of such new ones as may be thought necessary, de- 
volve upon him. And of late years the wholesome expedient of 
employing a part of the engineer corps in making minute topo- 
graphical surveys of the countries to which they belong, has been 
resorted to. This at once puts us in possession of better, more 
accurate, and at the same time more detailed maps of the country 
than could otherwise be produced, and affords interesting employ- 
ment and pay to a most valuable profession, vs^hich would other- 
wise be useless and inactive; at the same time that it affords prac- 
tice, and renders the parties more skilful in the surveys and ope- 
rations they may be called upon to joerform in the pursuit of their 
immediate duties. 

With the Civil Engineer the case is quite different; he may be 
called upon to make surveys, to construct roads, to build bridges, 
and to perform many duties similar to those of the military en- 
gineer; but they are done in a very different manner. There is 
no danger in his surveys, or opposition to his plans. He has 
time to consider and to mature all he undertakes. He has facili- 
ties afforded him for obtaining his materials; he has money at 
his command, and can select the best of workmen. He is not 
working in the midst of enemies, but every one is trying to assist 
him. His works are not of a temporary nature, designed to be 
pulled down and destroyed as soon as they are finished, but they 
are durable. He works not for the occasion of the moment, but 
his aim should be to work for posterity; and, if possible, to make 
his constructions everlasting. To do this, every aid of science 



14 INTRODUCTION. 

must be put in requisition. He must become acquainted with 
the materials he has to work with, and not only with their me- 
chanical properties of cohesion and solidity, by which they resist 
fracture, but their chemical properties, which render them more 
or less liable to decomposition and decay. He must understand 
the mechanical powers that will enable him to raise vast masses 
to great heights, that he may be able to put his construction to- 
gether. He must understand the laws by which such bodies will 
press and operate upon each other, which can only be ascertain- 
ed by mathematics; and upon this also, he must rely for deter- 
mining the best means of putting the parts together and fixing 
them. His observations are, likewise, not confined to the making 
of roads and excavations and embankments; but he will occasion- 
ally have to combat the power of the elements in every shape. 
The merciless wave, the expansive power of steam, the raging 
tempest, and the sweeping torrent are his foes, and he must have 
them all under his control; for it may become his duty to place 
constructions that shall, in turn, resist them all. In fact, the 
versatility of his occupations is such, that it seldom happens that 
any one man can attend to them all; and thus it happens that the 
profession becomes divided into a number of branches, and each 
man takes up that portion which is most congenial to his own 
views and ability; and by this division of labour and talent, 
greater perfection is insured to the public. Thus one man may 
confine his attention to under-ground operations in the work- 
ing of metallic mines, or mines of coal; and by so doing he be- 
comes more intimately acquainted with the geological construc- 
tion of the crust of the earth, and the means of raising large 
quantities of water from great depths, than him who confines his 
operations to the surface alone. Another may choose to turn his 
attention to the construction of powerful steam engines, and the 
formation of machinery for manufacturing purposes. A third 
may confine himself to earth-work, or the formation of roads and 
canals, and the improvement of natural rivers; while a fourth 
may prefer the building art, and the erection of bridges, harbours, 
lighthouses, or manufactories. All these, however, are but parts 
of the general business of an Engineer, and to be perfect in his 
profession he should possess a general knowledge of the whole 
of them, notwithstanding he may only practise a part. By ju- 
diciously selecting a part, and pursuing it with steadfast zeal, he 
cannot fail of arriving at perfection in that department; and the 
public readily find out those men that excel most in particular 
departments, and never fail to give them due encouragement. 

From the above short statement of the nature of tlie occupa- 
tions of the Civil Engineer, it may appear that they coincide in 



INTRODUCTION. 15 

many particulars with that of the architect, and this to a certain 
extent is true; and until lately there was a difficulty in drawing 
the line of demarcation or separation between the two professions. 
Formerly the Civil Engineer was unknown, and, therefore, all 
devolved on the Architect, as may be seen by referring to the 
works of Marcus Pollio Vitruvius, a very distinguished Roman 
writer on architecture, whose date and birth-place are not exactly 
known, further than that he was inspector of military engines 
under the Emperor Augustus. His manuscript work was dis- 
covered in the fifteenth century, and has ever since been held in 
high estimation.* He declares himself to be a practising archi- 
tect, and he distributes his work into ten books, in which are de- 
scribed, not only every thing that relates to buildings, public and 
private, their site, materials, forms, ornaments and conveniences, 
but all that was then known and practised in civil and military 
engineering; giving detailed accounts of pumps, water engines, 
mechanical machines, and all the implements of war. Besides 
the instruction to be derived from this work, it has afforded 
much important matter to the antiquary relative to the state of 
arts and sciences, as well as the details of private life, among the 
Romans. From the post he held, and the description he gives of 
the nature of warfare and warlike engines, we obtain evidence 
that at this period the professions of Civil and Military Engineer 
were conjoined in one person. 

As the progress of civilization in society advances, we find the 
divisions of talent and labour increase, and accordingly the Archi- 
tect and Engineer now rank as distinct professions. The Archi- 
tect takes upon himself the construction of all public and pri- 
vate edifices, such as churches, palaces, theatres, public halls 
or institutions, and private dwellings, and does not concern him- 
self with making the roads that are to lead to them, the canals 
and navigationsthat are to convey his materials, or the machinery 
that may be necessary to convert them, or raise them to their 
places. All this is done for him by the Engineer, who, in addi- 
tion to these duties, appropriates to himself the designing and 
formation of such things as are necessary to the inhabitants, who 
are to take possession of what the Architect finishes. The En- 
gineer has to construct mills for grinding corn, and machinery 
for manufacturing those things which are necessary to the com- 
forts or luxury of the public. He supplies their towns with 

*A good translation of his works into English, accompanied by many plates, 
was produced by Mr. Newton of London, 1791; and a magnificent edition of 
that part which relates to civil architecture has since been published in London 
by W. Wilkins, Jr., A. M., F. R. S., &c. 



16 INTRODUCTION. 

water. He constructs the apparatus for lighting them with- gas. 
He supplies them with the means of extinguishing fires; and, in 
fact, renders himself useful in numberless ways. 

Notwithstanding this division, there are some points in which 
the two professions have common objects. Thus the construc- 
tions of the one and the other require the protection of a roof, 
and the formation of floors and partitions; and whenever these 
are large, they cannot be made with any certainty of stability and 
duration without a knowledge of scientific carpentry. The con- 
struction of bridges is another object which is claimed by both pro- 
fessions, and it does not appear to have been distinctly deter- 
mined to which they belong, for they have been executed in an 
equally satisfactory manner by both. Of late years the prac- 
tice in England has been to entrust the construction of large 
bridges to Engineers alone; and this is, perhaps, the safest prin- 
ciple, if the Engineer is well grounded in the scientific principles 
of his profession; because a well educated Engineer should be ac- 
quainted with every thing that relates to architecture, although 
it is not equally necessary that the Architect should be versed 
in all that relates to the engineering profession. Some persons 
are inclined to treat architecture only as a branch of the polite arts, 
and imagine that all that is necessary to constitute an Architect is, 
that he need only be a good and tasteful draughtsman, capable of 
producing an elegant design that shall gratify the eye, embellish 
the place of its erection, and be replete with every accommoda- 
tion for the purposes for which it is intended. This is, however, 
a mistaken notion, for no Architect is worthy to be called by that 
name, however splendid the designs he may produce, unless he 
is able to carry the whole into execution in the most minute de- 
tails. The very derivation of the word, ^/>;tof -rs^rav, implies this 
power; and without it, and mental conception of the means of 
execution, he might produce designs that might appear perfect 
and admirable, but which could not jDOSsibly be carried into ef- 
fect, in consequence of their not being founded on the sound 
principles of construction. On the contrary, being in possession 
of such principles, he proceeds boldly with his work, and may, in 
some instances, produce that which, to the untaught, may appear 
frightfully deficient in stability, but which he knows will be 
strong and durable. That accomplished and scientific Architect, 
Sir Christopher Wren, gave an instance of this in a design that 
he made for a spire for one of the churches in London. It was 
a tall polygonal pyramid of stone, rising to a great height, and 
supported below upon flying buttresses, with large open spaces 
between them, so as to give it almost the appearance of being de- 
tached from the building below, and having such an air of insta- 



INTRODUCTION. 17 

bility that, notwithstanding the elegance of its form, the corpo- 
ration would not permit its erection, from a fear that the slight- 
est gale of wind would bring it down. Wren being satisfied of 
its stability, became the more anxious to carry it into execution, 
and at length got permission to execute it; and it was built ac- 
cordingly, and has stood the test of upwards of a hundred years, 
without the least symptom of failure or decay; and is considered 
by all competent judges, as one of the most splendid efforts of 
architectural genius, and greatest ornaments of London. There 
is one distinctive difference between the two professions — an 
Architect must, of necessity, be a man of taste in design, while 
the Engineer must be a practical mechanic; for without these 
qualifications, they would neither of them be able to pursue their 
respective professions. But taste and elegance, although desira- 
ble qualifications, are not so much looked for in the Engineer, as 
strength, stability, and perfection of workmanship. The two 
professions can, therefore, and do very frequently go hand in 
hand, particularly in the construction of large bridges, where the 
Architect may be called upon to design, and the Engineer to exe- 
cute at least the pile-driving, pumping, and primitive opera- 
tions, if not to complete the whole structure. 

From this account it will appear that a very considerable 
acquirement of knowledge is necessary, in common to the Archi- 
tect and the Engineer, before they can become perfect in their 
several callings; and parts of this knowledge require considerable 
assiduity and application for its attainment. They should be pro- 
foundly skilled in the knowledge of the properties of the mate- 
rials to be employed, and the best methods of connecting them 
together; and to attain this, some knowledge of chemistry is ne- 
cessary. They must know so much of mathematics as relates to 
gravitation, the composition and resolution of forces, and the 
properties of the lever and inclined plane, before they can ascer- 
tain the stability of their works, and the pressure that one mass 
may exert against another; and this leads to the theory of the 
pressure and equilibrium of arches and formation of piers for 
bridges. A knowledge of mensuration is essential for measuring 
and estimating the various w^ork performed by artificers, and this 
implies a previous acquaintance with arithmetic and geometry, 
which is useful in manj^ other respects, for circles, ellipses, para- 
bolas, hyperbolas, and many other curves, which occur in the 
formation of arches and mouldings; and polygons are necessary 
in a variety of instances. They should not be unacquainted with 
plain trigonometry, for this is necessary in obtaining heights and 
distances, as well as in surveying land and setting out roads and 
canals. They must understand drawing, both in simple projec- 



18 INTRODUCTION. 

tion and perspective, to enable them to lay down designs, and 
make them plain and perspicuous to their workmen. They 
should understand so much of the law, as will enable them to 
decide upon the rights and the division of property, to inform 
themselves of the restrictions under which they have to work, 
and to make binding contracts or agreements with their work- 
men and suppliers of materials. They have, in great measure, 
a new language to learn, for all businesses have technical names 
and phrases, by means of which, alone, they can convey clear 
ideas to executive workmen; and they should be clear in judg- 
ment, ready in invention, and strict and diligent in their duties; 
for they are always considered responsible for the mistakes, 
negligence, and ignorance of those they may employ. An Archi- 
tect, or Engineer, is an intermediate agent between the employer 
and the mechanic; they should, therefore, study the honour and 
interest of the former, while they defend the rights of the latter, 
by seeing that just and equitable prices are allowed for all that is 
done, and that no overcharges or impositions are allowed to be 
made. That no bad or inferior materials are permitted to be used; 
that contractors act up to the letter of their contracts, and per- 
form all that they have undertaken to do; that workmen are only 
paid for the actual hours of their employment; and, in fact, that 
perfect justice is reciprocally rendered by the employers and the 
employed. 

As Engineers and Architects, of established reputation, have 
generally a number of large works proceeding at the sam^e time, 
it is quite impossible that they can personally attend to all the 
particulars above enumerated, and many otliers that occur. It 
is, therefore, customary, in all large works, to appoint a Clerk of 
the works, or resident engineer, whose duty is to give no direc- 
tions of his own, but to act strictly under the orders and direc- 
tions of the principal; and to watch that all his arrangements are 
punctually complied with. He must live constantly on the spot 
where the work is proceeding; must call the roll of workmen, 
and note down such as are not punctual in their attendance; must 
measure their work as it proceeds; and keep a correct account, 
by weight or measure, as the case may require, of all m.aterials 
that are delivered for the use of the works, as well as of the 
quantities consumed in its progress; and all these he must report 
to his principal, at stated periods. He has care and custody of 
the plans and drawings, and sets out the work, or gives such di- 
rections as from time to time may be necessary, during the ab- 
sence of his employer; but in cases of doubt or difficulty, should 
wait his arrival and advice, unless they are of such extreme exi- 
gency as not to permit of delay. The post of clerk of the works. 



INTRODUCTIOX. 19 

is the one that young men usually occupy on their first entry into 
the }3rofession; but they ought not even to enter upon this, with- 
out some time previously spent in the office of an Engineer, or 
Architect, that they may acquire some knowledge of drawing, of 
the computations of measurement, the mode of keeping work- 
men's time and accounts, and many other minutiae which can- 
not be so well acquired in any other way. If they have not this 
advantage it is hoped that the following sheets will, in some mea- 
sure, supply its place, by diligently studying and working the 
rules and examples given. No scliool is, however, so good for 
learning the practice of architectural or engineering business, as 
the office of clerk of the works, if entered upon with sufficient 
qualifications and properly made use of for that purpose. In this 
post, a man is constantly surrounded by work and workmen; he 
acquires their technical language without study; he sees opera- 
tions of every kind going on at the same time, and becomes ac- 
quainted with the tools and the methods of using them; he has 
the inspection and examination of various materials, and becomes 
acquainted with their respective advantages, disadvantages, and 
their prices, without leaving home. He learns to judge what 
quantity of work a man is capable of effecting in a given time, 
and acquires a fund of information that will prove of vast use to 
him in after life; for no one need expect to become a good and 
efficient Engineer by study in his closet alone, however intense. 
He must be practically a workman, or must become intimately 
acquainted with the processes of working, by watching those 
who are proficients, and this is, therefore, a mode of instruction 
which every young man ought to avail himself of, if he intends to 
excel; for in afterlife, when he becomes settled in his profession, 
he will find that he seldom has leisure or inclination to acquire 
this kind of instruction. 

The term Civil Engineer, that has been adopted by those whose 
profession it is to execute the internal improvements of the coun- 
try, in contradistinction to Military Engnieers, is of late origin, 
and does not appear to have been known in England until about 
1760. In 1771 a Society was first established in London, under 
the title of the Society of Civil Engineers, and its origin is thus 
given in the preface to the quarto edition of the reports and works 
of Mr. John Sraeaton, one of the most eminent Engineers that 
England has produced, and whose valuable papers were printed 
and published by that Society after Mr. Smeaton's death, because 
he had been one of the most distinguished ornaments of the so- 
ciety while living. The account states that the Society of Civil 
Engineers took its rise about the period above mentioned, when 
a new era in all the arts and sciences, learned and polite, com- 



20 INTRODUCTION- 

menced in England. Every thing that could contribute to the 
comfort, the beauty and prosperity of the country, moved for- 
ward in improvement so rapidly, and so obviously, as to mark 
that period with particular distinction. The learned societies 
extended their views, labours, and objects of research. The 
professors of the polite arts associated together for the first time 
under the sanction and protection of the throne. Military and 
naval establishments were made or enlarged, the manufactures 
were extended on a new plan by the enterprise, the capital, and, 
above all, the science of men of deep knowledge and persevering 
industry; and it was then first perceived that it would be better 
for establishments to be set down on new situations, best suited 
for raw materials and the labour of patient and retiring industry, 
than to be plagued with the miserable little politics of corporate 
towns, and the wages of their extravagant workmen. 

This produced a new demand not thought of till then in the 
country — internal navigation. To make communications from 
factory to factory, and from warehouses to harbours, as w^ell as 
to carry raw materials to and from such establishments, became 
absolutely necessary: hence arose those wonderful works, not of 
pompous and useless magnificence, but of real utility, which had 
the effect of rendering Great Britain pre-eminent as a manufac- 
turing country, in a period of time much shorter than its fondest 
advocates could have supposed; and an imitation of this policy, 
which began in New England, and is rapidly making its way 
southwards, already begins to shed its genial influence over the 
whole of the United States, and must, before any great lapse of 
time, make this country independent of all others for its internal 
resources and supplies. 

Such a state of things in England gave birth to a new profes- 
sion. Artificers and artists were wanting who possessed sufficient 
skill and science to carry these improvements into execution, and 
who could combine with them all the advances of modern re- 
search; and hence arose the Civil Engineer, to whom alone was 
confided the trust of carrying all these valuable improvements 
into effect. If the zeal and energy of England in 1760 could 
produce such changes, what may we not expect from America? 
Her magnitude, and the distance between her principal towns, 
demands a cheap and speedy communication between them for 
the conveyance of merchandise and travellers; and this has already 
been effected by her steamboats and rail-roads to a distance and 
with a rapidity far exceeding any thing that has been done in the 
mother country. Improvements are daily making in her arts 
and manufactures, and thus is the profession of the Engineer 
called into action, and must become more and more in demand 



INTRODUCTION. 21 

as the riches and resources of the country become developed; for 
who will entrust the execution of his improvements or the ex- 
penditure of his money to the ignorant country carpenter or 
blacksmith, when he finds that a set of intelligent and well in- 
structed Engineers are distributed throughout the country? men 
who, from their attainments, will be able to judge correctly of 
the value of all suggestions, and who, from their respectable 
standing in life, will refuse to expend money and time upon them, 
should they be found futile and useless, or who will feel proud 
to execute them and to give them their best attentions and exer- 
tions, should they be found worthy of such fostering care. 

The profession of the Civil Engineer has, like all other pursuits, 
flourished with the progression of society and intelligence. When 
first established in England, Civil Engineers were a self-created 
set of men, whose profession owed its origin, not to power or to 
influence, but to the best of all protection — the necessity for its 
existence, and the encouragement of a great and powerful nation 
that needed their assistance. Still few could follow it, because 
few possessed the means of making the necessary acquirements 
for its successful prosecution. No schools existed for teaching 
them; no books were printed upon the subject, but such as were 
in foreign languages, and therefore inaccessible to many, and so 
large and voluminous as to put them out of the reach of the ma- 
jority of those who could read and make use of them. The im- 
portance of this profession is now^ so fully ascertained, that the 
teaching it on scientific principles has been introduced into several 
of the most respectable colleges of the United States, and it is made 
one of the regular branches of study. Still, however, a difiiculty 
exists in the mode of instruction, from a want of the knowledge 
of what is necessary to be insisted on, and from a want of text 
books; for there is perhaps no mechanic art in which so little 
has appeared in print in the English language as on the subject 
of engineering; and the author believes that the present is the 
first attempt that has ever been made to lay a short and succinct, 
but connected account, of all the objects of the Engineer's profes- 
sion before the public. He is aware that the work is much too 
short to do justice to the subjects, or to be generally useful to the 
practical man. Still he trusts it will be found replete with infor- 
mation on subjects which every one connected with the building 
art ought to possess; and should it meet such favour from the 
public as to call for a second edition in his lifetime, he pledges 
himself to correct the errors that must inevitably creep into a 
first attempt, and to make such amendments, alterations and ad- 
ditions, as may render it more useful and worthy of favour. 



22 



CHAPTER II. 



PHELIMINARY OPERATIONS OF THE ENGINEER, AND AN ACCOUNT OF THE IN- 
STRUMENTS AND IMPLEMENTS NECESSARY FOR THEIR PERFORMANCE. 

Section I. — Of the PriTnary *Mrrangement of Plans, 

1. It is the business of the Civil Engineer to arrange plans for 
the performance and execution of the works he may have to 
carry into efFect, and the object of this treatise is to put him into 
possession of the best means of accomplishing this end, as far as 
the extent of the instructions here given can extend. No one, 
however, must expect to be able to form and digest good plans 
by reading or study alone. Experience and practice are neces- 
sary to produce facility and perfection in this most essential part 
of the profession; and time, patience, and experience must be 
relied upon as the only means of attaining it. 

2. The formation of a first plan for the execution of any work, 
whether it be a road, canal, mill, bridge, or any other construc- 
tion, is an operation of the mind alone; and the first steps towards 
its commencement is as perfect an acquaintance as can be obtained 
of the locality v/here the work is to be executed. This must be 
obtained by visiting and examining the place, and by making the 
necessary inquiries of those who, from living in the vicinity, may 
be supposed to be most able to give the necessary information, 
which will vary with the nature of the proposed construction. 
Thus, for example, if a mill or a bridge has to be built, the par- 
ticulars of the stream upon which it is to be erected, such as its 
width, depth in difierent places, and the velocity with which the 
water flows in a given time, must be ascertained by the Engineer 
himself. He must likewise make himself acquainted with the 
nature of the soil, not only at the bottom, but the two sides of 
the river. This frequently requires that pits should be dug, so 
as to ascertain what exists below the vegetable mould; for upon 
this circumstance will depend the nature of the foundation he 
will have to adopt, whether it must be deep or shallow, wide or 
narrow, or whether it will require the assistance of driving piles. 



PRIMARY ARRANGEMENT OF PLANS. 23 

If one place on the river should thus turn out bad and ineligible, 
he will have to examine others, until he finds one that is more 
efficient; unless, indeed, as is frequently the case from pre-exist- 
ing roads or the limits of private property, he is confined to one 
spot, and then, however bad it may be, it becomes his business 
and duty to make it good and secure by the exercise of his skill 
and contrivance. These and other points he can satisfy himself 
upon by personal examination ; but there are others, almost equally 
essential to the perfection of his plan, and upon which he can 
only obtain information by inquiry — such as the healthiness of 
the place, whether it is subject to drought in dry seasons, or to 
inundations from freshets or floods at other times; and if the lat- 
ter, to what height the water rises, in order that he may elevate 
his constructions above it; the facility that exists of obtaining 
stone, bricks, lime, sand, clay, iron work, timber, and other ma- 
terials, as well as workmen to convert and use them; the price of 
such materials and of wages, and many other points which will 
affect the expedition and expense of the work to be constructed. 
If, on the other hand, it is a road or a canal he is about to con- 
struct, it will be necessary, not only that he should make most 
of the above examinations and enquiries, but, likewise, that he 
should walk or ride over the ground several times, deviating to 
the right and the left, for the purpose of selecting that which, to 
the eye, appears to be the best line, before the labour and ex- 
pense of an actual survey is commenced. If several routes are 
found that seem to offer equal advantages, it may be desirable to 
survey more than one; and then that which is the shortest and 
most level will, of course, be preferred for general purposes. 
In making this cursory examination, strict attention must be paid 
to the position and number of water courses passed over, as well 
as of ravines or bottoms of valleys which, though dry at the time, 
may be expected to contain runs of water in wet seasons. If a 
road is contemplated, all these will require either bridges to be 
built, if they are considerable, or drains under the road to carry 
ofT the water, or shallow fords to be left on its surface; and as 
these, with the exception of the latter, increase the expense very 
considerably, if one route should be found more free from them 
than another, even though it be not quite so direct, it would, in 
general, be preferred. If a canal has to be constructed, such 
^vater courses require even closer inspection and notice. They 
may become highly useful as feeders to supply water to the canal, 
or may be important for carrying away surplus water. In some 
places, on the contrary, they may prove highly detrimental, by 
increasing the height and expense of embankments, or compelling 
the construction of aqueducts for carrying the canal over them. 



24 PRIMARY ARRANGEMENT OP PLANS. 

In these examinations, the information to be obtained from local 
residents is always important. They frequently save much time 
and labour of investigation, by pointing out near cuts or lines 
that, by passing through woods, or being concealed between hills, 
might pass unnoticed by a strange examiner; or would, perhaps, 
not be discovered until much time might have been spent in 
maturing a less eligible route. The Engineer, in making these 
examinations, should never be without his memorandum book, 
and should note down every thing as it occurs upon the spot, and 
not trust to memory, or making remarks at a future period, as 
the number of nearly similar objects that engage his attention in 
succession is, in that case, very apt to produce confusion and 
mistakes. If he is going over the investigation of a line for the 
first time, he will save much future trouble by ascertaining and 
putting down the names of the proprietors of the land he passes 
through, as well as the nature and quality of that land, and its de- 
gree of cultivation. And if he is proceeding over a line for the 
purpose of marking out and locating the work upon the ground, 
for any public undertaking, he ought to be provided with the 
agreement or act of legislature, by which it is authorized, in or- 
der that he may know the precise extent of his own, or his em- 
ployers' power, and the exact line he has to run, and may thus 
guard against trespassing upon any land, which had been previous- 
ly protected, or was not intended to be infringed upon. 

3. Winter, and even sharp frosty weather, is generally con- 
sidered as the best season of the year for making these first in- 
vestigations, provided the ground is not obscured by being thickly 
covered with snow. The reason of this is, that in woody coun- 
tries the leaves are off*, and it is possible to see farther, and to 
measure with greater facility, than in the full foliage of summer.^ 
Small rivers, water courses, morasses, and other wet places, which 
might offer impediments to pursuing a straight course, if frozen, 
will be passable without difficulty; and all crops of corn and other 
produce are off* the ground, and therefore not subject to injury. 
In addition to this, the general building operations of the Engineer 
are necessarily suspended at this season of the year, and he there- 
fore has more time to devote to these primary investigations. It 
is, moreover, more healthy and pleasant to the Engineer to be 
moving about in the active exercise that these examinations re- 
quire, than to be compelled to perform such duty in the sultry 
days of summer. In general, therefore, the Engineer stakes or 
lays out roads, canals, and other extended constructions, in the 
early spring of the year, in order that the w^orkmen may com- 
mence operations upon them as soon as the frost will permit the 
ground to be moved; and the employer has then the advantage of 



PRIMARY ARRANGEMENT OF PLANS. 25 

having his work executed in the lengthening days of spring and 
longer ones of summer. 

4. The Engineer having thus made himself fully acquainted 
with the ground he has to work upon, and the nature of the ma- 
terials with which he can be supplied, has next to form and digest 
his plans. This will require the utmost exertion of his mental 
faculties, in order that he may turn everything he is in possession 
of to the greatest advantage for the perfection of what he has to 
produce. He will here find ample scope for the exercise of his 
inventive faculties and genius; but while young in his profession, 
should not be too vainly confident in his own resources, but must 
be satisfied with imitating, or rather correctly copying, what 
others of more experience have done before him. 

5. The young Engineer should never be without his memo- 
randum book and pen or pencil. Whenever he meets with a 
machine or piece of construction that has obtained a good charac- 
ter for performing well, he ought (even if he does not take a 
sketch of the whole of it) to note down the form and disposition 
of the several parts, the materials it is composed of, tlieir dimen- 
sions, mode of connexion and operation upon each other; the 
power employed, the mode of olftaining it, the result which it 
produces, and the expenditure of time and money necessary to 
that result, whether it be in wages, fuel, or wear and tear. If 
parts of the machine are nidden from the eye, he will in general 
be able to obtain such information from the workmen about it as 
will enable him to describe it; and this should in all cases be done, 
unless indeed it is a contrivance that the proprietor has purposely 
concealed for his own advantage, as being his own property; and 
in that case common delicacy a-tid courtesy would prevent any 
one from making enquiry about it. Even if a machine is pal- 
pably bad, and has been discarded from its insufficiency, it will 
be well in many cases to note down its particulars; because, while 
the first will furnish much valuable information to copy from, the 
latter (which would never have been constructed, had not hopes 
been entertained of its being good and effective) will in many 
cases prevent the young and inexperienced Engineer from falling 
into similar errors. By persevering in this practice of taking 
memoranda of whatever comes under the notice of the young 
Engineer, and keeping them carefully in books, the subjects of 
which can be afterwards arranged and indexed, he will find that 
in a few years he will be in possession of a stock of practical 
knowledge that will be invaluable to him in after life. In making 
out his future plans, whenever his own invention or resources 
fail him, he may go to these memoranda, which will frequently 
help him out. Or he may adopt the more laudable plan of ar- 

4 



^6 PRIMARY ARRANGEMENT OF PLANS. 

ranging his own views as to the means of carrying an object into 
effect, and may then compare his own plan when mature, with 
the information he has so gleaned; and this will in all probability 
convince him that his own ideas are good and worthy to be acted 
upon, or may show him what alterations he ought to make to 
render his plan more perfect, 

6. Having arranged the plan of what he proposes to do in his 
own mind, he must in the next place render it palpable to others, 
so that its merits and defects may be canvassed and investigated, 
and the whole be rendered plain and intelligible to the public, or 
at all events to his employer, and to the workmen who are to 
have charge of the execution and fulfilment of the design; and 
this is generally done in two ways: 1st. By such drawings as 
will show the arrangement, form, proportion and disposition of 
the parts to each other; and 2ndly. By a written description re- 
ferring to such drawings, and which is called the specification, or 
particulars of the work to be executed. If a drawing is made, 
and even coloured with the greatest care and accuracy, it will be 
impossible by its means alone, to convey all the information ne- 
cessary to the workman, and hence all these unavoidable defi- 
ciencies must be made up by the specification. A drawing, for 
example, may show what parts of a construction are to be made 
of timber, what of iron, and what of brickwork, but it cannot 
show whether that timber is to be pine, oak, poplar, or of other 
wood. Cast iron and wrought iron could not be clearly distin- 
guished from each other in a drawing; and although brickwork 
might be shown, yet the particular bond or mode of laying the 
bricks could not be designated without endless trouble. All this, 
therefore, is left to be described in the specification. So also of 
windows, roofing, and many other things. Should any one take 
the trouble of putting each square of glass in a window, or marking 
the exact size of the shingles or slates with which a building is 
covered, into a drawing, the labour would be thrown away; for 
they might be too minute to be measured accurately, or the work- 
man might not choose to take the trouble of counting them. 
Such things are on this account much better left out of the draw- 
ing, which makes it more simple and intelligible, and are intro- 
duced into the specification by saying that each window is to have 
a common sash with twelve panes of glass, of 10 by 12 inches, 
or as the case may require; and that the roof of the building is 
to be covered with slates of a certain size, or with good Cyprus 
shingles, seventy-two to the square yard, each shingle being fixed 
with two nails, &c., when of course nothing ambiguous or uncer- 
tain remains. 



OF DRAWING. 2*7 

In the next place we will consider the kind of drawing made 
use of by the Engineer. 

Section II. — Of Drawings and Drawing Instruments. 

7. It is quite essential to the profession of an Engineer that 
he should be a tolerable good draughtsman; because, in general, 
better and more perfect ideas of the arrangement and disposition 
of a construction are given by a drawing than in any other way, 
except, indeed; by a model, which is sometimes necessary for 
complicated things. But as the Engineer is not supposed to be 
a practical workman, and such a one must be employed to con- 
struct the model, so a drawing is necessary in the first instance 
for the guidance of such workman. In some few instances a 
piece of work may be so simple as to admit of a clear description 
in words, and in that case the specification is all that is necessary. 
But it more frequently happens that a drawing alone is necessary, 
and that the specification may be dispensed with, although they 
generally accompany each other. 

8. A correct drawing of what has to be constructed may, 
therefore, be considered as indispensable in all the operations of 
the Engineer; and if he is unable to make his own drawings, he 
will have to employ others to supply the deficiency at great ex- 
pense; for a good draughtsman always receives higher pay than 
those employed in other junior departments of the profession. 
This should act as an inducement to students to apply steadily to 
this art, which requires nothing more than care, attention, and 
assiduity for its acquirement. Moreover, the Engineer will find 
that few second persons can convey his ideas, and put them down 
on paper, in such direct accordance with his own views and 
wishes, as he can do himself. And on this account it is strongly 
recommended to all students, in this profession, to devote as much 
time as they can spare to this desirable accomplishment. 

9. The drawing requisite for an Engineer to pursue, is of a 
character quite different from that pursued by artists, or those 
w^ho follow the profession of producing pictures as works of art, 
or for ornamental purposes. This branch of art requires great 
skill and practice; a correct eye, and judgment to depict forms 
and their proportions as they appear, without measuring them; 
for, in this kind of drawing, the rule and compasses are never 
used; a knowledge of the rules of perspective; a correct dis- 
crimination of colours, so as to imitate upon paper or canvass, 
what is seen in nature; a freedom of touch, and facility of soften- 
ing down and diminishing the distinctness of objects, to produce 
the effect of distance; a complete acquaintance with the effects of 



2S or DRAWING. 

light and shadow, and a knowledge of the picturesque, or that 
form and disposition of things which, by rules of art, is said to 
constitute beauty. An artist must also be able to depict correct- 
ly the appearance of the sky and clouds which, from their 
irregularity and indistinctness, is very difficult, and can only be 
acquired by the study and observation of nature, and making 
constant efforts to imitate that which is seen. It frequently be- 
comes necessary to introduce trees, or other objects, in the fore- 
ground, that do not exist in the real view; a license that is per- 
mitted him, because, without such assistance, he might not be 
able to give the proper effect to the other parts of his picture. It 
is the combination of all these things, and a want of knowledge 
when and how to use them, that makes picturesque drawing so 
difficult of acquirement. If an Engineer possesses this knowledge 
and the above qualifications, his drawings will be more pleasing 
to the eye, but they will not be more useful to the mechanic or 
the workman; for none of the requisites of a picture are necessa- 
ry in the drawing of an Engineer; but, inasmuch as they add to 
its beauty, it is by no means uncommon for the Engineer to 
make his own drawing of that which appertains to his profession, 
and afterwards to employ an artist to finish and decorate it. Thus, 
for example, if he has made a design for a bridge, all he has to do 
is to show the form of the arches, their number and proportion, 
the manner in which the stones are to be cut, laid, and joined to 
each other; but he has nothing to do with giving a view or re- 
presentation of the river that passes under that bridge, the boats 
that sail or move upon it, and the houses, woods, hills, or other 
objects that may be upon the two shores; and all these he can 
get introduced upon his paper by a professional artist after his 
drawing is completed, if it should be desirable to do so. But 
it will be self-evident that the drawing will be equally valid and 
useful to the workmen, who have to build that bridge, without 
such embellishments. Still, however, cases do sometimes occur 
where it is desirable, from motives of policy, to finish drawings 
in this style. 

10. The regular dravv^ing of the Engineer, in fact, requires 
none of the conditions just enumerated, and for the most part 
consists of straight lines and curves, for the production of which 
there are appropriate instruments, so that it is purely mechanical. 
Every object requires to be made out clearly and distinctly, with- 
out regard to distance. Perspective is rarely admitted into it, 
because perspective is the art of representing objects by geome- 
trical rules, upon a plane or flat surface, in the way in which they 
appear to the eye; and, consequently, all objects must be drawn 
smaller, if they are distant, notwithstanding that their dimensions 



OF DRAWING. 29 

are similar, and would appear so if viewed from equal distances. 
If a circle is viewed obliquely to its plane, it must be represent- 
ed in perspective by an oval, therefore the represented form does 
not agree with the real form. Now, in the drawings of the En- 
gineer, every object must have its real form and proportion, in- 
stead of its apparent ones; a circle must always be a circle, and 
all things that have the same length or height must have those 
heights assigned to them, because the workman has to apply his 
rule or compasses to the drawing, and must be able to obtain the 
magnitude of the real thing to be executed from the small repre- 
sentation of it. tience it will appear that perspective is inadmis- 
sible in the principal drawings of the Engineer, though he fre- 
quently makes use of it in an accessory or auxiliary drawing, 
which is not to be measured from, but is merely to show the 
general form and disposition of the parts figured upon his other 
drawings. The kind of drawing necessary to the Engineer is, 
therefore, so simple, and easy of acquirement, that any person 
with a steady hand, and possessing the necessary instruments and 
materials, may make himself master of it without an instructor, 
and that even to a considerable degree of excellence, by nothing 
more than the exercise of great care and attention, industry and 
perseverance in practice, and his own determination to excel. 
The best practice for the beginner, is to acquire the habit of draw- 
ing perfectly straight lines of even thickness throughout, by a 
pencil, or pen and ink and ruler, and also to produce circles of 
different diameters with a pair of compasses. Then to endeavour 
to do the same things by hand, unassisted by the ruler or com- 
passes; also to lay down different angles; to draw the several 
solid geometrical figures in perspective, giving them the necessa- 
ry shadows, and then to copy outline figures of machines, houses, 
the columns of architecture, and other simple figures which are 
to be found in many books, and then to attempt the same things 
filled in, and shaded. After this it Vv'ill be well to attempt draw- 
ing from models or instruments themselves, instead of from re- 
presentations of them. 

11. The drawings proper, which every Engineer has to exe- 
cute, are constantly three in number of the same thing. These 
are — 1st. The ground plan or horizontal appearance of a thing 
as seen from above; and which, if the object is a country, or 
estate, or road, or canal, is called the map ox plan, 

2nd. The longitudinal elevation^ which is the external ap- 
pearance that a thing will put on when finished and viewed with 
its longest dimension turned towards the eye. 

3d. The transverse elevation, or external appearance of the 



30 OF DRAWING. 

end or side, which is at right angles, or otherwise connected with 
the last. All these go by the general name of plans. 

The above is on the presumption that the back and front of 
the construction, and its two ends, are similar; as in the case of 
bridges, steam-engines, &c. But if a construction has more than 
two sides that are dissimilar, then it will be necessary to have a 
separate elevation for each of them. 

12. When an elevation consists of a repetition of the same 
parts, such as columns, windows, and the like, with similar spaces 
between them, the drawing of one such object and its space on 
either side, with a notification of the number of times they are to 
be repeated, will often suffice, and save the time and labour of 
a drawing containing all the details; and, in the case of bridges, 
either of a single arch, or any number of arches, the elevation 
very frequently exhibits but half the bridge, taken from its abut- 
ment upon one shore to the middle of the arch, or centre arch, 
as the case may be. And as both ends of a bridge are almost con- 
stantly alike, it will be evident that such a drawing will convey 
all the information that is necessary to the v/orkman for the con- 
struction, and will save half the time, labour, and expense of an 
entire drawing, which, after all, could contain nothing more than 
a repetition of that which appeared in the first half. 

13. All these several drawings must be perfect representations 
in every respect of that which has been, or that which is proposed 
to be, constructed. They must not be mere pictures, giving an 
idea of the general form and appearance of the thing, but must 
exhibit every detail with minute accuracy. On this account 
mouldings, ornaments, modes of fixing together, and man)^ other 
minutiae, are drawn upon a much larger scale than the general 
plans, and are put upon separate sheets, and referred to in the 
general plan. Every object that is introduced into these several 
drawings requires to be laid down with the most scrupulous at- 
tention to magnitude and relative proportion; because it is by 
measuring these drawings that the workman determines the size 
of the things, or parts of things, to be constructed; and on this 
account it is very desirable that the same scale of magnitude 
should be adopted in all the general plans and elevations that are 
made for the same construction, and the scale to which they are 
drawn should be introduced, or mentioned, on some convenient 
part of the paper. 

14. The expression drawing to scale may require some ex- 
planation, but is very simple. It is merely supposmg a small 
quantity of space to be the representative of a larger one, or vice 
versa, and is generally determined by the magnitude of the paper 
made use of. Thus the Engineer who is about to make a design 



OF DRAWING. 31 

for a bridge, may say that each foot of his real bridge, when built, 
shall occupy one inch upon the paper of his drawing. Then the 
inch becomes the representative of a foot, and the drawing would 
be said to be upon an inch scale. If the bridge is to be thirty 
feet long in reality, then the length of the drawing must be thirty 
inches, and each inch being divided into twelve equal parts, each 
of those parts will become the representative of an inch in reality. 
On attempting to make his drawing he finds that his sheet of 
drawing-paper is but two feet five inches long, and consequently 
will not hold the bridge, unless two sheets are joined together, 
which always disfigures a drawing, unless very neatly done. This 
must be submitted to, or the scale must be reduced. Half an inch 
may, therefore, be made to represent a foot; but with a half inch 
scale the bridge will only be fifteen inches long, and that will 
look too small for the paper; but by adopting a three quarter 
inch scale, the length will be twenty -two and a half inches, and 
this will fill the paper very well and leave a handsome margin. 
In this way then the scale may be predetermined, and the paper 
made commensurate with it, or it may be adapted to the size of 
the paper, as may be most desirable. For the details of work, 
as above referred to, a scale of two, or sometimes three inches to 
the foot is often adopted, while the three inches is often made to 
represent a mile in a plan of a road; and six inches, or a foot, to a 
mile, is a good scale for plans of canals. An inch or half an inch 
to the foot scale, is very frequently used for mill-work and ma- 
chinery; and maps of countries are often drawn at four miles or 
more to the inch; but in these cases there is not room for the ac- 
curacy required in the operations of the Engineer. 

15. In addition to the plan and elevations above referred to, 
the Engineer has frequent occasion to produce another drawing, 
or set of drawings, which are sectional, or represent sections of 
the thing indicated, or the exact appearance the object would as- 
sume if it were sawed through, or cut in the direction of certain 
lines, which must always be represented or referred to in the or- 
dinary plan and elevation. These lines represent a plane or flat 
surface, that is imagined to pass through the object represented. 
Sectional drawings are highly useful and important, and rank in 
a higher order than mere plans and elevations; because any one 
of ordinary skill can produce a plan and elevation of an object 
that stands before him, or can copy a sectional drawing; but it is 
not every one that can produce an original section; for this 
requires thought, experience, a knowledge of workmanship, 
or the means of uniting things together, of strength of ma- 
terials, and of mathematical principles which cannot be ex- 
pected in the unexperienced. The production of a sectional 



32 OF DRAWING. 

drawing even of an object that stands before us, and consequently 
has not to be contrived and designed, is attended with some dif- 
ficulty; because a section always represents that which can never 
be seen by the eye, and consequently can only be imagined. 
We can never cut a steam engine or any other machine in half 
for the purpose of ascertaining how it would appear; but if we 
have a perfect knowledge of the shape, use, operation, and mode 
of putting every part together, we shall have no difficulty in con- 
ceiving in the mind how it would appear if so cutj and of drawing 
the appearance that all the parts would assume on paper. Nothing, 
perhaps, offers clearer evidence of the practical ability of an En- 
gineer, than his being able to produce a good and perfect original 
sectional drawing. Because, to do this, as he has nothing to copy 
from, and must express and lay down all the parts in good and 
effective proportions — must select his materials, and show the 
mode of uniting and putting them together — the whole must 
spring from his mind and inventive genius, coupled with his 
knowledge of the strength and efficacy of the several parts to 
withstand the resistance opposed to them, and to effectually an- 
swer the several purposes for which they are intended and intro- 
4uced; and no man can do this without practice, experience, and 
a considerable knowledge of the object he has in view. 

16. Sectional drawings are used by Engineers and Architects 
to instruct workmen in the interior and particular construction 
of machines or other constructions, such as the framing and putting 
together of roofs, partitions, and the internal parts of bridges; 
and are so generally useful that they should be much studied and 
practised by all who wish to excel in their profession. 

17. To execute drawings, certain materials and apparatus are 
necessary, and these will be the next object of description. 

The paper upon which the drawing is to be made is the first 
requisite. For sketches, first thoughts, and rough memoranda, 
any ordinary writing paper will suffice; but as the finished plans 
of the Engineer and Architect frequently require to be much 
larger than this kind of paper is made, a thick and fine paper is 
manufactured for the express purpose of drawing upon, and is 
called drawing paper. This kind of paper has various names 
given to it by the manufacturer, all of which depend upon the 
size of the sheets; and as this volume may fall into the hands of 
persons in the country who may have occasion to send to the 
cities for such paper, a list of the names and sizes of the sheets 
is annexed, in order that persons may know what to ask for to 
suit their several purposes. 



Royal 




do. 


Super- 


•royal 


do. 


Imperial 


do. 


Eleph! 


ant 


do. 


Colum 


bier 


do. 


Atlas 




do. 


Double 


3 elephar 


it do. 


Wove 


antique 


do. 



\et. 


Inches. Feet. 


Inches. 


1 


5 by 1 


1 


1 


10 by 1 


6 


2 


by 1 


7 


2 


3 by 1 


7 


2 


5 by 1 




2 


4 by 1 


101 


2 


10 by 1 


11 


2 


9 by 2 


2 


3 


4 by 2 


2 


4 


4 by 2 


7 



OF DRAWING INSTRTTMENTS AND IMPLEMENTS. 33 

18. Size and denomination of Drawing Paper. 

Thick woven drawing foolscap, each sheet, 

Medium drawing paper, - ,, - 

~ ~ ?> ~ 

~ ~ ?> " 

~ " 3? ~ 

~ " >? " 

~ ~ ?? " 

"*■??" 

" " 3? ■" 

" ~ J5 " 

Anything larger than the above can only be obtained by past- 
ing or otherwise joining two or more sheets together.'^ 

19. The larger kinds of drawing paper are very expensive; 
and as a good drawing occupies much time and is otherwise 
valuable, every Engineer should provide himself with a tin case, 
or cases, of sufficient length to contain the sheet when rolled, for 
the purpose of carrying his drawings about and preserving them; 
but at home no drawing should be rolled or folded up, as the best 
of paper will soon give way in the crease, by frequent opening 
and shutting. A good collection of working drawings may be 
said to be the stock in trade of the Engineer and Architect, and 
they will prove of immense use to him in the pursuit of his pro- 
fession. Every young Engineer ought therefore to strive to 
make such a collection by his own or other hands, and to preserve 
them carefully when obtained. A small quantity of drawings 
may be kept in a portfolio; but when they accumulate, it will be 
found most convenient to arrange them according to subjects, and 
to lay them flat in drawers. 

20. When large paper is made use of, and indeed in all cases, 
a drawing-board is essential; that is, a perfectly smooth board, 
rather larger than the paper used, to strain it upon and keep it 

* Flour paste is much superior to gum, glue, or any other composition, for 
joining sheets of paper together. To make it, use the best wheat flour, and 
add, by degrees, as much cold rain or soft water as will mix with it to the con- 
sistence of thick cream. Stir or beat it well while cold, so as to leave no lumps 
of flour unbroken. To insure that this has been done effectually, the mixture 
may be strained through a cullender. Then place the vessel containing it over 
a slow fire, and heat it gradually till it boils, stirring it the whole time with a 
stick or wooden spatula. Do not continue the boiling, but as soon as it turns 
yellow move it from the fire; stir it occasionally as it cools, and use it when 
cold. A little powdered alum dissolved in the water is said to prevent its be- 
coming mouldy by keeping; and corrosive sublimate, dissolved in the water of 
which it is made, being poisonous, prevents its being attacked by the cockroach 
and weevle in hot countries. 
5 



34 OF DRAWING INSTRUMENTS AND IMPLEMENTS. 

perfectly flat and free from creases. The drawing board must 
have its surface not only quite flat and smooth, but should be free 
from all holes, knots, and hard grain, and be as nearly of the 
same hardness in every part as possible, otherwise the points of 
the compasses will scarcely mark in some places, and in others 
will sink in, making large holes in the paper and disfiguring the 
drawing. White pine makes a very good board, but Bay or 
Honduras mahogany is the best, as being more homogeneous. 
It must be clamped* at the two ends to prevent its warping. 

21. The sheet of paper is fixed upon the drawing-board by 
applying a little paste to the four corners, or to the sides of the 
paper, if large; taking care that the paste does not extend more 
than a quarter of an inch under the paper, as that would prevent 
the cutting of the drawing off the board when finished. In the 
absence of paste the paper may be laid down with a few wafers, 
or touches of sealing wax, which must be scraped or washed off 
the board after the drawing is removed. 

22. If it is intended to tint or colour the drawing, then the 
drawing paper must be made damp by wetting the back of the 
sheet with a sponge, or rag, and clean water, before applying it 
to the drawing-board, upon which it must be stretched, with the 
damp side downwards, before it gets quite dry. It must then be 
set by, to dry slowly, and must become quite dry before any 
drawing is made upon it. The reason of this is, that all paper 
expands considerably in its dimensions by being wetted. If, 
therefore, we attempt to lay water-colour tints to any extent upon 
dry paper, the part so coloured will cockle up, and acquire so 
uneven a surface, that it will be impossible to dispose the colour 
evenly upon it; and it will even dry with these inequalities, 
which cannot afterwards be removed except by the damping 
process, which may injure the drawing. But when a sheet of 
paper is so wetted and expanded in the first instance before it is 
put upon the drawing-board, it is prevented from shrinking to 
the full extent, but will dry perfectly smooth, and may be worked 
upon in a very satisfactory manner. 

23. The best drawing boards are made so as to confine a sheet 
of paper, either dry or damp, without paste or any adhesive ma- 
terial. These consist of a frame of mahogany or other hard wood, 
strongly mortised* together, about two inches wide and full an 
inch thick. The opening in the middle of the frame must be an 
inch and a half each way less in size than the sheet of paper in- 
tended to be used. The drawing-board is only half an inch thick, 
and fits the opening of the frame, being rebated* into the same 

* For explanation of these and other unexplained terms, look for them by the 
Index. » • 



OF DRAWING INSTRUMENTS AND IMPLEMENTS. 35 

on all the four sides. The paper being placed on this board so 
as to extend an equal distance beyond it on every side, the frame 
is to be pressed down on to the same, when the edges of the paper 
will fold into the rebates, and the central pannel of the drawing- 
board is held in its place in the frame by turnbuckles or other 
contrivances fixed upon the back of it, and which thus hold the 
paper quite securely. Whatever be the construction of a drawing- 
board, it is quite essential that its sides should be quite flat and 
straight, and those opposite to each other parallel, and that the 
corners should be right angles. 

24. The paper being so fixed and prepared, the drawing may 
be commenced with a black-lead pencil, which must in every 
case be used for beginning a drawing, on account of the facility 
with which its lines may be ejflfaced, if wrong, by a piece of 
caoutchouc, gum elastic or India rubber. If that is not at hand, 
the best substitute for it is a small piece of new wheat or rye 
bread, free from crust or grease. This is to be worked or kneaded 
between the fingers until it becomes perfectly plastic and elastic, 
and will not fall into crumbs. With this any traces or lines made 
with a black-lead pencil or black chalk may be very efiectually 
removed. 

25. There is a great difference in the goodness of black-lead 
pencils, and those that are warranted are always high priced. 
The make of Brookman and Langdon of London are most ap- 
proved, and they cost sixteen cents each at the manufactory. 
They assort their lead according to hardness and colour, and 
stamp their pencils with the letters HH for hardest hard, H for 
hard, M middling, S soft, SS softest soft, B black, and BB very 
black. A soft pencil should always be used to lay down the first 
points or parts of a drawing, because its marks are easily rubbed 
out. A hard or harder pencil is used after to put in the more 
finished and detailed parts; but the whole of these need not be 
inserted in pencil, because when the outline is set out and nearly 
finished, so as to ascertain if it is perfect and will answer its in- 
tended purpose, the whole must be gone over again and be inked 
in; and in this process all the minute parts that have not been 
attended to with the pencil may be finished with the ink. 

26. Comition writing ink must in no case be used for finishing 
drawings, because that dissolves and spoils the appearance of 
every line that is tinted or coloured over. China or Indian ink, 
such as is imported in cakes or sticks from China, is the only ink 
that is admissible. To use this, small blocks of white earthen- 
ware, with several concave recesses, and a long channel, deeper 
at one end than the other, and which are called ink stones, are 
very convenient. The end of the stick of ink is rubbed back- 



36 OP DRAWING INSTRUMENTS AND IMPLEMENTS. 

wards and forwards in a little clean water, 'until a sufficient quan- 
tity of the ink is dissolved to make the fluid as black as required, 
which must be ascertained by trial. The long channel being deep 
at one end, the dissolved ink will lie in that part, and a sufficient 
quantity ©f ink should be rubbed down to last for hours, or even 
days, because it will keep well if protected from dust. The 
concave circular cavities are for holding clean water, or mixing 
a quantity of black tint for shading drawings. Of this a quantity 
should be prepared at once, to insure uniformity of tint or dark- 
ness. A camePs hair pencil is kept in the long channel of the 
ink stone, and with this the ink is taken up to charge a common 
quill pen, or one of the steel ruling pens to be hereafter described, 
because the pen of either kind should never be dipped in the ink, 
which would injure its point. 

27. China ink, if good, should be entirely free from grit or 
dirt, and should make an even, well defined line, when drawn 
upon paper. That line, when dry, should bear tinting or colour- 
ing over without washing up or mixing with the colour applied 
above it. In the event of making a mistake, and placing lines, 
blots, or marks upon your drawing that should not be there, 
never use a knife for scratching out or erasing them; but if they 
have been made with China ink or good water colours, wet the 
whole of them thoroughly with clean water, applied with a large 
and clean camePs hair brush, and let the water remain on until 
the paper is rendered rather soft and you think the colour is dis- 
solved, which will seldom occupy above a minute; then apply 
blotting paper perpendicularly, or without lateral motion, and by 
pressure with the hand and renewed applications, get all the hu- 
midity absorbed and taken up; which done, apply India rubber 
(as to a pencil line) before the paper becomes dry; but instead of 
rubbing backwards and forwards, rub in one direction only, and 
the line or marks will be taken out as effectually as if they had 
never existed, and the surface of the paper will be left so perfect 
that it may be coloured or written upon, and no trace of the 
erasure will be visible, except by transmitted light on account of 
the paper having become thinner. 

28. The next implements to be mentioned are rulers for draw- 
ing right or straight lines, and of these the draughtsman should 
possess at least three — one a few inches long, as from four to six 
inches, for short lines; the next two feet three inches long, and 
a third about three feet six inches. These should be formed out 
of strips of hard wood, from one to three inches wide, according 
to their length, and need in no case exceed a quarter of an inch 
in thickness. They should be quite flat, so as/to come into per- 
fect contact with the paper. Their two edges should be parallel. 



OF DRAWING INSTRUMENTS AND IMPLEMENTS. 3/ 

one being made square "or at right angles to its sides and to the 
paper upon which it is placed, and the other edge should be 
chamferred, or formed with a sharp or fiducial edge. This edge 
is to be used with its chamfer towards the paper, and this edge 
uppermost for drawing ink lines, and in the reversed position for 
drawing very fine pencil lines. In drawing a long right line, 
the ruler ought not to be shifted or moved, after once laid down 
and adjusted to its place, until the line is drawn; and it is on this 
account that the above lengths of rulers are assigned, for two feet 
three inches will extend quite across the longest dimensions of the 
first four kinds of drawing-paper, mentioned in the list at page 
33, and these are the papers most commonly used, while three 
feet six inches will compass all the varieties of paper, except the 
last, and that is seldom met with. 

29. To try the goodness of a ruler, draw as even and perfect 
a line as possible with it upon a well strained sheet of paper, 
and then reverse the paper, by placing the side that is most dis- 
tant from you, next to you, and draw another line close to the 
first with the same edge of the ruler, and if the two lines coin- 
cide, or are perfectly parallel throughout, the edge is straight and 
perfect; but if the ruler is concave or convex, its error will be 
doubled by this process, and will become apparent to the eye. 

30. All large drawings should be executed on a high table, and 
in a standing position, not only as the most healthy, but it gives 
a greater command over the work, and enables the draughtsman 
to look down close to the edge of the ruler, which cannot be done 
while sitting, except in small work. 

31. Some lead weights, not exceeding three-quarters of an 
inch in thickness, and two or three inches square, covered with 
paper or cloth, to prevent their soiling the paper, will be very 
serviceable to the draughtsman for placing on the sides or cor- 
ners of drawings, that have a tendency to curl, from having been 
previously rolled. In drawing long lines with a ruler, these 
weights must be placed upon the ruler to keep it in its place; it 
being impossible to hold a long ruler steadily to its position with 
one hand, while the other is employed in drawing the line. Some 
persons employ an assistant to steady the ruler, but the weights 
are more certain, and are constantly at hand. 

32. It is very frequently necessary to draw parallel right lines, 
or to make them at right angles, or perpendicular to each other. 
To set out such lines by the rules of geometry occasions a waste 
of time, as mechanical implements are provided for these pur- 
poses. The instruments cabled parallel rulers, consist of two 
slips or rulers, united together by two brass connecting pieces, 
which permit them to be separated, or placed in contact with each 



38 OF DRAWING INSTRUMENTS AND IMPLEMENTS. 

other. Sometimes three rulers and four connectins; links are 
used; and occasionally a single ruler is mounted upon two small 
wheels of exactly the same diameter, and which are connected to- 
gether by a concealed steel wire that prevents the one turning with- 
out the other, or their moving in opposite directions. Such instru- 
ments answer very well when they are small, as not more than 
six inches long; and such an instrument is more convenient than 
the small simple ruler before referred to. But for cheapness, ac- 
curacy, and expedition, the French parallel ruler called Mar- 
quois's, from its inventor, is decidedly the best for the Engineer 
and draughtsman, and no other will be necessary. It consists of 
a thin flat triangular piece of hard wood, one angle of which 
should be a right angle, in order that it may be used for drawing 
perpendiculars, or lines at right angles to each other. To employ 
this triangle as a parallel ruler, it must be used in contact with 
the common flat ruler, and its application will be obvious on in- 
spection o^ Fig. 1, Plate /., in which, let a b represent a right 
line previously drawn upon the paper, and to which it is desira- 
ble to make other lines parallel — place the w^ooden triangle, cde, 
upon the paper in such manner that any one of its three sides 
may be in contact with, or parallel to, the given line a h. The 
hypotenuse of the triangle will, in general, be the most conve- 
nient, because it is the longest side. That done^ hold the trian- 
gle firmly down in its position with one hand, while with the 
other the flat ruler, f g^ is brought into contact with the other 
side, d e^ of the triangle. The ruler, /"o*, has now in its turn to 
be firmly held down, when the triangle may be made to move 
or slide along the ruler, during which movement, the side, c e, 
will always be parallel to a b; consequently, any lines drawn 
against its edge, c e, will be parallel to a b. 

The long side, c e, of the triangle should be chamferred on one 
side to render it fit for drawing ink lines, or by reversing it, to 
make a thin edge for pencil drawing. 

33. In drawing buildings, and the frame-work of machinery, 
a great number of lines are generally required perpendicular to 
a horizontal base line, and consequently parallel to each other; 
and these are most expeditiously and correctly produced by what 
is called a T square, the form of which is shown at Fig. 2, Plate 
I. The blade, h i, is a common thin and flat ruler, which is let 
into and immovably fixed, at right angles, to the stock k, which 
is made of thicker wood, so that while the blade lies in contact 
with a sheet of paper, strained upon a drawing-board, the inner 
edge of the stock may be brought into contact with, and be made 
to slide against either side of the drawing-board, and thus any 
number of lines may be drawn against the edges of h z, all 



OF DRAWING INSTRUMENTS AND IMPLEMENTS. 39 

parallel to each other, and perpendicular to that side of the draw- 
ing-board to which the stock is applied. The stock of this in- 
strument is sometimes made of two parallel and similar pieces of 
wood; one of which is fixed to the blade, and the other attached 
by the screw /, upon which it turns as a pivot, and may be set 
to any required angle, as shown by the dotted lines in the figure; 
and if this dotted half of the stock is applied to the edge of the 
drawing-board, the blade will no longer be perpendicular to it, 
but any number of lines may be drawn, all parallel to each other, 
and with any required angular direction, in respect to the base 
line. 

34. To 2^TQve the correctness of a T, or other square. Bring 
the stock of the T square into close contact with one side of the 
drawing-board, and draw a fine but correct line by one edge of 
the blade; and then turn the square over so that the other side of 
the blade may come into contact with the paper and the edge of 
the blade before used into contact with the line, and then draw 
another line. If the two lines are parallel to each other, or if 
the last line covers or coincides with the first, the square must 
be correct, while, on the contrary, if this is not the case, the lines 
will make a small angle with each other, and the true square will 
be an intermediate line bisecting that angle. If the square to be 
tried is not of the T kind, and has not a thick stock, as in the 
case of the triangular ruler, c d e, in Fig. 1., a line must be 
drawn to serve as a base, and a perpendicular be erected upon 
the middle of it by the square, which is afterwards to be turned 
over on to the other right angle formed by the two lines, and if 
a perfect coincidence between the lines and the right angle of the 
square still holds goods, the square is true. 

35. In addition to the implements for drawing before men- 
tioned, the following instruments are absolutely necessary, 
viz: — 

A steel drawing-pen. 

A pair of compasses with shifting points for ink or pencil. 
A marking-point or pricker. 

A protractor for laying down and measuring angles, and a 
scale, or several scales of equal parts. 

36. The drawing-pen is not intended to be used either for 
writing or drawing curved or irregular figures, but is solely for 
drawing right lines with Indian or other ink against the edge of 
a ruler. This pen consists of two thin plates of hard steel, fixed 
parallel to each other, at the end of a brass handle, in such man- 
ner that their points may spring away from each other to a small 
distance; but they may be brought into close contact, or be set 
to any required distance apart, by a small screw that passes 



40 OF DRAWING INSTRUMENTS AND IMPLEMENTS. 

through them both, and can be turned by its milled head. The 
steel plates are ground upon a hone until they are very thin, and 
they should not terminate in a sharp point, but be made nearly 
semicircular, so as to insure their not scratching the paper, whether 
the pen be held upright or in a sloping position. By means of 
the adjusting screw the thickness of the line to be drawn is re- 
gulated, since it w4ll depend upon the distance the plates or 
cheeks of the pen are from each other. In using these pens they 
should always be held perpendicular to the plane of the paper or 
to a line that joins the top and bottom of the sheet, but sloping 
as to the right or the left. They should never be dipped into 
the ink, but are to be fed or supplied when necessary by a camel's 
hair pencil dipped in dissolved China ink, and the required line 
must be produced by drawing, and not pushing the pen forward 
against the ruler. Those pens are the best in which the cheeks 
are allowed to separate from each other by a hinge, after the ad- 
justing screw is removed; because this admits of the points being 
wiped clean after using; and cleanliness with sharp edges are 
essential to the perfection of their operation, consequently after 
long use the points of a pen of this description will require re- 
setting upon a hone or oil-stone, like a penknife. As this pen 
is to be used for drawing right lines only, so 

37. The compasses with shifting points are for drawing cir- 
cles and curves, as well as for measuring and setting ofi" dis- 
tances. The form of a pair of compasses, or dividers, as they are 
sometimes called, is too well known to need description. As 
usually constructed both the points are sharp and made of steel; 
but by having shifting points, it must be understood that one of 
the steel points is made capable of being withdrawn and re- 
moved, and its place may be supplied by either of two other 
points; one of which is a steel drawing-pen of the construction 
last described; and the other is a port crayon or tube for contain- 
ing a small piece of black-lead pencil. By the latter, circles can 
be drawn in pencil, — with the drawing-pen they are drawn with 
ink, — and v^hen the two sharp points are in the compasses they 
are equipped for scratching circles lightly upon paper, or measur- 
ing distances from the scale to the drawing, or vice versa. 

38. With the best compasses, a piece called a lengthening-bar 
is usually sold — this is a mere rod of m.etal, which can be fixed 
into the shifting leg of the compasses in the place of the points, 
any of which can in like manner be fixed to the end of the bar. 
Its use is to enable the compasses to strike circles of much larger 
radius than could be effected without it. 

39. In drawing large circles, the drawing-pen or pencil ought 
to be nearly vertical to the paper, to effect which, each of the 



OF DRAWING INSTRUMENTS AND IMPLEMENTS. 41 

drawing-points is equipped with a joint by which it may be placed 
in the required position. The French instrument makers gene- 
rally add another shifting point to their compasses, consisting of 
a very small revolving wheel, the edge of which is divided into 
points like a star. Its proposed use is to draw dotted lines, being 
supplied with ink for that purpose. It is, however, very diffi- 
cult to use, so as to produce a good and uniform line, and is very 
apt to make blots. The best means of producing a dotted line 
is first to draw it with pencil, or to make a faint scratch with the 
sharp point of the compasses, and then to pick in the dots with 
the fine point of a common quill pen. 

40. One pair of compasses with shifting points, will answer 
all purposes when expedition is not an object; but when this is 
the case, two pair will be necessary, viz. : one pair with shifting 
points as above described, and a smaller pair with fixed points, to 
be used for measuring only. The points of the measuring com- 
passes must be kept very sharp, for the double purpose of mea- 
suring off" small divisions on the scale with accuracy, and to 
avoid making large holes in the paper, which greatly disfigure a 
drawing. 

41. Compasses are occasionally made for the express purpose 
of measuring very minute distances with great accuracy, inso- 
much that they require to be used with a magnifying glass to in- 
spect their points. They contain a spring in one of their legs 
which tends to make that leg assume a slightly curved form, 
which can be made straight by turning a screw in that leg, so as 
to produce a more gradual and accurate motion of the points, in 
respect to their distance, than could be brought about by the 
direct application of the hand. Such compasses are called hair 
compasses, because they are intended to measure distances as 
small as hairs. For m.easuring such distances, steel spring divi- 
ders are, however, preferable and more certain. They are formed 
like other compasses, but instead of having a hinged joint, the 
two legs are united by a steel spring, the operation of which is 
to keep the legs separated or open, and they are brought together 
in any required degree by a long and fine screw fix^d to one leg 
and passing through the other, so that a nut upon this screw 
can be turned, and will place the points at any required distance 
with the greatest exactitude. 

42. The student should acquire the habit of using the com- 
passes with one hand only, not only because it looks better, but 
will prove much more convenient in practice. Both for measur- 
ing distances and drawing circles, the compasses should be held 
by their top joint, between the thumb and first and second finger 
of the right hand, and these same fingers will also open and shut 

6 



42 OF DRAWING INSTRUMENTS AND IMPLEMENTS. 

them very conveniently, without sujSering the left hand to touch 
the instrument. 

43. The marking-pointy ox pricker, is merely a very fine steel 
point for making a small dot through which lines are afterwards 
to be drawn, and is also useful in copying drawings, as will here- 
after appear. Such a point will generally be found concealed in 
the brass handle of the drawing-pen, if it is unscrewed about its 
central part. The points usually inserted by the instrument 
makers are by far too thick and coarse to be used, as they would 
produce large and unsightly holes in the paper. It is better 
therefore to withdraw this point, and to fix the pointed half of a 
fine sewing-needle in its place by sealing wax; or a convenient 
pricker can be made by so fixing such a needle in the end of a 
pencil or other cylindrical bit of wood. 

44. The protractor is a very useful and almost indispensable 
instrument, both for measuring angles already drawn, or for laying 
down such as it may be necessary to form upon the paper, with 
any required degree of magnitude. It usually occurs in two forms, 
a semicircle or a long parallelogram; but is occasionally made 
a complete circle, with a diameter running across it, and is form- 
ed of brass, ivory, boxwood, or thin horn, which is convenient 
on account of its transparency; but metal is generally preferred. 
It is nothing more than a semicircle divided into 180°, counting 
from the diameter, upon the middle of which the centre of the 
circle, from which the semicircle has been described, is marked. 
The divisions are marked with figures for the facility of counting 
them; and in large and accurate instruments, each degree is di- 
vided into two, three, or four equal parts, for measuring angles, 
to 30', 20', or 15'. When the protractor is laid down upon a 
parallelogram, it answers the purpose of a small ruler, and its op- 
posite side is usually filled with scales of equal parts to be next 
described. In this form the lower edge of the ruler is the diame- 
ter of the circle, and its centre is marked on the middle of this 
edge, while the other three edges are occupied with the divisions 
into degrees and their fractions. When the instrument is an en- 
tire circle, the circumference is divided into twice 180°, or two 
semicircles, each set of divisions beginning, as before, from tlie 
diameter. The only advantage of such a construction is greater 
accuracy; because, by extending the lines that form the angle, 
opposite angles may be measured; and as these should always be 
equal to each other, it afibrds an opportunity of measuring the 
angle both above and below the diameter, or of measuring the 
same angle twice over by the two opposite divided semicircles, 
and thus proves the accuracy of the divisions on the instrument, 



OF DRAWING INSTRUMENTS AND IMPLEMENTS. 43 

as well as insures greater precision in the measurement of the 
angle. 

45. The square protractor may, on the whole, be considered 
as the most convenient of the single arc instruments, not only be- 
cause it serves for a ruler, and may contain several useful scales, 
but the divisions, indicating the degrees of all angles less than 60°, 
are drawn to a longer radius than they could be upon a circular 
instrument, unless it is made very large; and consequently the 
measures of all such angles can be taken with greater accuracy. 

46. The protractor is sometimes very elaborately and expen- 
sively made, with an index, moveable by rackwork, and a ver- 
nier for measuring angles to single minutes. But such instru- 
ments are useless for the ordinary purposes of drawing, since the 
expansion and contraction of paper, with different states of hu- 
midity in the atmosphere, alters its dimensions to such an extent 
as to render every attempt at such extreme nicety nugatory and 
useless. Such instruments, consequently, are only useful for lay- 
ing down angles upon metals or substances less liable to change. 

47. The uses and application of the protractor, as well as of a 
scale, called the line of chords, usually engraved upon some part 
of this instrument, when of the square form, will be better un- 
derstood and explained when treating of angles in a more ad- 
vanced part of the work. 

48. Scales of equal parts, engraved upon brass, ivory, or box- 
wood, are highly necessary to all who undertake engineering 
or architectural drawing. They are merely parallel lines drawn 
upon the surface of a flat ruler, each line being divided into a 
certain number of equal parts, which parts are to be the repre- 
sentatives of larger portions of space in the real object, as before 
explained, see par. 14. The lines usually laid down are an inch, 
divided into tenths, and the tenth again divided into hundredths, 
two hundredths, and four hundredths of an inch, by the diagonal 
process. Also a set of simple lines, in Vv^hich an inch is divided 
into six, five, four and a half, four, three and a half, and three 
equal parts. Such scales are usually distinguished by the num- 
bers, 60, 50, 45, 40, 35, and 30, placed at their ends, which in- 
dicate that the entire inch is divided into this number of parts, 
for one of the small divisions is subdivided into ten parts, thus 
constituting the above numbers. This decimal mode of division 
is very convenient for all purposes of land surveying by the chain; 
but for architectural and engineering purposes, the extreme divi- 
sion must be subdivided into twelve instead of ten parts, because 
the dimensions are alwaj^s given in feet and inches. Any one 
division may, therefore, be taken to represent a foot, and the 
twelfth part of such division will be an inch. 



44 OP DRAWING INSTRUMENTS AND IMPLEMENTS. 

For the purpose of the Architect and Engineer this scale should 
be carried to larger dimensions than is usually done on the scales 
that are sold; for there should also be the following scales, half 
inch, three-quarters, one inch, one and a quarter inches, one and 
a half, one and three-quarters, two inches, two and a quarter, two 
and a half, two and three-quarters, and three inches, to a foot, one 
of each of these dimensions always being divided into twelve 
parts for inches, or into twelve parts on one side, and ten on the 
other, for the convenience of the chain operations of the land sur- 
veyor. The scale which the author has found most convenient, 
is represented by Fig. 3, Plate I., which shows its two sides, 
and for the convenince of such as may not possess the means of 
obtaining such scales, this figure may be cut out and pasted on 
a piece of smooth wood, and with care will last a long time. 

49. The above drawing instruments are absolutely necessary 
to the Civil Engineer, and they may always be procured, put up 
in small portable cases, under the name of, cases of drawing or 
mathematical instruments. Such case always contains what has 
been above enumerated, and sometimes other things, particularly 
an instrument called a sector, which has the appearance of a 
jointed ruler, with a great number of scales engraved upon it. 
The sector is for solving a number of problems in proportions, 
and in trigonometry mechanically by the compasses only, and is 
a highly ingenious and useful instrument, but to be really ser- 
viceable, it requires a greater degree of accuracy in workmanship 
than is usually bestowed upon it, and is always a high priced in- 
strument, although not always to be depended upon; and as all 
that it can do may be worked out with greater certainty and pre- 
cision by figures and formulae, it is an instrument seldom resort- 
ed to by practical men. Drawing instruments are always made 
four or six inches long. The six inch size are the most conve- 
nient for general use, and their price varies with the number and 
excellence of the instruments, or the metal of which they are 
composed. 

50. The following is a list of the articles which a good and 
complete case of drawing instruments should contain. 

A pair of hair compasses, or plain small dividers, with fixed 
points. 

A pair of compasses with shifting points, viz: their proper steel 
point, a point carrying a pencil, another carrying a drawing-pen 
for ink, and a lengthening bar to increase the radius. 

A bow pen with an ink point, and another with a pencil point, 
for drawing very small circles. 

A steel drawing-pen, with long brass handle, terminating with 
a rather blunt and round point, for copying drawings by camp 



OP DRAWING INSTRUMENTS AND IMPLEMENTS. 45 

paper, as hereafter described. The handle of this pen should 
contain a sharp steel point or pricker. 

A black-lead pencil, with a very thin brass top, the use of 
which is to clean between the cheeks of the drawing-pens, if the 
ink should become thick, and cease to flow freely. 

A steel file, for bringing the black-lead pencil to a very fine 
point. One end of this file terminates in a penknife blade for 
mending pens and cutting pencils. The other end is a key, or 
screw-driver, for adjusting the friction in the joints of the com- 
passes; because the joint of the dividers for measuring, should 
move very freely, while that of the large compasses for drawing 
circles should be rather stifi". 

A small parallel ruler. 

A sector and a protractor, either semicircular, or in the form 
of a ruler, in which last case the scales of equal parts, and a line 
of chords, are usually engraved on the instrument, (in addition to 
the radiating lines,) for measuring the degrees of angles. When 
a semicircular protractor is put into the case, a separate ruler is 
necessary for containing these scales. 

51. With the exception of the divided scales and ruler, all the 
above described drawing instruments are most conveniently com- 
bined in a very small and portable form, in what are called the 
Engineer's folding pocket compasses; an instrument of such 
utility, that it ought to be in the pocket of every Engineer. 
But as this instrument is not yet very common, a short descrip- 
tion of it may be useful. Its form is shown in Fig. 4, Plate I,, 
of the actual dimensions in which it is generally made. The 
instrument, when opened for use, has the appearance shown in 
the figure, and is nothing more than an ordinary pair of compasses 
with two sharp points, except that there is a joint in each leg at 
a and b, upon which joints the points turn inwards, so that they 
can both be put into the positions shown by dotted lines at c, 
when the compasses are closed or shut up, and then they may be 
carried in the pocket with as much safety as a pocket penknife. 
When the compasses are opened out, they are ready for taking 
measurements upon a drawing or from a scale, or for scratching 
circles. The two legs, d d, of the compasses are hollow tubes, 
and the joints a and b slip into those tubes and carry the other 
necessary points of the compasses. Thus, upon drawing the 
joint a out of its tube, a crayon socket and bit of black-lead pen- 
cil will be found in it, and by reversing this, or pushing the sharp 
compass point up into the tube, and leaving the pencil projecting, 
the compasses are prepared for drawing circles with pencil. The 
other joint b, in like manner, carries a drawing-pen for ink, so 
that by reversing this point we have compasses with an ink point. 



46 OF DRAWING INSTRUMENTS AND IMPLEMENTS. 

Either or both the joints may be wholly withdrawn from the 
compasses, and, if bent, the one becomes a bow pen with a pen- 
cil, and the other with an ink point; while, on the contrary, if 
the two shifting points are made straight, one can be used as a 
black-lead pencil, and the other as a drawing-pen for ink, while 
either steel point of the compasses may be used as a pricker: so 
that this little instrument combines in itself an entire case of in- 
struments, in the smallest possible space, and at about one-third 
of the cost that the instruments would amount to. As the legs 
of these compasses are not straight when quite open, and the 
points may be bent inwards, this instrument so used becomes a 
pair of calliper compasses, for taking the exact diameter of sphe- 
rical or cylindrical solids, being a measurement very frequently 
required by the Engineer. And as a small ivory scale, no larger 
than the compasses, containing lines of inches and equal parts, 
and a line of chords, may be made and put up in a case with a 
pair of these compasses, the Engineer possessing them will find 
himself equipped with all the instruments necessary for making 
every drawing on a small scale, where expedition is not an object. 
But in the office, larger and more expeditious instruments are of 
course desirable. 

52. There are many more instruments used in drawing, but 
they are not, like the foregoing, absolutely essential to the young 
Engineer. Some of these will, however, be described, when 
treating of the purposes for which they are particularly intended. 
For the present it will be sufficient to observe that a set of plot- 
ting scales is merely a set of ivory rulers, both edges of which are 
thin QY feather edged, and each edge has one scale of equal parts 
engraved upon it and divided decimally. Each ruler therefore 
contains two scales, and, consequently, the usual set of six rulers 
contains twelve different scales, the principal divisions of which 
are meant to represent chains, and the smaller ones links, as these 
scales are only used in maps or surveys of land. Each ruler is 
usually about a foot long; and as the divisions are upon the ex- 
treme edge, they are very useful and expeditious, both for draw- 
ing maps or plans of land, or for measuring such as have been 
previously made without the use of compasses, for the measure- 
ments are made by applying the scale directly to the paper. 

53. Beam compasses are for drawing circles or arcs of very 
large radius, which sometimes occur in making drawings, par- 
ticularly of bridges, and need never be used unless the radius is 
so long as to make it beyond the stretch or opening of common 
compasses. The beam compass derives its name from its mode 
of construction; for this instrument consists of a long and straight 
beam or bar of wood or metal, usually from one to four feet in 



OF DRAWING INSTRUMENTS AND IMPLEMENTS. 47 

length, with a steel point fixed at one of its ends at right angles to 
the length of the bar, to serve as a centre, and a sliding socket that 
moves along the bar, and can be fixed upon it by a milled screw 
at any required distance from the last mentioned point or centre. 
This sliding socket carries shifting points similar to those of 
other compasses, viz: a sharp steel point, a pencil point, and a 
drawing-pen for ink, so that these compasses may be used with 
the same facility as other compasses, both for measuring distances 
and drawing circles; and as the top, or one of the sides of the 
long bar, is graduated to inches and tenths from the fixed point 
or centre, any dimensions of radius may be very readily obtained. 

54. Should the student be desirous of tinting or colouring his 
drawings, he will require, in addition to the articles above enu- 
merated, a small box or case of water colours, with a few camel's 
hair brushes, or pencils, as they are generally called. Such 
colour boxes, with the colours in square cakes prepared for use, 
may be purchased in all large towns; and to use them, nothing 
more is necessary than to rub the end of the cake of colour in a 
few drops of clean water, previously applied by a brush on the 
surface of a common dinner plate, when a sufficient quantity of 
colour for present use will soon be obtained. About six cakes 
or varieties of colour will be sufficient for the purposes of the 
Engineer and Surveyor, and the most essential are light red, lake, 
Prussian blue, yellow ochre, gamboge, and burnt umber. Brick- 
work is generally coloured with light red, and any additions or 
alterations to it with lake. Pine timber is usually coloured with 
gamboge, and oak or hard timber with yellow ochre, or that 
colour mixed with burnt umber. Wrought iron is coloured with 
Prussian blue, and cast iron with that colour mixed with Indian 
ink, which is not mentioned in the above list, on account of hav- 
ing been referred to among the essentials. Brass is marked by 
either of the above yellows. In Plans, roads are tinted with 
burnt umber; water with Prussian blue; and all the various tints 
of green, both light and dark, for grass land, trees, hedges, and 
fields, may be obtained by making mixtures of Prussian blue 
with gamboge or yellow ochre, or with both. In fact, practice 
and experience will show the young artist that by combining or 
mixing the above six colours with Indian ink, in proportions that 
can only be ascertained by practice, he will be able to produce 
almost every tint he can require, for the white paper is always 
left to produce a light or white appearance. 

55. In locations where colour boxes cannot be procured with 
cakes of colour, the unprepared colours can generally be obtained 
in a state of powder at the drug stores; but, if used in this state, 
it is necessary to mix them with very weak gum water, or a solu- 



48 ON COPYING DRAWINGS. 

tlon of gum arable, instead of with simple water, or they will all 
rub off the paper as soon as they become dry. If the paper has 
from any cause become a little greasy, though not to such an ex- 
tent as may be visible, the colours will not lie or spread upon 
that part of the paper, unless a little of the gall of the ox is mixed 
with the water. Ox gall may be obtained at any slaughter- 
house, and if thinly spread upon the bottoms of dinner plates, it 
may be dried in the sun and will keep good as long as it is kept 
dry. When wanted, it is soluble in water, in which a little pot- 
ash or salt of tartar has been mixed. Infusion or solution of 
Spanish liquorice, and of tobacco, also make very good general 
brown tints, and are often resorted to even by artists in cities who 
have the command of every colour. 

56. In order to varnish a drawing to preserve it from injury, 
it must first be pasted down upon a smooth board, pasteboard, or 
piece of cloth tightly strained upon a frame. The whole face of 
the drawing must then be covered over thinly and evenly with 
strong gum water. Its strength should be such, that when dry 
it may produce a uniform gloss, or slightly shining effect over 
the whole drawing or print without cracking. The use of this 
gum water is to destroy the absorbent quality of the paper, and 
prevent the varnish from sinking into it; because, if it does so, it 
will discolour the paper and give it the appearance of having 
been greased with oil, and these stains cannot be removed, if once 
produced. When the coat of gum water is quite dry, one or two 
coats of white spirit varnish, or best copal varnish, may be laid over 
the gum, and the surface when dry will shine as if glass had been 
put over the picture; and should it become soiled, it may be 
washed with water at any future time, without fear of injuring 
it. Both the gum water and varnish should be laid on with a 
large soft brush; and wide flat brushes are made and sold for this 
express purpose, under the name of varnishing brushes. Var- 
nishing ought not to be attempted in cold damp weather, as the 
success of the operation depends in great measure upon the 
rapidity with which the varnish dries. It dries best in the sun- 
shine in open air, and if that cannot be obtained, the varnished 
piece ought to be set at a good distance from a fire in a warm 
room, until it is quite dry. 

57. Having so far explained the use of the instruments or im- 
plements to be used in drawing, our next attempt will be to 
give the student some insight into the manner of copying draw- 
ings, for this is an occupation that generally falls to the lot of the 
assistants in the Engineer's office, and it is of great importance 
that facility, accuracy, and expedition, should be acquired in this 
branch of business. 



ON COPYING DRAWINGS. 49 

Drawings are copied by various processes thus, — the copy is 
made of the same size as the original: 

1st. By eye inspection and measurement. 

2ndly. By pricking through, and drawing from one point to 
another; and 

3dly. By the aid of tracing, or tracing-paper, and camp-paper. 

Drawings are copied of greater or less dimensions than the 
original. 

4thly. By eye inspection, and proportional measurement, 
which is most easily effected by an instrument called i\iQ propor- 
tional compasses, hereafter described. (93.) 

5thly. By proportional squares; and 

6thly. By an instrument for the purpose, called a Panta- 
graph. 

The first and fourth processes of copying drawings are of the 
highest character, as requiring more skill and attention than any 
of the others, and are those in which the young draughtsman 
ought particularly to practise himself; because when he has ac- 
quired facility in this kind of drawing, he will experience no 
difficulty in any of the others. 

58. In the first kind of drawing, it is understood that the 
draughtsman having prepared his paper on a drawing-board, sets 
the original before him, and by looking at it, and taking certain 
measurements from it, that he is to produce a fac-simile not only 
as to appearance, but to measurement and every other particular. 

Suppose the drawing to be copied is a building, it will first be 
necessary to draw a horizontal line near to, and parallel with, the 
bottom of the paper, to represent the base of the building or place 
where it touches the ground. Then the distances of the upright 
corners of the house from each other, and from the sides of the 
paper must be measured on the original with compasses, and those 
distances be transferred to the horizontal line. Upon each of 
these points, perpendiculars to the base must be raised, and this 
may be done by the triangular square or T square. (30 and 31.) 
The positions of the two sides of each window and door are ob- 
tained and laid down in the same manner, and long pencil lines 
drawn to indicate their relative positions in respect to the hori- 
zon, without any regard to their height. Next the heights of all 
the windows must be measured and transferred in like manner, 
and lines ruled through all these points parallel to the first hori- 
zontal line. This may be done by the square or T square, apply- 
ing its stock to the side of the drawing-board, and the top hori- 
zontal line of the building is so obtained. Next come the sloping 
lines of the roof, which are not parallel to either side of the 
drawing-board, and consequently cannot be obtained in the same 
7 



50 ON COPYING DRAWINaS. 

way. To get the direction of these lines, the angles they make 
with each other, or with other lines previously obtained, must be 
measured by the protractor, and are transferred by laying down 
similar angles on the copy by its means; or they may be trans- 
ferred at once by using the T square with a shifting stock. (31.) 
This slight view of this kind of drawing will convince any one 
that some knowledge of geometrical figures will greatly facilitate 
the progress of the learner — and such knowledge, it is to be pre- 
sumed, has been previously obtained by those who embark in the 
Engineering profession. But as mathematical principles are 
generally taught in schools and colleges with chalk on the black 
board, and precepts rather than mechanical accuracy are alone 
aimed at, drawing instruments and that precision of measure- 
ment requisite in good mechanical drawing are wholly neglected. 
Notwithstanding, therefore, the principles of the few examples 
about to be offered must be obvious to most persons who will take 
up this volume, yet the practical operation of working or con- 
structing them on paper with care and precision is strongly re- 
commended to air students as a useful exercise. The examples 
are few, and are only such as are likely to occur in constructing 
original drawings, or in copying representations of things by the 
first and fourth methods of copying before referred to, viz: that 
of simple inspection and measurement. The methods of drawing 
or constructing curves, and many other geometrical figures, will 
be given in the course of the work, but it was thought better to 
describe them where their applications occur, than to enlarge the 
present chapter with subjects, the use of which would not now 
be apparent. 

59. No demonstrations either of the problems immediately 
following, or of those that occur in other parts of the work will 
be given. They would swell its dimensions very unnecessarily, 
because it does not profess to teach mathematical principles, but 
only to show some of their applications. Mathematical know- 
ledge must be derived from other sources, and if it is possessed, the 
addition of the demonstrations will form an agreeable praxis for 
the student, and may be insisted on or not at pleasure by the 
Teacher who uses the book. 



ON COPYING DRAWINGS. 51 



USEFUL PRACTICAL PROBLEMS IN GEOMETRY. 

Problem I. — Fig, 5, Plate I. 

60. To divide a given line Jl B, into two equal parts, with- 
out the loss of time attendant on making w^any trials with the 
compasses to find its central point. — From the points A and B, 
(or ends of the given line,) as centres, and with any opening of 
the compasses, greater than half the length of the line, describe 
arcs of circles, cutting each other in c and d. Draw the right 
line c d, and the point e, where it cuts A B, will be the middle 
required. 

Problem II. — Fig. 5, Plate I. 

61. To raise a perpendicular on the centre of a right line. 
— This operation is precisely the same as the last, although with 
a different object. Because the point e is the centre of the line 
A B, and the new line drawn through the two points of intersec- 
tion c and d, will not only cut the line into two equal parts, but 
will be perpendicular to it at its central point e. 

Problem III. 

^2. To raise a perpendicular on any given point of a line 
*B. B, such point not being the centre of that line. — This is an- 
other instance of the same operation; for, although the given 
point is no longer supposed to be in the centre of the given line, 
yet we must make that point the centre of a short portion of the 
given line selected for the purpose. Thus, Fig. 5, Plate /., 
suppose A B to be the given line, and that this line is unevenly 
extended at its two extreme ends, so that the given point e, shall 
no longer be in its centre. The first operation must be to mea- 
sure and set ofi* two equal distances, e A and e B, upon the 
given line, by which the points, A and B, are obtained; and these 
points are now used as centres for describing the arcs and obtain- 
ing the intersections c and c?, when the proceedings are as in the 
two last problems. 

Problem IV. — Fig. 6, Plate I. 

63. To raise a perpendicular upon the extreme end of a line. 
— Let C D be the given line, and D the point upon which the 
perpendicular is to be raised. Select any point, /J at a moderate 
distance above the line, and from the end D. Then with radius 
y D, describe the arc ^ D A, touching the end of the given line 
at D, and cutting it at h. From the intersection at h, draw the 



52 ON COPYING DRAWINGS. 

line h g, passing through the point f, and continue it until it in- 
tersects the arc at g. Then through the points g and D, draw the 
line i J), which will be the perpendicular required. 

Problem V. — Fig. 7. 

64. From a given point, out of a line, to let fall a perpen- 
dicular upon that line. — Let k be the given point, out of the 
line E F. From the point k, with any radius greater than its dis- 
tance from the line E F, describe the arc / m, intersecting the 
line at these points, and from them, with any convenient radius, 
describe two other arcs below the line which cross each other at 
n. Lastly, draw the line k o from the given point, through the 
intersection at n, and it will be the perpendicular required. 

Problem VI. — Fig. 8. 

Q5. To draw an angle equal to another that is given. — Let 
r s t hQ the given angle, and upon its point, or apex 5, as a centre, 
with any convenient radius describe the arc ^' z^, cutting both 
legs or lines of the given angle. That done, draw a line z y, in 
any position, to be the representative of the line t s, in the given 
angle, and fix the point 3/, which is to be the apex of the new angle 
about to be produced; on this point as a centre, with radius s v, 
describe an arc a b; measure the chord or distance v w, and trans- 
fer that distance from a to the arc at b, and it will give a point b, 
through which draw the line x y, and the new angle will be 
complete. 

Problem VIL 

66. To divide a right line into a required number of equal 
parts, without the loss of time attendant upon stepping over it, 
(probably many times,) with the compasses, for that purpose. 
— Let G H, Fig. 9, be the given line, which is required to be 
divided into seven equal parts. From G, draw a line G- p, making 
an acute angle with the line G H; then from H, draw another 
line H q, making an equal angle with the first, but on the oppo- 
site side of the given line; then, with any convenient opening of 
compasses, set off the required number of equal divisions upon 
either or both of the lines Gc p, or H q, as at 1, 2, 3, 4, 5, &c., 
commencing from the angular points G or H: join the last of 
such divisions to the end of the given line as by the line 7 H, 
and rule lines parallel to this first line, through each of the divi- 
sions 6, 5, 4, 3, &c., and the points where these parallel lines in- 
tersect the given line G H, will be the equal divisions sought. 



ON COPYING DRAWINGS. 53 

Problem VIII. 

67. To measure and transfer any angle by the Protractor, 
(42.) — Cause the diameter of the protractor, or the edge that 
carries the centre of its circle, to coincide exactly with either of 
the lines forming the angle to be measured. Shift the instrument 
laterally, until the point, or mark, that indicates the centre of the 
circle, touches the apex of the angle, when the other line of the 
angle will be found projecting beyond the graduated edge of the 
instrument, and the division and number that lies immediately 
over that line, wall be the measure of the angle. 

Note. — In practice it frequently happens that one of the lines, 
or legs of the angle, may not be long enough to project beyond 
the instrument, which will, therefore, hide it from view. In 
such case, that line must be carefully lengthened with a pencil 
and ruler, until it can be seen. This will not disturb the accu- 
racy of the operation, since the lines, which form angles, may be 
indefinitely long or short, without affecting the measure of the 
angle, while their relative position remains unchanged. 

In order to copy, or transfer, any given angle by means of the 
protractor, that angle must first be measured, as above described. 
A line must be drawn to represent one side of the angle, and the 
position of its apex must be fixed in such line. The centre of the 
protractor is then placed over the apex, its diameter is made to 
coincide with the line, and a dot, or mark, must be made against 
that division, which before marked the measure of the angle. The 
itstrument is now removed, and a line being drawn from the dot 
to the point fixed for the apex, will produce the similar angle re- 
quired. 

Problem IX. — Fig. 8. 

68. To measure and transfer any angle by a line of chords. 
— A line of chords is usually engraved on some of the scales be- 
longing to drawing instruments, (see Fig. 3,) and its use may 
be explained by Fig. 8. Instead of drawing the arc v w with 
random radius from centre s, we must, when using the line of 
chords, take the distance from to 60° upon the scale in our com- 
passes, and strike the arc v w with that radius. Then measure 
the chord or distance between v and w, and transferring that dis- 
tance from the commencement of the scale, the number of divi- 
sions in that space will be the measure of the angle. 

To transfer or lay down any given angle, the same process 
must be resorted to in a different order, viz: Draw the line z y.^ 
and upon its end y, as centre, with radius of 60°, taken from the 
scale, describe the arc a b. Then measure off the required num- 
ber of degrees for the angle upon the scale, and transfer it to the 



54 ON COPYING DRAWINGS. 

arc from a towards h, and thus the point h will be obtained, 
through which and the point y draw the line x y, and the angle 
required will be produced. 

Problem X. — Fig. 10. 

69. To bisect or divide a given angle c d e into two equal 
angles. — From the point d, with any radius, describe the arc c e. 
From intersections c and e with the same, or any other radius, 
describe arcs cutting each other inf. Draw a line through ^and 

f, and it will bisect the angle c d e,2is required. 

Problem XI. — Fig. 11. 

70. Through a given point g, to dratv a line parallel to a 
given line h i. — Assume any point k in the given line h i, taking 
care that it is not immediately above or below g, but at a con- 
venient lateral distance from it. Then upon points g and k as 
centres, with radius g k describe the arcs k I and g m; make these 
two arcs equal in length, which will fix the point /, through 
which and g draw the line I g, which will be parallel to h i, as 
required. 

71. When the new parallel is to he at a given distance from 
the given line n o, Fig. 12. — Assume two or more points, jt? q, in 
the given line; then with radius j» r equal to the required distance 
of the two lines, describe as many arcs upon points p q, and as 
centres, as may be necessary. Make the line r 5 a tangent to 
all these arcs, and it will be parallel to the given line. 

The operation of the common parallel ruler is referable to 
this principle. 

Problem XII. — Fig. 13. 

72. Upon a given line t v, to construct an equilateral tri- 
angle. — Upon the points t and v, being the ends of the given 
line, and with radius equal to t v, describe two arcs, cutting each 
other in w; draw t w, and v w and t v w will be the triangle re- 
quired. 

Problem XIII. — Fig. 14. 

73. To find the centre of a given circle, or of one already 
described. — Draw any chord u x and bisect it with a perpendicu- 
lar y z, running quite across the given circle; bisect this per- 
pendicular as at a, and that point will be the centre required. 

Problem XIV. — Fig. 15. 

74. To draiv a circle through any three given points, pro- 
vided they are not in a right line. — Join the three given points 



ON COPYING DRAWINGS. 55 

b, c and d by right lines, and upon the centre of each of such lines 
erect perpendiculars, (Prob. II.) which will intersect each other 
in e, the centre of the circle; therefore, from e as centre, with 
radius e b ov e c, &c., describe the circle required. 

Problem XV. — Fig. 16. 

75. To describe the segTnent of a circle of any required length 
and height, — Draw the line, f g equal or proportionate to the 
required length of the segment, and bisect it by the perpen- 
dicular k h. Set off the required height from i to k in this per- 
pendicular, and join k f Bisect k fhy the perpendicular / h, 
continued until it intersects k h, when the point h will be the 
centre from whence to describe the segment y A: ^, with radius 
equal to hf 

Problem XVL—i%. 17. 

76. To draw a tangent to a given circle that shall pass 
through a given point m. — From the centre n draw the radius 
n m, and through the point m draw op perpendicular to n rriy 
and it will be the tangent required. 

Problem XVII.— i^z^. 18. 

77. To draw a tangent to a circle or segment at any given 
point q, when the place of the centre is not known. — Measure 
off any two equal arcs q r, r s, upon the circle beginning from 
the given point q, and draw the chord q t s. From q as centre, 
describe the arc t r v with radius q v, make v r equal to / r, and 
through V and q draw the line r q u, which is the tangent re- 
quired. 

Problem XVIII. —i^z^. 19. 

78. To describe a regular octagon in a given square w x y z, 
— Draw the diagonals xy and w r, intersecting at a. Upon the 
four points w, x, y and z as centres, with radius w «, describe 
the arcs b a c, d a e,f a g, and h a i. Join i b,d g,c h and ef 
and thus form the required octagon. 

Problem XIX. — Fig. 20. 

79. In a given circle, to describe any regular polygon. — 
Divide the circumference of the circle into as many equal parts 
as there are sides in the polygon to be produced, as at k, I, m, n, 
o,p, and unite these points by right lines, when the figure will 
be complete. 

80. Note. — This is called a polygon inscribed in a circle. If 
a circumscribed polygon is required, or one constructed round 



56 ON COPYING DRAWINGS. 

the outside of the circle instead of within it, draw radial lines 
from the centre of the circle through each of the points A:, /, 7n, 
&c., letting them project beyond the circle; then draw lines from 
one of these radii to the other, parallel to the sides of the in- 
scribed polygon, and touching the circle like tangents, when a 
circumscribed polygon will be produced. 

The inscribed hexagon requires no division of the circle, be- 
cause radius may always be taken for one side of the polygon. 

For an easy mechanical process of setting out polygons, see 
JProportional Compasses, near the end of the present section. 

Problem XX. — Fig. 21. 

81. To make a triangle whose sides shall be equal to three 
given lines q r s, any two of them, being greater than the third. 
— Draw t V equal to the line q. Upon t, with radius equal to 
the length of line s, describe the arc u w; and upon v, with radius 
equal to the line r, describe another arc x u, intersecting the first 
arc in u. Join u and t and u and v, and t u v will be the tri- 
angle required. 

Problem XXl.—Fig\ 22. 

82. To Tnake a trapezium, abed, equal and sirnilar to 
another given trapezium^efg h. — Divide the given trapezium ef 
g h into two triangles by drawing the diagonal e h; make c d equal 
to g h. Upon c d construct a triangle a c d, equal and similar 
to the triangle e g h, (by the last problem,) and upon a d, which 
is equal to e h, construct the triangle a b d, equal and similar to 
efhf and the figure abed will then be produced, which is the 
trapezium required. 

Note. — This is a most useful and important problem, as by its 
means any plan may be copied; because every figure, however 
irregular, may be divided into triangles, and it is in this way that 
the irregular forms of fields in land surveying are measured and 
their quantities computed. 

Problem XXll.—Fig. 23. 

83 . Two right lines being given, to find a third proportional 
thereto. — Let AB and CD be the two given lines; make an angle 
HEX at pleasure; from E make EF equal to AB, and EG equal 
to CD, and join FG; make EI equal to EF, and draw HI pa- 
rallel to FG, then EH will be the third proportional required; 
that is, EF : EG :: EH : EI, or AB : CD :: CD : EI. 

Problem XXIII. — Fig. 24. 

84. Three lines being given, to find a fourth proportional. 



ON COPYING DRAWINGS. 57 

— Let AB, CD and EF be the three lines given. Draw GH and 
GI, making any angle HGI; make GH equal to AB, GI equal 
to CD, and draw HI. Make GK equal to EF; draw KL through 
K parallel to HI; then GL will be the fourth proportional re- 
quired; that is, GH : GI :: GK : GL, or AB : CD :: EF : GL. 

Problem XXIV. ~i^/^. 25. 

85. To find a mean proportional between two lines given. — 
Let AB and CD be the two given lines. Prolong AB by the 
length of CD; or draw a new line EF equal to AB, and prolong 
it from F to G by a quantity equal to CD. Bisect this compound 
line as at H, and from H as centre, with radius HE or HG, de- 
scribe the semicircle EIG; and lastly, raise a perpendicular on 
the point F, (where the two lines meet,) cutting the semicircle 
at I, when the line FI will be the mean proportional sought. 

86. When the student has acquired a facility in working the 
above problems, it is presumed he will find no difficulty in copy- 
ing drawings by the first process before referred to, (57,) or even 
in making original drawings, because the above rules will furnish 
the means of producing all such forms as usually occur in draw- 
ings, with the exception of the ellipse and some other curves 
that occur in the arches of bridges and formation of tunnels, and 
which will be described in that part of this work which treats 
upon those subjects. 

87. The second process of copying drawings of the same size 
and appearance as the originals, by pricking through them, is so 
simple as to need no description; but a few observations upon the 
mode of executing it may be useful. It requires no skill; and 
from its facility and the expedition with which copies are made 
by its means, it is the method most frequently resorted to in the 
ofiice of the Engineer and Architect. 

The sheet of paper intended to receive the copy must be pro- 
perly stretched upon a drawing-board, (20,) and the print or 
drawing to be copied has to be laid over it in a proper position, 
so as to bring that which has to be drawn fairly into the middle 
of the prepared sheet of paper. That done, lead weights (31,) 
must be disposed at the corners, sides, and other parts of the 
copy which contain no part of the figure, for the purpose of re- 
taining it securely in its place. The paper, or paper and drawing- 
board, should be rather larger than that which has to be copied; 
not only to prevent injury to the original, but likewise to admit 
of pencil marks being made in several places on the extreme edges 
of the original, half of them being upon it, and the other half 
upon the paper below. These marks are quite essential, and 
should be made with great care and accuracy. Their use is to 
8 



58 ON COPYING DRAWINGS. 

indicate whether the original has shifted from its place during 
the process of copying; a circumstance that must be carefully 
guarded against, because, should it happen, the work will be 
spoiled, unless the original is brought back to its first position, 
which may be accurately done by these marks; and likewise to 
permit the draughtsman to examine his work in progress, by oc- 
casionally lifting up the original. This should never be done, 
except on suspicion of a mistake or for some cogent reason; and 
if the marginal marks are not made, all the former labour will 
be thrown away, as the original can never be correctly reinstated 
in its former position. 

88. The original drawing having been properly placed over 
the paper, the pricking may commence. This, as before ob- 
served, should be done by a fine sewing needle, fixed in a handle, 
(43). A hole must be pricked through every angle and intersec- 
tion of lines in the original drawing; but circles, or parts of them, 
should never be pricked, if their centres are known. Marking 
the centre is sufficient and better, and afterwards putting in the 
circles with compasses by actual measurement; but all irregular 
curves that cannot be drawn with compasses must be pricked at 
regular small intervals. If the centre of a circle is not marked, 
three dots made in its circumference will be sufficient for finding 
the centre by Problem XIV. During the whole operation the 
needle should be held vertically, to insure that the holes in the 
paper shall be exactly under the corresponding points in the ori- 
ginal. In pricking a drawing, the draughtsman must not run 
from one part of the original to another; because if he does so, 
he will get into confusion, and probably leave many essential 
points unmarked. A regular system of work should therefore 
be adopted; and the best is to divide the original into horizontal 
stripes, either by ruling lines across it at every one, two, or three 
inches apart, according to the intricacy of the drawing, or else 
to place a flat ruler upon the drawing, exposing a certain quantity 
above it, and then to begin at the left hand top of such space and 
proceed regularly to the right hand side, taking care to mark 
every important part as it occurs in that space. After examining 
it carefully to see that every point is marked, the ruler may be 
shifted downwards to expose a new strip, and that must be gone 
over from left to right in like manner; and so on until the whole 
drawing is marked, when the original must be taken up and 
placed before the draughtsman, who now has to find out the marks 
he has been making on his paper, and their correspondence with 
each other and with the original. Some difficulty frequently 
occurs in finding the marks at first, because if they are not very 
fine and small they will disfigure the drawing; but as soon as a 



ON COPYING DRAWINGS. 59 

few lines of connexion are drawn among them, that difficulty will 
vanish. The first lines of connexion are best drawn by hand, 
with a very soft lead pencil, and they should be very faintly 
marked, as errors often occur in the first union of the points; but 
so soon as the general outline of the figure is got in, the places of 
the points will become obvious, and the drawing-pen and ruler 
may be resorted to for putting in every thing in its proper place. 

89. It need scarcely be observed that, if more than one copy 
of the same drawing is required, the pricking may take place 
through two, or even three sheets of paper, properly fixed down, 
at the same time, by which much time and labour will be saved. 
When the original is done with, it should be laid with its face 
downwards upon a smooth drawing-board, and the burs of the 
holes made in pricking be rubbed down with the back of the 
thumb nail. This will close the holes so effectually as to make 
them almost disappear. The same operation must be performed 
upon the copied drawings, after the principal lines are got in and 
the holes are done with. 

90. The third process for copying drawings of their Veal size 
is by tracing-paper, and this is very frequently resorted to on 
account of its expedition, when the beauty of the copy is not re- 
garded, and the artist merely wishes to preserve a copy for his own 
use. Tracing-paper is large and thin paper, rendered transparent 
by being coated with some oil or varnish, and kept until perfectly 
dry, so that one sheet will not adhere to another. It is sold in 
such stores as provide drawing implements, and generally at a 
much higher price than its production warrants. It may be very 
well made by providing large and tough thin paper, and anoint- 
ing it as thinly as possible on both sides with cold drawn linseed 
oil, applied with a rag, and afterwards hanging up the sheets 
separately by one corner pinned to a line. The superfluous oil 
will drip off from the lowest angle, and in a few weeks of fine 
summer weather the sheets will become sufficiently hard and dry 
for use, and may be kept flat in a portfolio. Good tracing-paper 
will receive the marks of pencil, ink, and even colours, without 
difficulty. 

91. To copy a drawing by tracing-paper, nothing is necessary 
but to fix it in a flat position by a drawing-board or lead weights, 
placing a sheet of tracing-paper over it. That paper should be 
so transparent as to permit every line and mark of the smallest 
kind in the original to be seen through it, consequently all such 
marks can be traced or gone over with a black-lead pencil or pen 
and ink; which done, the tracing paper is removed, and will be 
a fac simile of the drawing copied. Having a tracing, it furnishes 
the means of producing a finished drawing at any future time. 



60 ON COPYING DRAWINGS. 

because the tracing can be strained over a clean sheet of paper, 
and be pricked through like any other original drawing. Or it 
may be transferred to the clean sheet without pricking, by what 
some writers call cmnp, and others transf erring-paper. 

92. Transferring-paper is thin paper, like that used for tracing, 
but not prepared with oil or varnish; one side of it is rubbed 
over with a solid lump of black-lead, or of red or black chalk, 
which must afterwards be sufficiently wiped off again to prevent 
its soiling the paper on which it is laid. A sheet of paper so 
prepared is laid with its coloured face downwards upon the paper 
strained to receive the copy, and the tracing placed above all, 
when the whole must be kept in their places by weights. The 
lines of the tracing are next gone over by an ivory point, or the 
obtuse end of the iDrass drawing-pen, which is prepared for that 
purpose, (50,) using sufficient pressure to cause the black-lead or 
other pigment that has been put upon the transferring-paper to 
leave marks or corresponding traces upon the paper which is to 
receive the copy. A perfect drawing cannot be obtained in this 
way, but a fac simile as to proportion and position will be pro- 
duced, in a sufficiently accurate manner to enable the draughts- 
man to finish it up, from the original, with much less labour than 
would otherwise be required. 

93. Camp-paper is only a variety of transfer-paper, prepared 
with lamp-black ground up with hard soap, and is used in the 
manner above described: but inasmuch as the lines j^roduced by 
it are black and appear like those of a copperplate print, and can- 
not easily be effaced, this paper is never used when the copy 
has to be worked up and finished by hand so as to produce a 
perfect drawing. 

94. When drawings or prints have to be copied of a different 
size from the original, whether larger or less, it will be evident 
that none of the above described processes can be resorted to. 
The first and most difficult mode of proceeding in this case, is by 
eye-inspection and proportional measurement. This kind of 
drawing has its foundation in what are called in geometry, simi- 
lar and proportional figures; because the enlarged or diminished 
representation must contain all the same parts as the original, and 
all these parts must be in the same ratio, or proportion to each 
other, that they bear in the original. Of course, no assistance can 
be rendered to this kind of drawing; but each line and part must 
be laid down in succession, by separate measurements. The 
easiest way of proceeding is to use two scales of equal parts, (48,) 
one fitted to the original, and the other to the copy to be made. 
Thus, if the original is made to a scale of one inch to a foot, and 
we desire a copy of half size, or double size, we must use scales 



ON COPYING DRAWINGS. 61 

accordingly. The length of each line, in the original, must be 
taken with compasses, and transferred to an inch scale, to deter- 
mine its value; that done, the same quantity has to be sought in 
the half inch or two inch scale, as the case may be, for the length 
of the line that is to represent the first. In like manner, all lines 
that make angles with each other, must have those angles mea- 
sured and transferred, by some of the rules herein before given, 
so that there is nearly as much trouble in copying a drawing to 
new dimensions, as in making an original one. 

95. If a drawing has to be diminished to half, or increased to 
double the dimensions of the original, the operation is much fa- 
cilitated by a kind of double pointed compasses, called TVholes 
and Halves. They are formed exactly like common compasses, 
except that instead of terminating, as they do, in a head or joint, 
they have opposite legs and points beyond the joint, or, in 
other words, the joint is intermediate between tw^o pair of com- 
passes, formed by two rods of metal, crossing each other at the 
joint. One pair of legs is made exactly twice as long as the 
other, consequently in opening and shutting them, the points of 
the long legs will move through exactly twice the quantity of 
space that the short ones do, so that if they are used to diminish 
a drawing to half its size, all dimensions are taken from the origi- 
nal, by the long pair of legs, and those dimensions are transferred 
to the copy by the short legs. On the contrary, when using the 
instrument to enlarge a drawing, the points are used in an exact- 
ly opposite manner. 

96. The most useful and convenient instrument for copying 
drawings, with varied dimensions, is the Proportional Compasses, 
the most approved form of which is given at Fig. 26 oi Plate I. 
They consist of two steel points a a, attached to two flat cheeks 
of brass or silver, b c. These cheeks, and the steel points, are 
both exactly alike in form and dimensions, so that they coincide 
perfectly when laid Over each other, d dd dls a long perforation 
made through both the metal cheeks, and in which a double 
sliding piece e, of a peculiar construction, slides freely from one 
end to the other, and can be fixed in any required position by the 
milled screw/". The peculiarity in the construction of the cen- 
tral sliding piece e is, that although it slides freely in the long 
perforation d d, which is dovetailed, to prevent separation of the 
two plates, and can be fixed in any required position by the 
milled head/; still, when so fixed, it does not interfere w^ith the 
free motion of the two cheeks, b and c, over each other, when 
they are moved upon the screw/, as a pivot or centre of motion, 
consequently the two points a a, can be used like those of a com- 
mon pair of compasses. The two points g g, are of steel, and 



62 ON COPYING DRAWINGS. 

are two other points of these compasses, and It will be evident 
that if the pivot f is brought into such a position that it shall 
stand exactly half way between the points a a and^^, equal de- 
grees of motion will take place at both ends of the compasses 
whenever they are moved. If, again, the pivot is so placed that 
its distance from g g shall be exactly half that from a a, then the 
instrument becomes a pair of Wholes and Halves, like those last 
described. As, however, the pivot has no fixed place but that which 
is assigned to it for the time being, it is evident that by duly 
placing it in respect to distance between the points a a and g g, 
every possible proportion, between the opening of the two sets 
of points maybe obtained; and, consequently, dimensions may be 
taken, and drawings copied by this instrument in every required 
proportion to each other that the range of the instrument admits of. 

97. To insure the proper placing of the central pivot to pro- 
duce these effects, one side of one of the cheeks is divided into a 
number of unequal parts, numbered 1, 2, 3, 4, 5, 6, &c., and 
headed lines; and a line is engraved upon the sliding piece e, 
w^hich has to be brought into coincidence with such of the divi- 
sions as may be required, keeping in recollection that when the 
mark is set against No. 1, the joint is in the common centre of 
the whole instrument, and the legs of both the compasses are of 
equal length. When set against No. 2, their respective lengths 
are as 1 to 2, consequently the instrument will be prepared for 
making a copy of half the size, or double the size of the original. 
When against No. 3, No. 10, or any other number, the respec- 
tive lengths of the legs will be as 3 to 1, or as 10 to 1, and so 
forth; and, consequently, will give lengths at the two ends pro- 
portionate to such numbers. 

98. The opposite side of the cheek, that is divided for lines, 
carries another engraved scale of more nearly equal parts, headed 
ciixles, the lowest division of which is numbered 6, and corre- 
sponds with No. 1, on the opposite scale. This scale is for the 
purpose of producing regular polygons of from six to fifteen sides 
and angles; and to use this scale, set the mark upon the slider e, 
opposite that number in the scale marked circles, which agrees 
with the number of equal parts into which any circle has to be di- 
vided. Then take the radius of that circle between the points 
a a, and the points g g will be at the right distance for stepping 
round the circumference of the circle, to divide it into the required 
number of parts. 

99. The instrument is complete as above described; but in 
using it, there is great danger of the points, (especially the longest 
ones,) getting shifted from their places, in handling and transfer- 
ring the distances. To remove this inconvenience, all the best 



ON COPYING DRAWINGS. 63 

proportional compasses have, in addition to the parts already de- 
scribed, a fixing bar and adjusting screw, shown at A, i, k, n, in the 
figure. By releasing the small screw at n, the points a a are free to 
move for taking any dimensions. Having obtained it, the screw 
n is tightened, which renders the points immovable, except by 
the milled head h^ connected with a fine adjusting screw z, by 
which the points may be adjusted in distance with the greatest 
nicety. When the instrument is not in use, the screw ?z is taken 
out and placed in a hole for the purpose, in the centre of the prin- 
cipal nut /j and the adjusting bar is carried with it and fixed 
parallel to the cheeks, when shut up, so that the instrument then 
assumes a very compact and portable form. 

100. Great care is necessary in the use of this instrument, that 
none of its four points may be broken; for if this should happen, 
they cannot be re-sharpened, as in common compasses, without 
destroying the proportional length of the legs of the instrument, 
and rendering the divisions upon the cheeks useless. The broken 
point must be lengthened by a competent workman before the 
instrument can again become useful. 

101. A less laborious, and more common method of altering 
the relative magnitude of drawings when copying them, is to 
make use of proportional squares, a process well known to, and 
much used, by artists of all denominations. It consists in 
covering the original that has to be copied, with small squares 
produced by drawing a number of equidistant lines parallel 
to each other, and to the top or bottom of the picture, and 
crossing these by similar lines at right angles to the first. 
The size of these squares must be regulated by the mag- 
nitude of the picture to be copied, and the intricacy of the ob- 
jects it represents. Having prepared the original with such 
squares, the paper intended for the copy must be prepared in the 
same way; that is to say, must be crossed by the same number of 
lines, and be thereby divided into the same number of squares. 
If the copy is to be of the same size as the original, then the 
squares upon both must be of the same size. If, on the contrary, 
the copy is to be diminished to one half, or one quarter, or in 
any other proportion, the squares upon the copying paper must 
be one half, or one quarter, or in the required proportion, less 
than the size of the squares on the original; while, if the copy 
has to be enlarged, the squares for copying must be made as much 
larger than those upon the original, as the dimensions of the copy 
are meant to exceed it. In all cases each line upon the original 
must have a number placed against it, beginning from left to 
right at the top, and from top to bottom at the side of the picture, 
and the corresponding lines upon the copying paper must be 



64 ON COPYING DRAWINGS. 

marked with corresponding numbers. Things being thus pre- 
pared, the draughtsman sets the original before him, and noticing 
all lines or marks that occur in the first square, or that formed 
by the intersection of the lines Nos. 1 and 1, he inserts those 
same marks in the corresponding square of his copy. The square 
formed by the vertical lines 1 and 2, and horizontal line 1, is 
next copied in, and so of all the others in succession, until the 
entire copy is made. 

102. When inserting the lines or marks into the copy, great 
attention must be paid to placing them in the same relative posi- 
tions in the copy square that they occupy in the original one. 
Thus, if a line occurs in the middle of any square in the original, 
it must be placed in the middle of the corresponding square of 
the copy. If near the top, bottom, or side of a square, a similar 
position must be given to it when transferred, and thus will the 
relative position of every part be preserved. These relative posi- 
tions may always be guessed at by the eye without measurement, 
if the squares are sufficiently small; and should that not be the 
case, the squares must be diminished by drawing intermediate 
lines through them, either in one or both directions, so as to 
divide each square into two parallels, or four smaller squares: but 
those who cannot thus divide by eye may use compasses. Nei- 
ther is it necessary that the original and copy should be covered 
with exact squares for parallelograms or rectangles, the sides of 
which are not equal, for even mere parallel lines will in many 
cases suffice for producing copies. This rule must, however, be 
attended to, that in whatever manner the original is divided, the 
copy must be divided in the same manner, and in the same pro- 
portion one part with another, and into the same number of parts, 
otherwise the copy will become a distorted instead of a correct 
resemblance of the original. Engravers and others who have to 
copy and reduce a great number of pictures, usually provide 
themselves with slight wooden frames, divided into squares by 
threads stretched across them. Such frames not only save the 
time that would be occupied in dividing the original and drawing 
squares upon it, but likewise secure it from any injury that might 
arise to it from the process. 

103. The sixth and last method of copying drawings, and at 
the same time varying their proportional magnitudes, is purely 
mechanical, and is performed by an instrument constructed for 
the particular purpose, called a Pantagraph. This method is 
very convenient for copying maps and plans, and all drawings 
that contain curved or irregular outlines, but is not suited to the 
production of right lines, though the instrument may be used in 
connexion with a ruler, for forming them. 



ON COPYING DRAWINGS. 65 

104. The pantagraph is usually made of wood or brass, from 
one to two feet or more in length, and consists of four flat rulers, 
J^ig. 21, Plate /., two of them long and two short. The two 
longer are jointed at the end A by a metallic double joint, which 
admits their opening and shutting like a pair of compasses. 
Under this joint is an ivory castor, to support this end of the 
instrument. The two short rulers are fixed by pivots at E and 
H near the middle of the long rulers, and their other ends are 
joined together by a double joint at G. By the construction of 
this instrument the four rulers always form a parallelogram. 
There is a sliding box B on the long arm E, and a similar one 
on the short arm D. These boxes can be fixed at any required 
part of the rulers by their m.illed screws. Each of these boxes 
is furnished with a cylindric tube, to carry either the tracing- 
point, crayon or fulcrum. 

The fulcrum or support K, is a brass pillar or pivot, rising out 
of a leaden weight; on this the whole instrument moves when in 
use. Other rollers or castors are applied under the joints E and 
H to support the rulers and keep them parallel to the paper. 
The long and short rulers which carry the sliding boxes, are 
graduated and marked with the proportions ^, \, \, &c., to -f^, 
for reducing or enlarging drawings accordingly. The pencil 
holder F, tracer C, and fulcrum K, must in all cases be in a right 
line; so that when they are set to any number, if a string be 
stretched over them and they do not coincide with it, we may 
be sure that an error exists in the setting of them, or in the 
graduation of the instrument. 

The long tube or crayon F, which carries a black-lead pencil, 
is maintained in a vertical position by sliding in an external tube 
in which it moves easily up and down, and a strong silken thread 
ss SIS fastened to the lower part of this crayon, passes up the same 
tube, is carried through metal eyes placed over the joints E and 
A, and is finally attached to the tracing-point C. By pulling 
this string the pencil is lifted up, and prevented marking upon 
the paper whenever desired. The crayon piece slides so easily 
in its socket, that the pencil rises and falls to accommodate any 
unevenness in the surface of the copying paper; and to insure the 
due marking of the pencil, the top of the crayon piece is formed 
into a cup for holding cents or other weights, by which the pres- 
sure of the pencil upon the paper may be increased at pleasure. 

105. To use the instrument for reducing a map or other 
drawing in any of the proportions \, l, i, i, ^-CyUS marked 
on the two bars B a7id D. Suppose, for example, ^ is required. 
— Place the two sliding boxes at ^ on the bars B and D; slip the 
tube or socket of B over the brass spindle of the lead weight K; 

9 



66 ON COPYING DRAWINGS. 

place the crayon and pencil in the tube or socket of D, and insert 
the tracing-point in the socket C, and attach the silk thread of 
the pencil to it, and the instrument will be prepared for use. To 
use it, open the two long arms or rulers until they make an angle 
with each other of from 60° to 90°. Fasten the sheet of paper 
that is to receive the copy to a large flat table, in such position 
that the pencil-point may stand over the middle of the sheet; and 
place the original that is to be reduced under the tracing-point C, 
in such manner that its centre shall also be under the tracing- 
point; and now, on passing the tracing-point over all the lines in 
the original, the pencil-point will perform the same evolutions 
upon the paper, and will produce a perfect copy of the original 
of half its size. 

106. In the same manner a copy, in any other proportion, will 
be produced by setting both the sliding sockets, B and D, to the 
numbers indicating the proportions required, on the long and 
short arms, keeping the fulcrum, pencil, and tracing-point, in the 
positions before described. 

107. If the original should be so large that the instrument will 
not extend over it at one operation, two or three points must be 
marked on the original, and the same to correspond upon the 
copy. The fulcrum and copy may then be removed into such 
situations as to admit the copying of the remaining part of the 
original; first observing, that when the tracing-point is applied 
to the points marked on the original, the pencil may fall on the 
corresponding points in the copy. In this manner, by repeated 
shiftings, a pantagraph may be made to copy an original of any 
extent of dimensions. 

108. To use the instrument for enlarging a draiving in any 
of the jyrojjortions marked on the scales; suppose \. The sliding 
pieces on the arms remain as before, or must both be set to the 
same proportion required on the long and short arms, when all 
that is necessary, is to exchange the places of the pencil-point 
and tracer, viz: to place the tracing-point at D, and the pencil at 
C, and proceed as before. 

109. The pantagraph will also copy drawings of the same size; 
but in this case every part of the figure will be reversed. To use 
the instrument for this purpose, the fulcrum must be placed in 
the central socket D, while the pencil and tracer are placed in- 
differently in the two sockets, B and C, at the extreme ends of 
the long rods, taking care when using the instrument in this way 
to make the distance AB equal to AC, by shifting the slider B 
accordingly. 

110. Drawings are sometimes made from real objects without 
using the scale and compasses, or paying strict attention to the 



ON COPYING DRAWINGS. 



67 



proportional magnitude of their parts; but upon which the real 
dimensions are figured in, so that the drawing can be made over 
again by scale at a future time. These are called rough eye- 
draughts, and they are the kind of drawings recommended in the 
first chapter to be made by the young Engineer, as memoranda 
for his future guidance; and they will, in many instances, serve 
for workmen to work from. They consume very little time for 
accomplishment, compared with other drawings, and the mode 
of executing them is merely to make as correct a representation 
of the object before you as you can, without measuring it, and 
then to take its actual dimensions with care, and insert them in 
figures upon the drawing, observing that the written line of figures 
must have the same direction as that in which the dimension is 
taken. These figures are generally placed near the centre of the 
dimension taken, and the space between them and the external 
lines are filled up b}- dotted or other lines, terminating in arrow- 
heads, or angular points, which points indicate the exact spot to 
which the dimensions are taken, or extend, as in the figure under- 
neath, which may be supposed to represent two adjoining rooms 







A 
C 










<- 


- 20 ft. 6 in. - 


- 0) _ 

d 

00 
V 


-> 


<- 


12. 4. - 


- -> 



A 



32 feet 10 inches. 



in a plan. The largest of these is 20 feet 6 inches long, by S 
feet 2 inches wide; and the other 12 feet 4 inches long, by the 
same width. The figures under the diagram show that the entire 
length of the building is 32 feet 10 inches, being the sum of 20 
feet 6, and 12 feet 4. The proportion of these dimensions is not 
observed in the figure, but it will be evident that with such di- 
mensions given a correct plan to scale can at any time be pro- 
duced, or the rooms could be set out for building. 

111. This kind of drawing, with the difference only of its being 
accurately laid down to scale, is the one almost constantly resort- 
ed to by Engineers, in making their working drawings for the 
erection of machinery. They save much time, and are often 
more intelligible to the workman than drawings in greater de- 
tail. If, for instance, a bricklayer or mason were employed to 
construct the necessary building for containing a steam engine, 
or any other complicated machine, in which a strong wall or 
basement should be required for supporting the steam cylinder, 



68 OP MOULDINGS. 

all the workman would require would be the height and other 
dimensions of such wall, and the position of the centre of the 
cylinder upon it, the position and distance of the main gudgeons 
of the beam, the central'line of the fly-wheel shaft, and diameter 
of the fly-wheel, the central line of the steam boiler and steam 
pipes, &c., all which particulars can be more accurately and in- 
telligibly laid down by mere centre lines, with dimensions figured 
in upon, and between them, than by the most elaborate drawing, 
which might tend to confuse rather than to instruct, and would 
occupy much time for its formation. 

112. As a first step in the preparation or drawing of plans of 
buildings, or machines already erected, of rooms, halls, or pub- 
lic buildings, and e-7en for making plans of single fields of regular 
form, this mode of drawing is constantly resorted to. It being 
more simple and easy to make a sketch or eye-draught of what 
is before you, and afterwards to figure in the dimensions upon 
such sketch, than it is to record or register them in any other 
way. In making such drawings of fields it will, however, be ne- 
cessary either to measure one or more angles in the corners, or 
else to measure a diagonal from one corner to another; because 
the eye is apt to be deceived, and that may appear to be square, 
or to have right angles at its corners, which is, in fact, a rhom- 
boid or trapezium, difiering so slightly from a rectangular figure 
as not to be perceived. 

113. Mouldings are members introduced into constructions, 
generally, for the purpose of ornament alone, although they may 
frequently be resorted to with advantage, for increasing strength. 
They belong equally to the work of the stonemason, the joiner, 
the plasterer, and the ironfounder, and on this account a descrip- 
tion of them does not appear to belong to any class of work with 
more propriety, than to the present chapter upon drawing; be- 
cause, under this head, the mode of producing or drawing them, 
may be given. 

114. Mouldings are of great antiquity, having been introduced 
into buildings in the earliest ages. With the Egyptians they 
were very large, simple, and few in number; the Grecians in- 
creased their quantity, and made them smaller; but in Roman 
architecture they were not only multiplied in number, but much 
diminished in niagnitude. They are used round columns and 
upon flat surfaces, and are seldom introduced near the middle of 
a construction, but are placed at or near the sides or angles, or 
serve to divide one member from another. 

115. The simple mouldings of the ancients are still used in 
preference to others, and are distinguished by the names of the 
fillet, the torus, the astragal, the ovalo, the echinus, the scotia, 



OP MOULDINGS. 69 

the cavetto, the cymatium or cyma recta, and the cyma reversa. 
The modern mouldings added to these are, the quirked bead and 
the reed. All mouldings are distinguished from each other by 
the profiles or sections they present when cut across. Thus Fig. 
28 is a section of a fillet, which is nothing more than a mere rec- 
tangular projection, rising above a plane surface, and usually made 
much wider on its face, than the quantity of its projection. It is 
frequently called a band. 

The Torus is a convex moulding, the section of which is a 
semicircle, or nearly so, projecting from a flat surface. See Fig. 
29. It is usually the lowest number of the shaft of Grecian 
columns. 

The Astragal, Fig. 30, is a semicircular projection placed upon 
a fillet; the quantity of fillet shown on each side of it being gene- 
rally equal to the projection above the flat surface, on which it is 
placed. 

The Ovalo, Fig. 31, a, difiers from the two last in only exposing 
a quarter of a circle. It is generally sunk upon the solid angle 
of a piece of work, so as to put on the appearance shown at b, in 
the same figure. 

The Echinus, Fig. 32, resembles the ovalo, but its outline is 
elliptical instead of circular. It frequently occurs in the capitals 
of Grecian Doric columns, and is sometimes called the Grecian 
ovalo. 

The Scotia is among the concave mouldings, and is the reverse 
of the torus, its section presenting a concave semicircle, which is 
usually bordered by two narrovv fillets. See Fig. 33. 

The Cavetto is another concave moulding, being a quarter of a 
circle, and the reverse of the ovalo. See Fig. 34. It is occa- 
sionally made elliptical, or the reverse of the echinus. 

The Cymatium or cyma recta, is an undulated moulding, the 
upper half of which is concave, and the lower half convex. See 
Fig. 35. It is, in fact, an ovalo added below a cavetto, and is 
formed of two quarter circles, struck from the two dots, one with- 
in and the other w^ithout the moulding; their positions being 
formed by dividing the width of the moulding into two equal 
parts. 

The Cyma reversa, Fig. 36, so exactly the reverse of the last, 
being struck from two centres formed as before, but in such man- 
ner that the upper half of the moulding is convex and the lower 
half concave. This moulding is more frequently introduced into 
modern work than the last, and is generally called an OG, or 
talon, by workmen. 

The modern OG, or cyma reversa, is made to consist of two 
semicircles instead of two quadrants of circles, united in the same 



70 OP MOULDINGS. 

way; the place of the centre being formed by dividing the width 
of the moulding into four equal parts. It is thought to produce a 
bolder and more handsome appearance. See Fig. 37. The nar- 
row angular indentation marked ^, produced by this construction, 
is called a quirk. 

The modern bead is the same as the torus, except that it is ac- 
companied by a quirk on one or both sides, which occasions 
more than half the circle to become visible, as shown in Fig. 38. 

The reed is a number of cylindric projections or indentations, 
placed close and parallel to each other in longitudinal direction, 
so as to present sections like Fig. 39; and which are called con- 
vex or concave reedings. 

116. The above simple mouldings are sometimes used alone, 
but are most frequently grouped or compounded according to the 
taste of the designer, so as to produce the width and boldness or 
projection required, of which Fig. 40, may serve as an example. 
In this Fig. a is a fillet, 6 a cavetto, c a modern or quirked OG, 
d an astragal, and e a quirked bead. 

Whenever two lines of mouldings meet at a right angle, they 
are made to join, by cutting the two surfaces that come together, 
into angles of 45° each, and such a joint is always called a mitre; 
its appearance is shown aty, in Fig. 41. 

117. Compounded mouldings derive different general names 
from the positions in which they are placed. Thus the mould- 
ings round the top of a room next the ceiling, or over a row of 
columns, is called a cornice. These same, or other mouldings, 
near the bottoms of the walls of a room, or under columns, would 
constitute a surbase, or a plinth if quite at the bottom; and pan- 
nels are surfaces surrounded by mouldings. 



71 



CHAPTER III. 



ON THE PRINCIPLES OF MENSURATION. 



118. Mensuration is that branch of mathematics which shows 
the mode of computing the magnitude of objects and the quantity 
of material they contain; and as all kinds of artificers work is 
paid for according to its measurement, and the total value of any 
piece of work is compounded of the value of its materials, added 
to the cost of the work or labour for putting them together, so it 
is quite necessary that the Engineer, the Architect, the Surveyor, 
and the builder or constructor, should be acquainted with the 
modes of taking measurements; as without such knowledge it 
would be impossible to prepare an estimate or valuation of work 
antecedent to its execution, or to determine its value when com- 
pleted. 

119. Mensuration is generally divided into three distinct 
heads, called lineal or running, superficial, and solid measure. 
The first only contemplates extension in length; the second the 
quantity of surface to be examined, without any regard to its 
depth or thickness; and the latter takes in all dimensions, or 
length, breadth and thickness. For the above reason the tech- 
nical phrase applied to the second head or superficial measurement 
is called squaring dimensions^ while the latter is called cubing 
them. Lineal measurement is so simple and well understood 
that it requires no explanation; therefore superficial measurement 
will be considered in the first instance. 

120. The computation of either kind of measurement requires 
a knowledge of arithmetic for its performance; and the operations 
are conducted in two ways, according to the divisions made use 
of in the measures adopted. Thus the surface of land is measured 
by acres, roods and perches, which are estimated by a chain 
containing 100 equal links; therefore land measure is conducted 
by common decimal arithmetic. A similar mode of measurement 
is also adopted in canal and road work. But as the work of car- 
penters, joiners, and many other artificers, is measured by yards, 
feet and inches, in which the foot, as the derivative measure, is 



72 ON THE PRINCIPLES OP MENSURATION. 

divided into twelve equal parts called inches, so the operations 
upon these dimensions are usually conducted by what is called 
the duodecimal process. The name of the first being derived 
from the Latin word decern, ten, and the latter from duodecem, 
twelve. All the operations may, however, be conducted by 
decimal arithmetic, notwithstanding that custom has introduced 
the duodecimal method into use for some kinds of work, and it 
must therefore be used. 

121. Common arithmetic is so generally known, that it is 
needless to say anything about it, presuming that its operations 
are known to all. Duodecimal arithmetic, on the contrary, though 
generally taught at schools, is frequently forgotten, on account^ 
of its never being used or practised except by those who are 
concerned in building operations, where it is of every-day occur- 
rence. It may therefore be useful to make a few observations 
upon it. 

122. Addition, subtraction and division, are performed by the 
ordinary rules of compound addition, subtraction and division; 
all that is necessary being to recollect that instead of carrying 
tens to the next column or the left, or borrowing tens from it, 
that the amount carried or borrowed will depend upon the value 
of the units we are working upon, as in the following example 
of the addition of two quantities of brickwork. 

» Add 7 rods 3 qrts. 12 feet and 7 inches 

to 12 2 74 - 9 



Answer 20 2 4 4 

To understand this, it is necessary to premise that brickwork 
is always measured or estimated in square rods, quarters of rods, 
feet and inches. The rod consists of 272 superficial feet, conse- 
quently its half will be 136 feet, and its quarter 83 feet. Now, 
in working the above addition, the sum of 7 and 9 inches amounts 
to 16 inches, which is 1 foot and 4 inches, therefore the 4 inches 
are set down, and the one foot is carried to the next column of 
feet, in which we find 12 feet and 74 feet amount to 86, and one 
carried makes 87 feet; but as 83 feet make a quarter rod, the 83 
must be subtracted from 87, leaving 4 feet to set down, and one 
quarter of a rod to carry to the next column, which, being added 
to the 3 and 2 quarters found there, makes 6 quarters. But 6 
quarters are equal to one whole rod and two quarters, so that the 
2 only are put down, and the one rod is carried to the 7 and 12 
rods of the next column, making the whole sum 20 rods, 2 quar- 
ters, 4 feet, 4 inches. 

123. Suppose it is required to subtract 4 lineal yards, 2 feet 



ON THE PRINCIPLES OF MENSURATION. 73 

and 3 inches from 50 yards, 1 foot and 2 inches, then the opera- 
tion will stand thus: 

50 1 2 
4 2 3 



45 1 11 

3 inches cannot be taken from 2 inches, therefore the 1 
foot must be borrowed from the next column; but as feet and 
inches cannot be assimilated, that foot must be expanded to its 
actual value in the computation, and that being lineal measure, 
will be 12 inches, so that in fact we borrow 12 inches to add to 
the 2, making 14 inches; from w^hich, subtracting 3, the remain- 
ing 11 inches must be set down. Next we have to subtract 2 
feet from 1 foot. But the one foot has previously disappeared — 
having been lent to the inches; therefore, to continue the operation, 
one yard, equal to 3 feet, must be borrowed from the 50 yards; 
and now the subtraction becomes converted into 2 feet from 3 
feet, and one remains, which is put down. Next we have 4 feet 
to take from 50 feet. But the 50 feet has been diminished to 49 
by having lent one to the inches, so that in fact we have to take 
4 feet from 49, and 45 feet remain and are set down. 

This is exactly reversing the operation of subtraction, as gene- 
rally taught; because, instead of considering each group of num- 
bers in the upper line as diminished by borrowing, they are per- 
mitted to retain their first value, and the sums borrowed are added 
to the figures in the lower line without any apparent reason; and 
the above explanation is introduced merely to show the philosophy 
or principle of the operation. To prove how necessary it is to 
pay due regard to the values of the units we are operating upon, 
the example above given is repeated with the same figures, but 
on a presumption that they now represent square instead of lineal 
quantities, which will alter the result, although the mode of 
working remains the same. 

Subtract 4 square yards, 2 square feet, and 3 square inches 
from 50 square yards, 1 square foot, and 2 square inches. 

50 1 2 
4 2 3 



45 7 143 
In this case the 1 foot borrowed from the inches is equal to 144 
square inches, which, added to the 2, makes 146, and 3 subtracted 
from that, leaves 143 square inches. The yard borrowed for the 
feet is equal to 9 feet, therefore the subtraction is 9 — 2=7, 
while the yards remain the same as in the former case. 

124. The same observance of values must be preserved in car- 
lo 



74 ON THE PRINCIPLES OF MENSUKATION. 

rying on the operations of division; but in general they are more 
simple than the others, since it frequently happens that this rule 
is applied to obtain the value of one unit of work out of a great 
number that have been executed. Thus, from knowing the cost 
of any number of yards of work, we may deduce the value of 
one yard; or knowing how many bricks have been used in a given 
number of rods of work, we may ascertain how many are re- 
quired for one rod. 

125. This rule may evidently be worked in two ways, viz: 
by reducing all the larger denominations of quantity, either to 
their smallest denominations, or to a denomination equal to that 
of the divisor, and proceeding as in common division; or the 
largest denomination may be divided first and its quotient set 
down. If there is a remainder, that must be reduced to the de- 
nomination next lower in value to which it is added, and the 
division proceeds as before; and this operation is to be repeated 
until carried to the smallest denomination we may want. 

126. The next and most important rule to the Engineer and 
builder is multiplication of duodecimals, or, as it is very fre- 
quently called, cross multiplication, on account of the nature of 
the process by which the operation is conducted. By workmen 
it is generally called squaring dimensions. It applies only to 
dimensions that are taken in feet, inches, and parts of an inch. 

Rule. — Multiply each term in the multiplicand from the right 
hand by the feet only in the multiplier, and write each result 
under its respective term; observing to carry one unit of the next 
highest denomination of value for every twelve of the one below 
it. That done, proceed in like manner to multiply each term of 
the multiplicand by the inches only of the multiplier, and set the 
results of each term under the first obtained product; put each term 
one place to the right hand of those obtained by the first multiplica- 
tion. The addition of these two lines will be the answer required. 

Example. — Multiply 59 feet 6 inches by 3 feet 11 inches. 

59 6 
3 11 



178 6 
54 5 6 

233 6 
In the result, the left hand parcel of figures are feet; the next 
to the right hand, inches; but as none occur in this example, the 
place of inches is held by a 0. The right hand column is twelfths 
of an inch, of which 6 occur, equal to half an inch. The prac- 
tical rule is, that whenever the parts of an inch amount to 6 or 



ON THE PRINCIPLES OP MENSURATION. 



75 



more, it is written down an inch; while if such parts amount to 
less than 6, they are discarded. The above number would con- 
sequently be written 233 feet 1 inch. The third column of 
figures is thus dispensed with; and when this giving and taking 
principle is applied to a great number of dimensions, the result 
is found to come near enough to truth for all practical purposes. 
127. Whenever the number of inches that occur are aliquot 
parts of a foot, the process ma)'- be shortened by using the rule 
of practice. Thus, suppose we have 

6 feet 4 inches to 
multiply by 12 6 



76 
3 




2 



79 2 

The multiplication of the upper line by 12 feet produces ex- 
actly 76 feet; and then, as 6 inches is half a foot, there is no ne- 
cessity to go through the second multiplication, but we may take 
half the multiplicand, or 3 feet 2 inches, and setting this under 
the 76, the sum will give the amount sought, or 79 feet 2 inches. 

In like manner, suppose we had to 

multiply 33 feet 9 inches 
by 10 4 



337 
11 



6 
3 



348 9 

The multiplication of 33 feet 9 inches by 10 feet, gives 337 
feet 6 inches; and as 4 inches, the next multiplier, is one-third of 
a foot, we have only to take the third part of 33 feet 9 inches, 
or 11 feet 3 inches, and adding this to the product of the first 
multiplication, will give 348 feet 9 inches, the sum required. 

128. To avail of this rule, it is only necessary to commit to 
memory the following practice table of feet and inches: 

1 inch is y^^th of a foot. 
1 J inches is |^th 



2 ? 


hth 


3 , 


ith 


4 , 


Id 


6 , 


? i 


8 , 


, Ids 


9 J 


#ths 



76 



ON THE PRINCIPLES OF MENSURATION. 



129. In England, where 12 pence make a shilling, (one of the 
commonest coins of currency,) every school-boy is required to 
learn his pence table by heart; and as 12 inches make a foot, as 
well as 12 pence a shilling, the acquirement of this table affords 
surprising facility in working duodecimals and casting up all 
artificers' work. It is therefore strongly recommended that the 
student should commit the following table to memory. It is the 
common English pence table, altered by substituting the words 
feet and inches for shillings and pence. 



Table 


of Inches 


in Feet. 








Feet. 


Inches. 






Feet. 


Inches. 


12 inches make 1 






70 




5 


10 


18 ,, 1 


6 




SO 




6 


8 


24 ,, 2 






90 




7 


6 


30 „ 2 


6 




100 




8 


4 


36 ,, 3 






110 




9 


2 


40 „ 3 


4 




120 




10 




42 ,, 3 


6 




130 




10 


10 


48 „ 4 







140 




11 


8 


50 „ 4 


2 




144 




12 





60 ,, 5 






150 




12 


6 



130. Those who enter into the employment of an Engineer's, 
Architect's or Surveyor's office, will have ample means of mak- 
ing themselves perfect in this kind of computation, because the 
usual arrangement is for the senior clerks (who on account of 
their experience and knowledge may be trusted with this duty) 
to go out and take dimensions of work that has been executed; 
and they bring their books, when filled with dimensions, to the 
junior clerks in the office, to square and abstract the same, in a 
manner that will be hereafter described. The junior clerks are 
frequently kept for months together at this daily occupation; and 
such is the facility acquired by this constant practice, that in 
many cases it is not necessary to go through the process of mul- 
tiplication, for the result becomes evident upon inspection, and 
may be put down at once without any arithmetical operation. 
On this point the author speaks from his own experience. 

131. For the same reason that some notice has been taken of 
duodecimal arithmetic, it may be servicable to make a few short 
observations on fractions; because, as these are not very exten- 
sivel)^ used in the ordinary occupations of life, the rules for treat- 
ing them are often forgotten, while their use is absolutely neces- 
sary in many investigations of science. No attempt will be made 
to explain the foundations of these rules, but merely to revive a 
recollection of their existence. 



ON THE PRINCIPLES OF MENSURATION. 77 

132. A unit expresses one single object of computation in pure 
mathematics, without any reference to what that object may be. 
It is simply one. But in mixed or palpable mathematics some 
idea of existence is always attached to it, as a pound, an ounce, 
a penny, a foot, &c., and sums arise from the multiplication of 
units. 

133. So long as a unit remains whole and entire it is called 
an integer, or integral, or whole number. It is, however, fre- 
quently necessary to examine a less quantity than one whole or 
entire thing; and in that case we have to consider the unit as 
broken or divided, and the parts into which it is so broken are 
called fractions of that unit. Common or vulgar fractions are 
marked by two figures, ane above the other, having a line drawn 
between them, thus, i, -§-, |, -f^, -//q-, &c. The lowest figure, or 
that under the line, indicates into how many equal parts the in- 
teger has been broken or divided, and thus gives denomination 
to the fraction, and is therefore called the denominator; while 
the upper figure states the number of the parts or divisions that 
are to be taken into account, and is therefore called the nume- 
rator. 

134. From the above short account it will be evident that, 
although a given quantity can only be expressed by one set or 
form of integral numbers, it may be stated in an almost infinite 
variety of forms by vulgar fractions, and that all those above 
stated express the same quantity; for if we divide a thing into 
2 parts and take 1 of them, or into 6 parts and take 3 of them, 
or into 8 and take 4, or into 100 and take 50, &c. &c., we 
shall in every case have the same quantity, which will be one 
half of the first quantity. One half is therefore called the lowest 
denomination of all the above set of fractions; and one of the 
most common operations that occurs is the alteration of fractions 
from one form of expression into another, without altering their 
real value, in order to suit them for the operations of addition, 
subtraction, &c. From the nature of fractions, if both terms are 
increased or diminished in an equal degree, the value of the frac- 
tion will remain unchanged; multiplication will increase the 
number of figures and make the expression more complicated, 
while division will reduce and render it more simple; and the 
largest number that can be employed to divide both terms, with- 
out a remainder, will of course reduce a fraction to its smallest 
and most simple expression. 

135. The first object consequently in treating fractions is. 

To find the greatest common measure of two or more nutnhers . 
Rule. — If there are two numbers only, divide the greater by 



78 ON THE PEINCIPLES OP MENSURATION. 

the less. Then divide the divisor by the remainder; and so on, 
always dividing the last divisor by the last remainder, till no- 
thing remains; and the last divisor of all will be the greatest 
common measure. 

136. When there are more than two numbers, find the great- 
est common measure of two of them, as before; then do the same 
for that common measure and another of the numbers; and so 
on through all the numbers; and the greatest common measure 
last found, will be the answer. 

If it happen that the common measure thus found is 1, then 
the numbers are said to be incommensurable, or have no common 
measure. 

Example. — To find the greatest com«ion measure of the num- 
bers 1908, 936, and 630. 

936)1908(2 
1872 



36)936(26 Hence 36)630(17 

72 36 



216 270 

216 252 



18)36(2 
36 



Hence 36 is the greatest common measure of the two first 
numbers 1908 and 936; and 18 is the common measure of those 
two numbers and 630. 

137. To reduce a vulgar fraction to its lowest denomination , 

or simplest expression. 

Rule. — Divide the numerator and denominator of the given 
fraction by that number which is their greatest common measure, 
(found by the last rule,) and the two quotients disposed over each 
other, in the former order of the figures, will be the simple frac- 
tion sought. 

Example. — What is the lowest denomination of ^^g-? 

The first part of the operation, shown in the last example, would 
be necessary upon these numbers, if it had not previously in- 
formed us that 36 is their greatest common measure. That 
known, it is only necessary to divide 936 and 1908 by 36; and 
the two quotients obtained will be 36 and 53, which, formed into 



ON THE PRINCIPJLES OP MENSURATION. 79 

a fraction, will be |f ; and this is the lowest expression of this 
fraction, because 53 is not divisible by any number that will di- 
vide 36 without a remainder. 

Note. — Any number ending with an even number, or a cipher, 
is divisible, or can be divided by 2. 

Any number ending with 5 or 0, is divisible by 5. 

If the two right hand figures of any number are divisible by 4, 
the whole number may be divided by 4. 

If the three right hand figures of a number are divisible by 8, 
the whole number may be divided by 8. 

If the sum of the figures constituting any number is divisible 
by 3 or 9, the whole number is divisible by 3 or 9. 

If the right hand number be even, and the sum of all the num- 
bers be divisible by 6, the whole number will be divisible by 6. 

138. To reduce several fractions to a common denominator. 

Rule. — Multiply each numerator of the several fractions into 
the several denominators, except its own denominator; and mul- 
tiply the whole of the denominators into each other. The pro- 
ducts of the first will be the several new numerators; and the 
product of the last the common denominator. 

Example. — Reduce ^oj f ? t? ^^^ f to a common denominator. 

For the numerators, 6x4x7x6 = 1008; 2x10x7x6 = 840; 

1X10X4X6 = 240; and 3x10x4x7 = 840. 

For the common denominator, 10X4x7x6 = 1680. 

Hpnre -^- = i?-^-^- 2_ — _8_4p_. \ — 24o . j,„j 3 — _8j_o_ ^ni Up 

XXeui^C JO 16 8 > 4 16 8 0) 7 1680? '*"'-' "6" 16 8 OJ ^ ^^^ "*= 

the reduction of the several fractions required. 

139. Fractional notation is not only capable of expressing 
broken parts of a unit or integral number or quantity, but quan- 
tities greater than unity; because the numerator may be, and fre- 
quently is, greater than the denominator without at all affecting 
the nature of the fraction; thus the fractions ff or |^, are each of 
them equal to two integers. To distinguish these and other frac- 
tions from each other, the following designations have been given 
to them. 

Proper fractions are all such as have their numerators smaller 
than their denominators; as -J, f, &c. 

Improper fractions are such as have their numerators equal 
to, or greater, than their denominators; as |, f, |, &c. 

Compound fractions are fractions of fractions, which are dis- 
tinguished by having the word <^of,^' introduced into their ex- 
pression; as i off, or \ of yV? and \ of yV- 

Mixed fractions, or mixed numbers, are such as consist of a 
whole number combined with a fraction; as 8|, 12f, and 17|i. 



80 ON THE PRINCIPLES OF MENSURATION. 

140. To reduce a mixed number to an improper fraction. 

Rule. — Multiply the integer, or whole number, by the de- 
nominator of the fraction, and add the numerator of the fraction 
to it; when the amount will be the new numerator to be placed 
over the former denominator. 

Example. — Required the improper fraction of ISS^^? 
183X21 + 5=3848: or lii-« 

' 2 1 

141. To reduce an improper fraction to its proper terms. 

Rule. — Divide the numerator by the denominator, and the 
quotient will be the answer. 

Example. — Required the proper terms for il±l? 

3848-7-21 = 183/1. 

142. To reduce a compound fraction to a single fraction. 

Rule. — Multiply the whole of the numerators into each other 
for a new numerator, and the whole of the denominators into 
each other for a new denominator. Set this down as a single 
fraction; and, if required, reduce it to its lowest denomination, 
(by par. 137.) 

Example. — Reduce f of |- of -/o^, to a single fraction. 

For the new numerator 3X5x9= 135 



For the new denominator 4X6X10= 240 



and if this fraction 



is reduced to its lowest denomination, it will become y 



9 



6 



143. To reduce a fraction of one denomination to a fraction 
of a higher denomination^ retaining the same value. 

Rule. — Reduce the given fraction to a compound fraction by 
comparing it with the denominations through which it has to 
pass, and then proceed as with com.pound fractions. 

Example. — Reduce ^ of a lb., avoirdupois, to the fraction of 
a hundred weight of 112 lbs. 

^ of yi^ lbs. = ^ ^ ^ ^ ^ ^ ^g^ ^ = tI^ or reduced yb of 1 c wt. 

144. To reduce a fraction from one denomination to another 
retaining the same value, when the numerator of the new 
fraction is given. 

Rule. — Multiply the denominator of the fraction by the given 
numerator, and divide the product by the numerator of the frac- 
tion. 

Example. — Reduce f to a fraction of the same value, whose 
numerator shall be 9. 



ON THE PKINCIPJLES OF MENSURATION. 81 

4x9-i-3=12; hence 3% ^i^l ^^ the new fraction; for as 3 : 4 
::9:12. 

145. To reduce a fraction from one denomination to another 
of the same value, when the denominator of the new fraction 
is given. 

Rule. — Multiply the numerator of the fraction by the given 
denominator, and divide by the denominator of the fraction. 

Example. — Reduce f to a fraction of the same value, whose 
denominator shall be 24. 

3X24-^4=18j hence ~| is the fraction sought; for as 3 : 4 : : 
18 :24. 

146. To reduce a mixed fraction to a simple fraction. 

Rule. — Multiply, separately, the numerator and denominator 
by the denominator of the fraction in the mixed quantity; add 
the numerator of the fraction to where it belongs, and reduce the 
fraction to its lowest terms by (137.) 

Example 1. — Reduce -— ^ to a simple fraction. 

234- C23X7 + 5 = 166 ,., , J . 83 



t=\ 



38 ?3SX7 =266 



which reduced is 



00 



47 
Example 2. — Reduce -— - to a a simple fraction. 

65f ^ 

4r C47X5 z=2S5 , . , , , . , 

^— r= -Sn^ ^ \ A -—-r which reduced is 4- 
^0^ ^65x5+4 = 329 ^ 

147. To reduce a fraction to its proper or nominal value. 

Rule. — Multiply the numerator by the common parts of the 
integer, and divide by the denominator. 

Example. — Reduce J- of 1 lb. troy to its proper denominations 
of ounces, pennyweights, and grains. 

1^3X12 ozs.=:36 ozs.-^-5=7|ozs. ; ioz.=lx20 dwts. -7-5= 
4 dwts. 

So that I of 1 lb. troy, is equal to 7 ozs. and 4 dwts. 

148. To reduce the nominal value to the fraction of an integer. 

Rule. — Reduce the nominal value to its lowest term, for the 
numerator of the fraction; and the number of units in the integer 
will be the denominator. Reduce the fraction, if necessary, to 
its lowest terms. 

Example. — Reduce 2 roods and 20 poles to the fraction of an 
acre. 

2 roodsX40 poles+20 poles=100 

1 .yA J ^^/^ 1 ttt; or if reduced |. 

1 acreX4 roods X40 poles =160 ^ 

11 



82 ON THE PRINCIPLES OF MENSURATION. 

ADDITION AND SUBTRACTION OF VULGAR FRACTIONS. 

149. Before fractions are reduced to a common denominator 
they are quite dissimilar, as much so as dollars and cents are; 
and, therefore, cannot be incorporated with one another any more 
than these can. But when they are reduced to a common de- 
nominator, and made parts of the same thing, their sum or differ- 
ence may then be as properly expressed, by the sum or differ- 
ence of the numerators, as the sum or difference of any two quan- 
tities whatever. The first step, therefore, towards the addition 
or subtraction of fractions, is to reduce them to a common de- 
nominator. This done, for addition, we have the following 

Rule — add all the numerators together and place their sum 
over the common denominator. 

Note. — All compound fractions must be reduced to simple 
ones; fractions of different denominations to those of the same 
denomination; and mixed numbers must either be reduced to im- 
proper fractions, and be so added with the others, or else the frac- 
tional parts only added, leaving the integers to be united after- 
wards. 

150. FOR SUBTRACTION. 

The fractions being prepared as for addition, subtract the one 
numerator from the other, and set the remainder over the com- 
mon denominator, for the difference of the fractions sought. 

151. MULTIPLICATION OF VULGAR FRACTIONS. 

Rule. — When the given numbers require it, prepare them by 
any of the foregoing rules; then multiply the numerators into 
each other, for a new numerator; and the denominators into each 
other for a new denominator. 

Note. — A fraction is best multiplied by an integer, by dividing 
the denominator by it; but if it will not exactly divide, then mul- 
tiply the numerator by it. 

152. DIVISION OF VULGAR FRACTIONS. 

Rule. — Having prepared the fractions as for multiplication, 
divide the numerator of the one fraction by the numerator of the 
other, and the denominators in like manner, if they will exactly 
divide; if not, multiply the numerator of the one by the denomi- 
nator of the other, reciprocally, to obtain the required fraction. 

Example of 1st case. — Divide 14 by 2 now 14-f-2=7 , 

-^ t; 1 « « - ^-he Ans. 
27 3 and 27^3=9 

2nd case, 14 by 2 here 14x3=42^ which reduced to its lowest 
27 3 27X2=54 3 denomination is, also, |^. 



ON THE PRINCIPLES OF MENSURATION. 83 

Note. — A fraction is best divided by an integer, by dividing 
the numerator by it; but if it will not exactly divide, then multi- 
ply the denominator by it. 

153. RULE OF THREE IN VULGAR FRACTIONS. 

State the question as in the rule of three of whole numbers; re- 
duce the fractions that require it as in the other rules: invert the 
first term in the proposition by changing the places of the nume- 
rator and denominator; then multiply the three terms continually 
together, and the product will be the ansvver. 

Example. — Iff of a yard of paving cost f of 4 dollars, what 
will ^ of a yard come to? 

Iff cost f what will yV cost? 

Inverting the first term makes this | :|-:: f^x and multiplying 

the terms will give 

4X5X 9=180 18 3 

^ or — or _ ,=,2, dolls. 

3X8X10=240 24 4 

The effect of inverting the first term is that the second and 
third terms are multiplied together, and divided by the first term, 
as in the rule of three in whole numbers. 

154. DECIMAL FRACTIONS. 

Vulgar fractions arise naturally out of the transactions of com- 
merce; but there is so much trouble and loss of time attendant on 
their necessary reduction and computation, that they are seldom 
admitted or made use of in the arithmetical operations of science; 
but another species of fraction is generally adopted, in which the 
denominator is fixed, being always 1, with as many ciphers 
placed after it as the numerator has figures. This mode of no- 
tation has many advantages, one of the most obvious of which is, 
that as the denominator is known, there is no occasion to write 
it down or introduce it below a line, as in vulgar fractions, but 
the fraction is expressed by merely setting down the numerator 
after a point or full stop, which separates it from the integral 
number in the case of a mixed number, or indicates that it is a 
fraction if it stands alone; though, in some cases, a cipher is in- 
troduced to the left of the point to avoid mistakes, and indicate 
the existence of the fraction more unequivocally. Thus y^ ex- 
pressed in decimal fractions would be, .4 or 0.4; and -y/q- oi* two 
would be written, .24 or 0.24 and 0.074. So, in like manner, 
the mixed number 3yoV would be written, 3.25. 

155. Ciphers placed on the right hand of decimals make no 
alteration in their value, for .5, or .50, or 0.500 have all the same 
value, though differently expressed. These numbers would be 



84 ON THE PRINCIPLES OF MENSURATION. 

read 5 tenths, 50 hundredths, and 500 thousandths, which, after 
what has been said on fractions, will evidently be equal to one 
half. A cipher placed on the left of a decimal will, however, 
alter its value, because decimals increase in their denomination 
from left to right, or in an order exactly the reverse of whole 
numbers; consequently, if the above numbers were written .05, 
.005, &c. the first would indicate 5 hundredths, and the next 5 
thousandths; because, as before observed, the denominator that 
has to be mentally supplied is constantly 1, with as many ciphers 
after it as there are digits in the numerator; and left hand ciphers 
reckon as digits. 

156. The only disadvantage of decimal fractions is, that quan- 
tities very frequently occur that are not an aliquot part of 10, or 
commensurable by decimal notation; and in such cases the exact 
quantity cannot be expressed by adecimal fraction, and we must 
be satisfied with an approximation to it; but that approximation 
may be brought so close as to become an almost perfect expres- 
sion. In vulgar fractions we may conceive the integer to be 
broken into just as many parts as are necessary to obtain a deno- 
minator that shall express the exact quantity; but in decimal 
fractions, where the denominator is fixed, this advantage is lost. 
All the quantities that can be perfectly represented by decimal 
fractions are tenths, hundredths, thousandths, &c. of a quantity, 
or its quarter, half, or three-quarters, which are written 0.1, 0.2, 
0.3, &c. for tenths; 0.25 for a quarter; 0.50 for half; and 0.75 for 
three-quarters; because 25, 50 and 75; are the exact quarter, half, 
and three-quarters of a hundred. But all other quantities which 
do not admit of exact division must be expressed approximately 
by decimals. Thus, if we desire to express the third of a thing, 
it will be found that it cannot be done exactly, because neither 
10 nor any multiple of 10 has an exact third, 10 not being divi- 
sible by 3 without a fractional remamder. To express a third 
we must therefore write 0.3, and multiplying this fraction by 3 
to convert it into an integer, we shall have but nine-tenths; so 
that one-tenth of the whole quantity is lost by this mode of nota- 
tion. In order to obviate this inconvenience as far as possible, 
decimals of higher quality must be used. Thus, instead of sup- 
posing the integer to be divided into 10 parts, we divide it into 
100, we should then have to write 0.33 instead of 0.3; and by 
taking 33 hundredths instead of 3 tenths, we shall only lose one 
hundredth of the quantity. Again, if the integer is divided into 
1000 parts, then its third would be written 0.333, or three hun- 
dred and thirty-three thousandths, and the ultimate loss would 
be reduced to one thousandth. By using seven figures in the 
decimal, the loss would be reduced to one millionth, and so on. 



ON THE PRINCIPLES OF MENSURATION. 85 

This explains what is meant by expressing decimal fractions to 
a certain number of figures, or, as it is sometimes called, to so 
many places of figures, because in all numbers not decimally 
commensurable, approximation to precision can only be obtained 
by increasing the places of figures; while, on the contrary, such 
as are exact multiples may be as correctly represented by 1, 2 
or 3 figures, as by the greatest multiplication of them. No ad- 
dition of figures can improve the expression of one half by 0.5, 
because it is perfect; but a quarter cannot be represented by one 
decimal, because 10 has no quarter without a fraction, but 0.25 
is a correct expression for it, 25 being the exact quarter of 100. 

157. The left hand figure of a decimal, or that immediately 
following the point, is called the 1st place, or place of primes, 
and always expresses tenths; the next figure to the right is called 
the 2nd place, or place of seconds or hundredths; the next, the 
3d place, expressing thousandths, each figure to the right having 
a denomination 10 times larger than that to its left, and conse- 
quently expressing a quantity 10 times smaller than the one that 
preceded it. 

158. All such decimals as express exact quantities by a certain 
number of figures and are complete, are called finite, as 0.125, 
which is an exact eighth. This also is the case with decimals that 
accord accurately with vulgar fractions, as well as with whole num- 
bers. Thus 0. 958 is an exact and complete representation of -|-|^. 

159. When decimals can never be made to accord exactly with 
given numbers, although their places of figures should be infinitely 
continued, they are called infinite decimals. One-third, or two- 
thirds of a quantity, are instances of this kind, for they can only 
be expressed by 0.3333 or 0.6666, which numbers would, if con- 
tinued, proceed constantly without change, and yet could never 
produce an exact finite termination. 

160. When the same figures thus occur over and over again 
without change, or when a certain class of various figures occur 
and are repeated in the same order without end, the decimal is 
called a repeating or circulating one, of which 3- is an example 
among many others, for it is expressed by 0.42857142857142, 
&c , which, as written, is a decimal of 14 places of figures. In 
order to show that a repeating decimal is not complete, and to 
save the writing down of a great number of figures, it is customary 
to place a dot over the repeating figures; thus 0.3 would express 
the same as if the figure 3 had been repeated an}^ number of 
times, and is better, because there is no positive limitation to the 
repetition. Notwithstanding these imperfections of decimals, 
yet the method of using them is so simple and expeditious, that 
they are constantly resorted to for all the numerical operations 



86 ON THE PRINCIPLES OF MENSURATION. 

of science, and vulgar fractions are constantly changed into deci- 
mal ones on this account. 

IGl. To convert a vulgar fraction into a decimal fraction . 

Rule. — Add as many ciphers to the numerator of the fraction 
as may be necessary for the accuracy or number of places of the 
decimal fraction to be produced, and divide by the denominator 
of the fraction. 

Example 1. — Convert \ into a decimal fraction. 
4)300(.75, the decimal fraction required. 
28 



20 
Example 2. — Convert -^ into a decimal. 

1.000000-^99=0.01oioi, answer. 
Example 3. — Convert ~j into a decimal fraction. 

1.00000^75=0.01333, answer. 

The dots over the last two examples show that the decimals 
are of the repeating and circulating character, and therefore do 
not give finite results. 

162. To convert a deciinal into a vulgar fraction. 

Rule. — Under the figures of the given decimal write its pro- 
per decimal denominator, so as to alter it into the form of a 
vulgar fraction, and reduce it to its lowest terms by (137). 

Example. — Required, the vulgar fractions that are equivalent 
to the decimals 0.5, 0.25, 0.625, and ^.S^%S. 

.5 1 .^2S . 



10 ^ 1000 ^ 

.25 1 ,^^2S_ 9 



100 ^ 10000 '" 

163. ADDITION OF DECIMALS. 

Rule. — Treat the fractions as whole numbers^ taking care 
to place the decimal points directly under each other. Observe 
the same with all the places of figures, placing the primes 
under the primes, the seconds under the seconds, Sf^c; carry the 
tens from right to left^ and those that remain after the addi- 
tion of the fraction must be placed to the left of the point to 
represent whole numbers. 

Example. — Add together the numbers 2.25, 0.64, 0.012, and 
1.785. 



ON THE PRINCIPLES OF MENSURATION. 87 

2.25 

0.64 

0.012 

1.785 



4.687 answer. 

164. SUBTRACTION OF DECIMALS. 

Rule. — Jirrange the numbers under each other, with the 
points in a direct line, as in addition, and subtract the less 
from the greater as in common numbers. 

C2.73 
Example. — Subtract 1.9185 from 2.73 ^1.9185 

(.0.8115 answer, 

165. MULTIPLICATION OF DECIMALS. 

Rule. — Jirrange the multiplier under the multiplicand, as 
in lohole numbers, and multiply them together. From the 
product, reckoning from right to left, point off as many figures 
for decimals as there are decimals in the multiplicand and 
m,ultiplier together; but if there are not so many figures in 
the product, prefix ciphers to make up the deficiency. 

ExAiMPLE 1.— Multiply 54.368 by 4.5864. 

Answer, 249.3533952. 

Here seven figures occur in the decimals of the two factors, 
consequently the 7 right hand figures of the product are pointed 
off for its decimals. 

Example 2.— Multiply 0.003876 by 0.048624. 

Answer, 0.000188466624. 

Here both the factors are fractions, and together contain only 
9 numbers capable of multiplication; but as there are 12 digits in 
the two decimals, including the ciphers, so 12 decimals must be 
cut off from the right hand of the product; and to accomplish 
this, three ciphers are prefixed to the numbers constituting the 
product. 

166. DIVISION OF DECIMALS. 

Rule. — Divide as with whole numbers; and to know how 
many decimals to point off in the quotient, subtract the num- 
ber of digits that are in the decimal of the divisor from the 
number of digits in the decimal of the dividend, including any 
cip)hers that may have been added to complete the division, and 
the difference will be the number of figures that (counting 
from the right to the left J must be pointed off in the quotient. 



88 ON THE PRINCIPLES OF MENSURATION. 

Those numhers on the left of the decimal point are whole num- 
bers, and the rest are decimals. 

Example 1. — Divide 3424.6056 by 43.6. 

In this case the dividend contains 4 decimals, and the divisor 
1; their difference consequently is 3, which indicates the number 
of right hand figures to be cut off, viz: 

34246056-^436=78.546, answ^er. 

Example 2. — Divide 4195.68 by 100. 

419568-^100=41.9568, answer. 

In this case there are two decimals in the dividend and none 
in the divisor, therefore it might appear that only two decimals 
should be pointed off in the quotient. But in conducting the 
division it will be found that two ciphers are necessarily added 
to the decimal of the dividend in order to complete the division. 
The number 4195.68 is consequently virtually altered into 
4195.6800, which does not alter its value, (155,) but it introduces 
two more digits into the decimal, making the total number 4; 
and as there are no decimals in the divisor to deduct from this 
number, it stands good for the number of decimals to be cut off 
in the quotient as above stated. 

Note. — If the division is decimal — that is, if the divisor be 1 
with ciphers, as 10, 100, or 100, &c. — then the quotient will be 
found by merely moving the decimal point in the dividend so 
many places further to the left as the divisor contains ciphers; 
prefixing ciphers, should they be necessary. 

Examples. — 217.3^100=2.173 I 419^10=41.9 

5.16-^100=0.0516 I 0.21-M000=0.00021. 

There are several other operations to be performed upon frac- 
tions, both of the vulgar and decimal kind, but the foregoing 
have been selected as being those of most common occurrence 
and most useful to the Engineer, and they are introduced here 
to save the trouble of reference to other books, in case of the 
rules being forgotten. Those who are desirous of more extended 
information on the subject must have recourse to works upon the 
principles of arithmetic. 

167. Before arithmetic can be applied to the practical opera- 
tions of mensuration, it is necessary that the student should be 
acquainted with the geometric principles of obtaining the areas 
of surfaces; and accordingly the following problems will explain 
the rules that apply to such forms as are most likely to present 
themselves to the engineer, architect, builder, and land surveyor. 
To work the whole of them, lineal measure must be resorted to 
in the first instance, because the length and breadth or other as- 
signed measurements of an object must be taken before it is pos- 



ON THE PRINCIPLES OF MENSURATION. 89 

sible to obtain either its superficial or solid measure. These 
primitive measurements may be taken with any convenient stand- 
ard of measure, such as inches, feet, yards, &c,, but in practice 
it has become usual to apply particular standards of measure to 
particular kinds of work, as will be explained in the sequel. 

Problem XXV. 

168. To find the circumference of a circle when the diameter is 
known; or the diameter when the circumference is given. 

Rule. — Multiply the diameter by 3.1416, and the product 
will be the circumference. Or divide the circumference by 3.1416, 
and the quotient will be the diameter. 

Note. — The mixed number 3.1416 has an infinite decimal, 
consequently the operation is not quite perfect; and in very large 
circles, where great precision is required and more places of 
figures are necessary, the following, or such part of it as desired, 
may be used; 

3.141592653589793238462643383279502884197169399375, &c. 

This number is, however, introduced more as an example of 
the immense length to which an infinite decimal is sometimes 
carried, than for its utility. The proportion between the diameter 
and circumference of the circle has been calculated to 127 places 
of decimals. 

When an approximation only is required, the problem may be 
solved more rapidly by the rule of three, because diameter is to 
circumference nearly as - - - 1 to 3. 
Or more nearly as - - 7 to 22. 
Or still more nearly as - 113 to 355. 

This last proportion is very much used on account of its being 
sufficiently accurate for most practical purposes, and being very 
easily remembered, for it is a repetition of the first odd numbers 
1, 3, and 5, separated into two parcels of three numbers each. 

Problem XXVI.— i^z^. 42, Flate II. 

169. To find the length of any arc of a circle, if its chord or 

radius and angular extent are given. 

Rule for the chord. — From 8 times the chord of half the 
arc subtract the chord of the whole arc, and one-third of the re- 
mainder will be the length of the arc nearly. 

Example. — Required the length of an arc, the chord ah oi 
the whole arc being 4.65874, and the chord a c oi the half arc 
2.34947. 

12 



90 ON THE PRINCIPLES OF MENSURATION. 

14 1 ^^702 

2.34947x8=18.79576—4.65874=14.13702; =4.71234 

3 

answer. 

Rule for the radius and angle. — As 180 is to the number 
of degrees in the arc, so is 3.1416 times the radius, to the length 
of the arc. Or, as 3 is to the number of degrees in the arc, so is 
0.05236 times the radius to its length. 

Example. — Required the length of an arc ah c oi 30 degrees, 
the radius being 9 feet. 

3.1416X9=28.2744. 

Whence as 180° : 30 :: 28.2749 : 4.7124, the length of arc. 

Problem XXVII. 

170. The span or extent of a building, mid the height or pitch 
of its roof being given, to find the length of the rafters neces- 
sary for such roof. 

The general form of roofs is two right angled triangles, having 
but one common perpendicular between them, as in Fig. 44, 
where klis the extent of the building, m n the height of the roof, 
and k m the length of the rafter required, which length, it will 
be seen, is the length of the hypotenuse of the right angled 
triangle k n m. 

Rule. — To obtain it, add the square of the perpendicular m n 
to the square of the base or half span k n, and extract the square 
root of the sum, which will be the hypotenuse required. 

Note. — This process must be used for measuring roofs that are 
inaccessible for want of a ladder or staircase. The extent k I can 
be obtained on the ground and halved; the perpendicular m n 
may be got by counting the courses of brickwork from tz to ?7i, 
or by holding up a measuring rod on a high pole, or by means 
of trigonometry. 

Problem XXVIII. 

171. To find the area or superficial contents of a square or 
parallelogram; or any figure bounded by two right lined 
parallel sides, having right angles at the four corners. 

Rule. — Multiply the length by the breadth, or the dimensions 
of any one side by the dimensions of another at right angles to 
it, using the same denomination of measure in both instances, and 
the product will be the area in square dimensions of the same 
denomination. 

Example. — Find the superficial area of a wall 6 feet 6 inches 
high and 21 feet long. 



ON THE PRINCIPLES OF MENSURATION. 91 

Decimally. Duodecimally. 

21 21 

6.5 6 ft.6 In. 



10.5 126 

126 10 6 



136.5 feet, ans. 136 ft.6 in., ans. 

No examples will be given of the problems which follow, as 
they may all be worked in a similar manner. 

Problem XXIX. 

172. To find the area of any rhombus or four-sided figure, in 
ivhich the opposite sides are parallel right lines, but the 
angles not right angles, Fig. 43. 

Rule. — Erect a perpendicular^ i on any part of any side g h; 
measure the distance of two opposite sides upon that perpendicu- 
lar, and multiply by the length of either side that is perpendicular 
to g i. 

Problem XXX. 

173. To find the area of a triangle or gable end of a building. 
Rule. — Multiply the length of one of the sides o p in either 

triangle of Fig. 46, as a base, by the length of a perpendicular 
q r falling upon it, from the height q of the apex of the triangle, 
and half the product will be the area; or. 

The whole product obtained by multiplying one side into half 
the perpendicular height of the apex, will give the same result. 

Problem XXXI. 
174. To find the area Of a regular trapezoid. Fig. 45. 

Rule. — Add the top measure r s, to the bottom measure tv, and 
take half the sum for a mean, which multiply by the perpendicu- 
lar height uw, and the product will be the area; or. 

Multiply the top and bottom by the height, and take half the 
product. 

This problem applies to the measurement of canal cutting when 
the work is wholly excavation, the two side slopes make equal 
angles with the bottom, and the two banks are of equal height. 

Problem XXXII. 

175. To find the area of a trapezium, or four-sided right lined 
figure, in which no tivo sides need be equal or parallel to 
each other, as x, y, z, a. Fig. 47. 

Rule. — Draw a diagonal line x ij, uniting two opposite angles, 



92 ON THE PPaNCIPLES OF MENSURATION. 

and converting the figure into two triangles; from the angles a 
and y, let fall perpendiculars to cut the diagonal for the purpose 
of obtaining the height of the two triangles; measure them sepa- 
rately by Prob. XXX., and their sum will be the area sought. 

In I^ig. 48, X z is the diagonal, and the side yx is at right an- 
gles to it, therefore x y z is a right angled triangle, and its side 
xy gives its height without any other perpendicular; and, conse- 
quently, only one need be drawn from the point a, for measuring 
the triangle x a z. 

Note. — This is one of the most important problems in mensu- 
ration, and applies to a number of cases in building, land survey- 
ing, canal cutting, &c. 

Problem XXXIII. 
176. To find the area of a circle. 

Rule. — Square the diameter, and multiply the result by the 
decimal 0.7854; or, 

Square the circumference and multiply by 0.07958. The pro- 
duct, in either case, will be the area. 

For the area of a semicircle proceed as if it was an entire cir- 
cle, but only take half the product. 

Note. — This rule is used in deducting circular openings in 
walls, and the semicircular arches over doors and windows, and 
in a variety of other cases. 

Problem XXXIV. 

177. To find the area of a flat annulus or ring^ or the space 
inclosed between two concentric circles, as in Fig, 49. 

Rule. — Find the area of the two circles separately, (by last 
problem,) subtract the smaller from the larger, and the remain- 
der will be the area sought. 

Or multiply the sum of their diameters by their difference, and 
the product by 0.7854. 

This applies to the superficial measurement of the ends or 
faces of all circular and semicircular arches. 

Problem XXXV. 

1 78. To find the area of a sector of a circle or figure^ like 
c d Cy Fig. 50, in which d is the centre of the circle. 

Rule. — From the dimensions given, calculate the sector as if 
it was an entire circle, and then state this proportion: 

As 360° is to the number of degrees in the sector, so is the area 
of the whole circle just found, to the area of the sector. 



on the principles of mensuration. 93 

Problem XXXVI. 

179. To find the area of the segment of a circle^ or the space 
contained within any arc of a circle^ and the chord of that 
arCf (as at/, in Fig. 50.) 

Rule. — Proceed as in the last problem to find the area of the 
sector, and from that subtract the area of the triangle cde, form- 
ed by the chord and two radii, and the remainder will be the area 
of the segment sought. 

Problem XXXVII. 
180. To find the area of an ellipse. 

Rule. — Multiply the transverse by the conjugate diameter, 
and the product by 0.7854, as in the circle. 

Note. — From this the surface of elliptical arches may be found, 
following the process given in Problem XXXIV. 

OF POLYGONS. 

181. Polygons are usually spoken of as manj?" sided figures, 
although the strict meaning of the word is many angled, and 
they are divided into two classes, called regular and irregular. 

A regular polygon is a figure bounded by several equal right 
lines, which meet in angular points, which points are disposed 
in the circumference of a circle. 

An irregular polygon is also bounded by several right lines 
which meet in angular points; but the lines are not equal in 
length, nor are the angles arranged in a circle. 

182. Polygons may have any number of sides and angles with- 
out limitation; but, in general, when this figure is spoken of or 
used, the regular polygon of a few sides is referred to, and the 
figures are frequently some of the following: 

Multipliers, 

The Trtgon or Triangle, having 3 angles and 3 sides, - 0.4330127 

Tetragon or Square, having 4 angles and 4 sides, - 1.000000 

Pentagon, having 5 angles and 5 sides, - - 1.7204774 
Hexagon, „ 6 „ and 6 „ (See JVg. 20, P/./.) 2.5980762 

and 7 „ - - 3.6339126 

and 8 „ (See Fig. 19.) 4.8284272 

and 9 „ - - 6.1818240 

and 10 „ - . - 7.6942088 

and 11 „ - - 9.3656411 

and 12 „ - - 11.1961524 



Heptagon, „ 7 

Octagon, ,, 8 

NONAGON, „ 9 

Decagon, „ 10 

Undecagon, „ 11 

Dodecagon, „ 12 



The column of multipliers is for the purpose of obtaining the 
areas of the polygons against which they stand. For this pur- 
pose, square any one side, and multiply by the number against 



94 ON THE PRINCIPLES OP MENSURATION. 

the kind of polygon under examination, when the product will 
be the area required. 

Polygons are less frequently used than formerly. They were 
of constant occurrence in regular fortifications. Their use is now 
confined to the fluting of columns; the construction of panoptic 
prisons; the towers of Gothic buildings; the spires of churches, 
and a few other objects. 

Problem XXXVIII. 

183. To find the area of a regular polygon of any number of 

sides. 

Rule. — Multiply the perimeter, or sum of the length of all 
the sides, by the length of a perpendicular, let fall from the cen- 
tre of the circle to any side, and half the product will be the area 
sought. 

This depends upon the regular polygon being composed of a 
series of equal and contiguous triangles, all having the centre of 
the circle for a common apex. See g h i, Fig. 51. The sum of all 
the sides is, therefore, equivalent to the sum of all the bases of 
the triangles, and the perpendiculars h /r, is the height of these 
triangles; consequently this measurement depends upon that of 
the triangle. Prob. XXX. 

Problem XXXIX. 

184. To find the area of an irregular polygon. 

Rule. — Draw or set out such diagonals in the figure as will 
divide it into trapeziums or triangles, or both, as shown by the 
lines in Fig. 52. Find the area of each separately, and the sum 
of the whole will be the area of the figure. 

Problem XL. 

185. To find the area of a long irregular figure. 

Rule. — Take the breadths in several places, at equal distances 
from each other; add all these breadths together, and divide the 
sum by the number of measurements taken, to obtain a mean 
breadth; then multiply the mean breadth by the length of the 
figure, and the product will be the area. 

Example. — Required the area of the irregular figure ah c d, 
Fig, 53, the breadth of which at a c is=8.1, at e=7.4, at/=9.2, 
at ^=10.1, and at 6 d=8.Q, and the length from c to d=h9. 

Here five breadths are taken, the sum of which are 43.4; and 
this sum, divided by 5, gives 8.68 for a mean breadth, and 8.68 
X39 gives 338.52 for the area of the figure. 



ON THE PRINCIPLES OF MENSURATION. 9^ 

This problem is of constant occurrence in land surveying for 
what is called measuring offsets. 

The foregoing problems comprehend most of the cases that 
usually occur in measuring land or artificers' work, when the 
superficies only has to be examined; and those that follow relate 
to solid or cubic measure, which must next be considered. 

solid measure. 

Problem XLI. 
186. To find the solid contents of a cube. 

Rule. — Find the area of one side by Problem XXVIII. , and 
multiply that by the length of any side in the same denomination 
of measure, when the product will be the solidity required. 

Example. — How many cubic inches are contained in a cubic 
foot? 

12 inches X 12 inches gives 144 inches for the area of one side, 
and that product multiplied by 12, the length of one side, gives 
1728, the number of cubic inches required. 

Problem XLII. 
187. To find the solidity of a parallelopipedon. 

Rule. — Multiply the length, breadth and depth, or altitude, 
continually together; or, if more convenient, ascertain the area 
of a transverse section of that which has to be examined, and 
multiply that by the length for the solid contents. 

Example. — What is the solid contents of a piece of timber 12 
inches square and 3 feet long? 

The sectional area is 1 square foot or 144 square inches by last 
problem; multiply, therefore, 144 by 36, the number of inches in 
3 feet, because the same kind of measure should be used in both 
cases. The product will be 5184 for the number of cubic inches 
contained in the piece. To reduce this quantity into cubic feet, 
divide by 1728, the number of cubic inches in a cubic foot. 

Note. — This problem is of most extensive use, and applies 
in a great variety of cases. Thus, if a wall is 40 feet long, 15 
feet high, and 3 bricks, or 27 inches, in thickness, how many 
cubic feet of brickwork does it contain? 

40 feetx 15 feet gives 600 feet for the area of the surface, which 
multiply by 2.25, (because 27 inches are 2\ feet,) and the result 
will be 1350.00 cubic feet. 



96 on the principles of mensuration. 

Problem XLIII. 

188. To find the solidity of a prism, cylinder, or other solid, 

having parallel sides. 

Rule. — Multiply the area of the base by the height, and the 
product will be the solid contents. 

Example. — Required the solid contents of an equilateral tri- 
angular prism, each side of which is 2-J feet, and whole height is 
12 feet. The area of any equilateral triangle may be found by 
squaring one of its sides, and multiplying that square by 0.433013 
(182); and this product multiplied by 12 feet, the height, will 
give the solid contents. 

A consequence of this problem is, that all bodies which have 
parallel sides, and are therefore of the same size from top to bot- 
tom, will have equal solid contents, whatever their forms may 
be, whenever their bases and altitudes are alike. 

Problem XLIV. 
189. To find the solidity of a cone or pyramid. 

Rule. — Multiply the area of the base by the perpendicular 
height of the cone, and one-third of the product will be the solid 
contents required. 

Note. — If a cone, find the area of base by Problem XXXIII. 
If a pyramid of any number of sides less than 13, the area may 
be found by the Table of Multipliers. (Par. 182.) 

Problem XLV. 
190. To find the solidity of the frustrum of a cone or pyramid. 

Rule, when the diameters of the two ends and the height of 
the frustrum of a cone are given — Divide the difference of the 
cubes of the diameters of the two ends by the difference of the 
diameters, and this quotient being multiplied by .7854, and again 
by one-third of the height, will give the solidity. 

Rule for the frustrum of a pyramid, the sides of the base and 
top, and the height being given. — Add to the areas of the two 
ends of the frustrum the square root of their product, and this 
sum being multiplied by one-third of the height, will give the 
solidity. 

Problem XLVI. 

191. To find the solidity of an irregular wedge. 

Note. — If it is regular, or has parallel ends, it is a triangular 
prism, and is found by Problem XLIII. But if the ends are not 
parallel, then 



ON THE PRINCIPLES OF MENSURATION. ' 97 

Rule. — To the length of the edge of the wedge a b, Fig. 54, 
add twice the length of the back or base d e; multiply this sum 
by the height a p, and then by the breadth c d, of the base, and 
one-sixth of the last product will be the solid contents. Therefore, 

Hap the height=14, a b the edge=21, d e the length of base 

=32, and c d the breadth=4j, the solid contents will be thus 

found : 

5355 
21+64 (32X2)=85; and 85x14x41=5355; and ——=892.5 

cubic inches, the solidity required. 

Problem XL VII. 

192. To find the solidity of a prismoid, or tapering pedestal y 

Fig. 55. 

Rule. — Add into one sum the areas of the two ends, and four 
times the middle section, parallel to them; and this sum, multi- 
plied by one-sixth of the height, will give the contents. 

Note. — The length of the middle section is equal to half the 
sum of the lengths of the two ends; and its breadth is equal to 
half the sum of the breadths of the two ends; consequently the 
middle section so obtained gives a mean sectional area of the 
prismoid, and may be multiplied by the height, as another means 
of obtaining the solid contents. 

Problem XLVIII. 

193. To find the solidity of a sphere or globe. 

Rule. — Multiply the cube of the diameter by 0.5236, and the 
product will be the solidity. 

Problem XLIX. 

1 94. To find the solidity of a spherical segment, or plano- 
convex portion of a sphere. 

Rule. — To three times the square of the radius of the base or 
flat side, add the square of the versed sine or height; then mul- 
tiply the sum by the height, and the product so obtained by 
0.5236, for the solid contents. 

Example. — Required the solid contents of a dome 16 feet in 
diameter, rising 4 feet from its chord. In this case the radius of 
the base is 8 feet, therefore, 

8^X3-f 4*^=208; and 208X4X0.5236=435.635 feet, the solid con- 
tents required. 
13 



98 on the pkinciples of mensuration. 

Problem L. 
195. To find the solidity of a spheroid^ or solid ellipse. 

Rule. — Multiply the square of the transverse by the square of 
the conjugate diameter, and the product, multiplied by 0.5236, 
will give the contents. 

Problem LI. 
196. To find the solidity of a parabolic conoid. 

Rule. — Multiply the square of the diameter of the base by the 
height or length of the axis, and the product by 0.3927. 

Note. — Two such solids conjoined base to base, form a para- 
bolic spindle. 

Problem LII. 

197. To find the solid contents of a cylindrical ring. 

Rule. — To the diameter of the cylinder of which the ring is 
formed, add the extent of the inner diameter of the ring. Then 
multiply the sum by the square of the thickness or diameter of 
the ring, and the product by 2.4674, (which is one-fourth of the 
square of 3.1416,) and it will give the solidity. 

Example. — Required the solidity of a ring, the thickness of 
which is 2 inches, and inner diameter 12 inches? 

12+2x2^=56; and 56X2.4674=138.1744 inches. 

Problem LIII. 
198. To find the superficies or solidity of the regular solids. 

Rule for superficies. — Multiply the square of one linear 
edge by the number in the table below, opposite the given solid, 
and headed surfaces, and the product will be the superficies. 

Rule for the solidity. — Proceed as before, taking the tabu- 
lar number, headed solidity, and the product will be the solidity. 

199. Table of surfaces and solidities of the regular hodies when the 

linear edge is 1. 



No. of sides. 


Names of solids. 


Surfaces. 


Solidity. 


4 


Tetrahedron 


1.73205 


0.11785 


6 


Hexahedron 


6.00000 


1.00000 


8 


Octohedron 


3.46410 


0.47140 


12 


Dodecahedron 


20.64573 


7.66312 


20 


Icosahedron 


8.66025 


2.18169 



200. Examples. — Required the superficies and solidity of a 



ON THE PRINCIPLES OF MENSURATION. 99 

tetrahedron, the linear edge or side of which is 3 inches. See 
Fig, 56. 

1.73205x3^=15.588, &c. for its superficies. 
0.11785x3^= 3.18195, for its solidity. 
Note. — The hexahedron is the same thing as the cube. 

201. Required the superficies and solidity of an octohedron, 
Fig. 57, the linear side of which is 2 inches. 

3.46410x2^=13.85640, for the superficies. 
0. 47140 x22= 3.77120, for the solidity. 

202. Required the superficies and solid contents of a dodeca- 
hedron, Fig. 58, whose linear edges are 2 inches. 

20.64573x2^=82.58292, for the superficies. 
7.66312x22=61.30466, for solidity. 

203. Required the superficies and solid contents of an icosa- 
hedron. Fig. 59, whose linear edges are 2 inches. 

8.66025X2^=34.64100, for superficies. 
2.18169x23=17.45352, for solidity. 

204. or CONVEX AND CONCAVE SUPERFICIAL MEASUREMENT. 

This is frequently necessary for determining the quantity 
of stonemasons, plasterers, or painters' work expended upon 
curved surfaces, such as domes, niches with arched heads, 
spheres, or portions of them, and various other figures introduced 
into buildings, for ornamental purposes. 

No rules are given for concave surfaces, because no concave 
surface can exist, but wliat we may conceive a convex body that 
will exactly fit it and fill it up; consequently the convex surface 
will, in all such cases, be exactly equal to the corresponding con- 
cave one, and whenever a concave surface has to be determined, 
it is done by calculating the convex surface that so corresponds 
with it. 

Problem LIV. 
205. To find the convex surface of a cylinder. 

Rule. — Multiply the circumference by the length of the cylin- 
der, and the product will be the convex surface required. 

Note. — The upright surface of any prism may be found in the 
same manner. 

Problem LV. 

206. To find the convex surface of a right cone or pyramid. 

Rule. — Multiply the perimeter, or circumference of the base, 
by the slant height, or length of the side of the cone; and half 
the product will be the surface. 



100 on the principles of mensuration. 

Problem LVI. 

207. To find the convex surface of a frustrum of a cone or 

pyramid. 

Rule. — Multiply the sum of the perimeters of the two ends 
by the slant height or side of the frustrum, and half the product 
will be the surface required. 

Note. — This problem applies to measuring the surfaces of all 
columns which taper gradually from their base. 

Problem LVII. 

208. To find the convex surface of a sphere or globe. 

Rule. — Multiply the diameter of the sphere by its circum- 
ference; or, multiply 3.1416 by the square of the diameter, and 
the product will be the convex surface required. 

Note. — The convex surface of any zone, or segment of a sphere, 
may be found, in like manner, by multiplying its height or pro- 
jection by the whole circumference of the sphere. 

Problem LVIII. 

209. To find the convex surface of a cylindrical ring. 

Rule. — To the thickness of the ring, or diameter of the cylin- 
der, of which it is composed, add the inner diameter of the ring; 
multiply this sum by the thickness, and the product by 9.8696, 
(which is the square of 3.14159,) and it will give the superficies 
required. 

210. It is believed that the above rules will meet every case 
and form that the Engineer, Architect, Surveyor, or Artificer 
may have to measure, except in very extraordinary instances; 
and it may appear that the next step should be to show the prac- 
tical application of them to their several purposes, with which it 
was, at first, intended to close the present chapter. But inas- 
much as many technical phrases occur in the mensuration of ac- 
tual work, and these have not yet been explained, and consequent- 
ly could not be understood, the better and more useful course 
appears to be, to describe the several varieties of work in the 
first instance, and to conclude each article as it is completed with 
the rules that apply to its measurement, making references, when- 
ever necessary, to the foregoing problems, as by this arrange- 
ment, it is believed, no difficulties can occur. This mode of pro- 
ceeding will be accordingly adopted. 



101 



CHAPTER IV. 



ON LAND SURVEYING. 



211. Land surveying, in its detail, is nothing more than a 
practical application of some of the principles described in the 
last chapter, but used on so large a scale that the ordinary instru- 
ments of measuring, and methods of using them, will not apply 
without variations and precautions, which it will be the object of 
the present chapter to describe. It comprehends not only the 
measurement of land, by which its quantity is ascertained, but 
the plotting, or drawing of maps or plans, that will repre- 
sent the precise forms, relative positions, and proportional dis- 
tances of all the objects that occur upon the ground, all of which 
should be laid down upon the map with such exactitude that it 
becomes a perfect representation of what occurs in nature, and 
should admit of the proportional distances of objects being mea- 
sured and ascertained by the compasses and scale, as correctly as 
if they were actually measured on the surface of the earth. 

212. Land surveying is usually considered as a distinct pro- 
fession in the old settled and thickly populated countries; and the 
regular land surveyor not only measures and ascertains the pre- 
cise quantity of land, and prepares a map or plan of it, but he is 
also an appraiser. He sets a value on the several varieties of soil 
according to its location; he measures and values the timber and 
standing crops, as well as the buildings, fences, and improve- 
ments upon the soil; and should be able to give his employer, 
not only the quantity and position of his land, but the actual 
value of every thing that occurs upon an estate. 

213. Land surveying does not properly belong to, or form a 
part of, the duties of the Civil Engineer; but, in many instances, 
he is unable to lay down his plans without its assistance, espe- 
cially for the formation of roads or canals. In England, when 
such works have to be set out in the first instance, it is always 
customary to employ a land surveyor to make a map or plan of 
the route, before the Engineer begins his operations, further than 
by going once or twice over the ground and pointing out the line 



102 ON LAND SURVEYING. 

proper to be surveyed. The reason for this course of proceeding 
is — 1st. That the land surveyor usually follows no other occu- 
pation, and possesses all the necessary instruments; and by 
constant habit and application to the same pursuit, acquires a fa- 
cility and expedition, that the Engineer, whose attention is con- 
stantly drawn to a great variety of objects, can hardly be expect- 
ed to possess; and, 2ndly. The constant attention of the land 
surveyor to the same business, enables him to furnish a plan for 
a much less sum of money, than if it was prepared by the Engi- 
neer, who, on account of the extent and versatility of his know- 
ledge, always receives a higher rate of compensation for his time 
and services than the mere land measurer. Some of the princi- 
pal Engineers keep clerks or assistants in their offices, who de- 
vote themselves entirely to land surveying and mapping, for the 
purpose of producing plans for their principal. 

214. It frequently happens that good maps, to large scale, may 
be purchased, or that private local plans of estates may be pro- 
cured among the land owners upon a line, which afford material 
assistance, and may save the expense of a primitive survey. The 
Engineer, in this case, can copy them by tracing-paper, (90,) and 
afterwards by altering and making the scales to assimilate, may 
recopy them into one general and connected plan, and the Panta- 
graph before described, (103,) will be found a most convenient 
instrument for copying and reducing, or extending plans for such 
purposes. 

215. In w^hatever manner the primitive map or plan of the 
country may have been procured, it is the duty of the Engineer 
to compare and examine it with the real ground, to prove its cor- 
rectness; and likewise to stake, or otherwise set out his works 
upon the ground; and to introduce them into such map, as the 
staking or setting out proceeds, so tliat the marked map may 
become a perfect resemblance, as to form and position, of the 
work that has to be executed. 

It frequently happens in new or thinly populated countries, 
that the advantage and assistance of a land surveyor cannot be 
procured. Or the Engineer, with a view to correctness, may 
wish to execute his own survey, and it is hoped that the direc- 
tions which follow will enable him to do so. 

216. Land is always measured lineally, by miles, furlongs, 
chains, poles, yards, feet, links and inches; and the following 
table will show the proportions these several lineal measures bear 
to each other. 



ON LAND SURVEYING. 103 

Table of Jlmerican and English Lineal Measures of Land, 



in. 

7.92 — 


1 link 








12 — 


1 17 


1 foot 








36— 


4 ^ 
1 1 


3— 


1 yard 








198— 


25— 


16-1— 


5i_ 


1 pole 








792= 


100— 


6Q — 


22— 


4— 


1 chain 






7920 


1000 


660— 


220— 


40— 


10— 


1 furl. 




63360 


8000 


5280 


1760 


320= 


80— 


8— 


1 mile. 



217. The following table exhibits in like manner the propor- 
tions that the Square Measures of Land bear to each other. 



9 feet 


1 yard 




^ 




272i 


301 


1 perch 








4356 


484 


16 


1 chain 








10890 


1210 


40 


2-J 


1 rood 






43560 


4840 


160 


10 


4 


1 acre 




27878400 


3097600 


102400 


6400 


2560 


640 


1 mile 



218. The words perch, pole and rod, are used synonymously 
in land measuring, and are all the same lineal measure; but the 
rood is a square measure, equal to the fourth of an acre. The 
surface of land is estimated in acres, roods and perches, and occa- 
sionally in square yards and feet, when great nicety is required. 

219. The instruments absolutely necessary for the ordinary 
purposes of land measuring are, a chain and arrows, or markers; 
a few picket or station staves, or sight rods; some small stakes 
and a mallet; a pair of offset staves; a surveyor's cross, and a 
pocket compass. And to these must be added, for more accurate 
and extended surveys, a Circumferenter or Theodolite. Another 
simple instrument, called a plain table and sights, is also very 
convenient for small surveys, as by its means the survey and plan 



104 ON LAND SURVEYING. 

are made at one operation. In all cases a small blank book, called 
a field book, and pen and ink, are necessary for recording obser- 
vations; and a measuring tape, which rolls into a leather box by 
a small brass winch, and is divided into links on one side, and 
yards and decimals of a yard, or even into feet and inches, on 
the other, will prove very useful for taking short lengths. Such 
tapes are made in 2 or 4 pole lengths, and are very portable. 

220. The measuring chain is usually made of strong iron wire, 
with a handle at each end, by which two persons called chain 
bearers carry it. The one that precedes is called the leader, and 
the other the follower. Any one can lead a chain, but some 
skill and attention is necessary in the follower, because he has to 
direct the leader in his movements, and to give him other instruc- 
tions. The arrows or markers are always 10 in number, and are 
composed of pieces of strong iron wire, about 15 inches long, 
sharpened at the point, and bent into an eye at the opposite end, 
for the convenience of stringing them upon a cord or leather 
strap to carry them and prevent their being lost. A piece of 
scarlet cloth should be attached to the eye of each arrow to render 
them distinctly visible when stuck in the ground, particularly in 
the grass, as without this precaution much time is frequently lost 
in searching for them. In using the chain, a peg or stake is 
driven into the ground to mark the starting point from w-hich the 
measurement begins, and the whole of the 10 arrows are given 
to the leader. The follower stands at the starting stake, and 
places, his end of the chain in contact with it, or rather holds it in 
his hand over it, while the leader proceeds with the other end of 
the chain in the desired direction, until it becomes nearly stretched 
or extended, when the follower gives the word halt, and the 
leader stops. The chain is now lifted from the ground and 
stretched, when the follower places its end carefully to his mark; 
and having observed that the chain is in the right direction, and 
not deflected by bushes or other obstacles, he gives the word down, 
and the leader places the chain upon the ground, keeping it tightly 
stretched. The follower having observed that all is right, calls 
out mark, when the leader sticks one of his arrows into the 
ground close to his end of the chain, and the first chain is com- 
pleted. The bearers then both proceed onwards, and at this time 
the chain should be slightly strained, so as to take ofi'its bearing 
against the ground, otherwise it will be liable to get entangled 
with weeds, or to wear out, or at any rate to become elongated. 
The follower must look at some mark to guide the proper direc- 
tion of the measurement, and will accordingly order his leader 
to the right or left to preserve that line. He must likewise take 
care to so direct the movements of his leader, that the chain in its 



ON LAND SURVEYING. 105 

progress may not rub against the arrow that has been left in the 
ground; for if that gets knocked down or displaced, the operation 
must commence again. Having proceeded in this manner until 
the follower arrives at the arrow that was left, he again halts his 
leader, adjusts the chain, and orders a second mark to be made; 
and that done, he takes up the first arrow and retains it, and so 
of others in succession, until the whole 10 arrows of the leader 
are exhausted and have come into his possession. The chain 
remaining stretched on the ground, the leader now comes back 
to the follower to take up the arrows he has picked up, and the 
follower registers this operation by an entry in his book, or what 
is more common in the measurement of long lines, by making a 
knot in a string that he has previously attached to his button-hole 
for that purpose, each knot standing for 10 chains. In this way 
errors seldom arise; but some Surveyors, to guard against them, 
and insure the certainty of not having an entire line to measure 
over again from mistakes, use the precaution of driving a perma- 
nent peg or stake at every 10 or 20 chains, or other stated regular 
distances. 

221. Simple as the common measuring chain may appear to 
be, it is nevertheless a beautiful contrivance of the celebrated 
mathematician, Edmund Gunter, who lived in London in the 
seventeenth century, and is most admirably suited to the pur- 
poses for which it is intended. It is 22 yards, or 66 feet, long, 
and is divided into 100 equal links, so that links are decimal 
fractions of a chain. The acre contains 4840 square yards, and 
the chain being 22 yards long, if its length be squared, it produces 
484 square yards, or the tenth of an acre; consequently 10 square 
chains are an acre, and as each chain contains 100 links, so an 
acre will always be equal to 100,000 square links. In setting 
down or recording measurements taken with the chain, the num- 
ber of links are placed as decimals after the number of chains, so 
that a piece of land containing 16543 square chains and 75 links 
would be set down as 16543.75, and on taking away the deci- 
mal point, the number would be altered to 1654375, which would 
express the total number of square links contained in the land. 
But if the measure of a piece of land taken in square links is 
divided by 100,000, or the number of links in an acre, or, which 
is the same thing, if the 5 right hand numbers are pointed off as 
decimals, (which is the same as dividing by 100,000,) the figures 
will at once express the acres and fractions without further cal- 
culation. Thus cutting of the five decimals gives 16.54375, or 
16 acres, and the decimal .54375. 

222. The acre consists of 4 roods, therefore if this decimal be 
multiplied by 4, it will become 217500 links; and now, if 5 de- 

14 



106 ON LAND SURVEYING. 

cimals be again pointed off, it shows that the fraction is worth 2 
roods and .17500; and again multiplying this fraction by 40, the 
number of perches in a rood, we shall obtain 300000, and now 
pointing off 5 decimals, leaves 3 perches without a fraction, and 
shows that such a piece of land would contain exactly IG acres, 
2 roods and 3 perches. This example shows at once the process 
that must be resorted to for converting quantities taken in chains 
and links into acres, roods and perches, while the remainder, if 
any, will be square links. 

223. In using the chain, it must be borne in mind that the 
handles at its tvvo ends count into its length; and for the facility 
of counting the links, small brass indices are attached at certain 
points among the links. Thus the 10th link from each end has 
a single point or brass finger attached to it; 20 links from each 
end has an index with 2 points; 30 links one with 3; 40 links 
one with 4; and 50 links, or the middle of the chain from each 
end, is marked hy a small round brass plate; so that by looking 
for these marks the distance from either end is given upon inspec- 
tion, and a portion only of the next 10 links has to be counted. 

Many persons, for the sake of having a light chain to carry, 
purchase those that are made of thin wire; but they can never be 
depended upon, because the strength of the wire should be such 
as to permit the chain to be stretched without any fear of any of 
the links opening or expanding, an inconvenience to which even 
the strongest chains are liable. No chain should therefore be 
used many days in succession without an examination; and this 
is one use of the offset staves, which are 6 feet 7.2 long, and are 
divided into 10 equal joarts of the same length as links; and the 
surveyor should have a small hammer for beating or closing up 
the links and thus adjusting his chain, for upon its accuracy all 
his operations must depend; and in the more extensive operations 
of trigonometry the correct measurement of a good base line is 
of vital importance to the success of the whole operation. 

224. Chains are sometimes made only 2 poles long, and are 
convenient in woody countries. They are called half chains. 
They should not be used when there is room for a full chain, 
because they occasion loss of time and lead to errors, being some- 
times set down as whole chains. 

225. No one without actual experience can conceive the great 
difficulty that occurs in setting out and measuring right lines of 
great length in real practice. Indeed, with a com»mon chain, and 
such apparatus as land surveyors usually employ, it is quite im- 
possible to do it, so as even to approach to mathematical accuracy; 
therefore every precaution should be taken by the surveyor to 
make his operations as correct as possible. The principal sources 



ON LAND SURVEYING. 107 

of error in land measuring proceed from the chain not being car- 
ried and stretched in a perfect right line; from the chain being 
unequally pulled or stretched when laid down; from the surface 
of the ground upon which it is laid before marking being uneven, 
which makes the chain measurements shorter than they really 
should be; from the arrows or markers not being placed exactly 
at the ends of the chain, or being fixed in an exact perpendicular 
direction in the ground; and lastl}?", from the expansion and con- 
traction of the metal itself, which will vary the length of the 
chain w^ith difierent temperatures. Most of these circumstances 
may, however, be much diminished by careful operators. 

226. In conducting great trigonometrical operations, in which 
the success depends in great measure upon the accuracy with 
which the original base line is measured, no time, labour, or ex- 
pense is spared in making it as perfect as possible. If chains are 
used, they are composed of long links, and the chain itself is 
strained by equal weights, in every case acting over pullies fixed 
on the tops of pedestals attached to the ground, and made truly 
level on their tops, so that the chain does not rest upon the 
ground, and the quantity of its sag or depression is ascertained. 
At other times cylindrical glass rods have been made use of, 
supported at such short distances upon levelled stakes as to pre- 
vent their sagging, and having their ends rounded, polished, and 
laid in contact with each other. Glass is selected for this pur- 
pose because less liable to bend, or to expand or contract by heat, 
than almost any other material that could be used. Such precau- 
tions are, however, too delicate, costly and tedious, to be attempt- 
ed in the ordinary measurement of land. 

227. The first thing the ordinary land measurer must attend 
to, before he attempts to use the chain, is the setting out of as 
good or straight a right line as possible upon the ground; and 
this is done by means of the station or picket staves, or sight 
rods, of which every surveyor should possess at least half a dozen. 
They are nothing more than straight cylindrical or slightly taper- 
ing sticks, shod with iron points at their bottoms,, for the facility 
of sticking them upright into the ground. They should be per- 
fectly straight, and at least 6 or 7 feet high; and if painted white, 
will be more distinctly seen at great distances. A saw-scarf or 
slit should be cut 3 or 4 inches down each staff", for the purpose 
of sticking in a piece of white paper to render them visible at 
great distances, particularly in woody places, or to mark particu- 
lar rods for particular purposes. 

228. To set out a straight line upon the ground, the surveyor 
must first mark the two ends of the required line by fixing a 
picket-staff" at each point; then standing a short distance behind 



108 ON LAND SURVEYING. 

either of the staves, he closes one eye, and looks by the side 
of the staff near to him at that which is distant, and in the mean- 
^time gets an assistant to fix up other intermediate staves at as 
nearly equal distances as can be guessed at without measuring, 
taking care that they shall be so placed in a direct line as to ap- 
pear to assimilate and combine with the two first rods set up; or 
in other words, that the nearest rod shall hide or cover all the 
intermediate ones when looking from the first towards the last. 
This adjustment, as to position, is easily affected by making 
signals with the hands to the assistant, by which he is directed to 
move his staff to the right or to the left of the line before fixing 
it in the ground. The picket staves rem.ain in their places until 
that line is done with, and then they are moved for setting out 
another, unless the two extreme staves should require to be left 
standing for other uses. 

229. Every line that has to be measured by the chain should be 
previously set out In this way, whenever its length exceeds two or 
three chains, and the chain-bearers will then have no difficulty in 
moving in right lines, since they must keep the chain constantly 
in contact with the staves, and coincident with the line so set out. 
In this same way are all diagonals from one corner of a field to 
another, or from one part of an estate to another, to be set out 
upon the ground. This operation is technically called boning 
a line, and the examination of its truth is called, seeing if it bones 
well; terms indicating the goodness or perfection of the line, 
derived from the old Norman French, in common with a great 
number of other names used in architecture and engineering. 

230. The next essential instrument for ordinary land measuring 
is the surveying cross, which is intended only for setting out 
right angles upon the ground, either for the purposes of survey- 
ing, or commencing buildings that are to have square corners. 
This instrument, as it is usually made by the instrument-makers, 
is shown in perspective at Fig. 60, Plate II. It is made wholly 
of brass, and consists of four upright plates ah c and c/, called 
sights, which are fixed at right angles upon a cross-shaped piece 
e, on the under side of which is a socket / to receive the staff 
g^ upon the top of which the cross may be fixed by tighten- 
ing the screw h. The staff g should be nearly equal in height 
to the observer's eye, to prevent stooping; and its lower ex- 
extremity terminates in a sharp iron point for sticking it in the 
ground. The sights d and c are each perforated by a very nar- 
row slit, extending nearly from top to bottom, to the intent that 
when the eye is applied to look through them for observing an 
object, it may range upwards and downwards, but cannot be 
moved laterally. The opposite sights a and h are perforated by 



ON LAND SURVEYING. 109 

long square openings, over the middle of which a horse hair or 
fine wire is extended in a vertical direction; and the instrument 
must be so adjusted by the maker, that when the eye of an ob- 
server is applied to the slit at m, and sees the distant object k 
covered or bisected by the wire in <z, and another observer apply- 
ing his eye at n, and finding the wire of 6, in like manner cover- 
ing the object i, the two dotted lines of sight m A: and ni, must 
be correctly at right angles with each other. Hence a right an- 
gle may at any time be set out upon the ground by such an instru- 
ment; thus suppose the object k to be fixed, and that the staff of 
the instrument is stuck into the ground and turned round until 
that object is seen from m, and is exactly covered by the wire in 
a. The instrument now remaining stationary, the observer ap- 
plies his eye to n, and directs his assistant to fix a picket-rod in a 
distant position, so that it shall be seen covered by the wire of 6. 
It will be evident that the only position in which that rod can be 
set down, so as to fulfil the conditions, will be at i, and that the 
two sight lines m k and 71 i, must be at right angles to each other, 
crossing at the point where the staff is stuck into the ground, 
provided the staff has been set upright. 

In this instrument the opposite sights must be, at least, five or 
six inches apart, to prevent the wires coming within the limits of 
distinct vision when the eye is applied to the slits. The sights 
are usually made to unfix from the horizontal cross, by thumb- 
screws, for packing to travel; and the instrument is an expensive 
one, on account of the necessary perfection of workmanship, and 
difficulty of so adjusting the sights that they shall give precise 
right angles, in every direction in which they may be looked 
through: but, at the same time, it is not a convenient practical in- 
strument, on account of its liability to injury, for the sights are 
very liable to get bent by blows against trees or fences, or by con- 
tact with other instruments in carrying, and it may get out of 
truth by frequent packing and unpacking. It, therefore, requires 
frequent examination as to adjustment, and that is done in this, 
as in all other surveying crosses, by setting out a right angle with 
the sights in a fixed position, as above described, and then turning 
the instrument a quarter round, and seeing if it measures that 
same angle over again with equal precision. 

231. A surveying cross, that is very much used by practical 
surveyors, and is quite as effective, if carefully made, and much 
less costly, is shown Sit Fig. 61. It consists of a cube of any 
hard and well seasoned wood, fixed on the top of a pointed staff, 
as before. Two vertical cuts are made by a tenon saw on the top 
of the cube, exactly at right angles to each other, and they pro- 
ceed down to about three-quarters of the depth of the cube, leav- 



110 ON LAND SURVEYING. 

ing sufficient wood at the bottom to maintain all the parts firmly 
in their places. These saw cuts are the sights, and they are to 
be looked through and used exactly like the former instrument. 
A thin cap of wood may be fixed, by four screws, on to the top of 
the cube, and then there will be no danger of its breaking or 
warping. The same instrument might be formed out of a cylin- 
drical piece of wood, and would be more convenient to carry; 
but it is more difficult to make the cuts correctly at right angles in 
a cylinder than in a cube. A cylindrical form may, however, 
be given to the cube after the cuts are made and proved, or the 
vertical corners may be truncated or bevelled off, as indicated by 
the dotted lines in the figure. The only inconvenience attend- 
ing the use of this instrument, is its having so very narrow a field 
of view in a lateral direction; for nothing can be seen to the right 
or left of the direction of the cut; but this may, in some measure, 
be obviated by making two centre-bit holes through the cube, at 
the bottom of the cuts, to be looked through in the first instance. 
232. Both these instruments are troublesome, and sometimes 
tedious in their practical use, as will appear when their applica- 
tions are hereafter described. On this account the author con- 
trived a little instrument for his own purposes, and which he has 
used extensively, with so much satisfaction, that he believes no 
one will desire to use any other kind of cross, after having wit- 
nessed its convenience and expedition. It may be called the re- 
flecting surveying cross, and the idea of it arose from his having 
occasionally used a reflecting snuff-box sextant, set to 90°, for the 
purpose of taking offsets. The external appearance of this in- 
strument is shown at Fig. Q2. It consists of a circular box like 
a large snuff-box, from three to three and a half inches diameter, 
and about one and a quarter inches deep on the outside. An ob- 
serving or eye-slit is made in the side at a, and directly opposite, 
on the other side of the box, a round or square hole is made, as 
large as the width of the box will admit. This is dotted in at h, 
in the figure, because it would not be visible in the position of 
the box there shown. Another large hole is made in the side of 
the box at c, in a position exactly at right angles to a line that 
would join the centres of the other openings a and b. Fig. 63 
is a plan of the box with the lid removed, to show the relative 
positions of the holes, which are marked with the same letters a, 
b, c, and of the reflector d d, which is a strip of thin parallel look- 
ing-glass, the length of which is equal to the diameter, and its 
width equal to the depth of the box. The silvering is scraped 
oft' the upper half of this strip of looking-glass, in order that di- 
rect vision may take place through it; consequently if the eye 
E, be applied to the slit a, it will observe the distant object D, 



ON LAND SURVEYING. Ill 

by direct vision through the hole bf and upper unsilvered half of 
the reflector dd; while if another object R is at right angles to 
the line DE, it will be seen through the hole c, will be reflected 
by the lower silvered half of the mirror into the direction a, (be- 
cause the mirror is inclined 45° to DE,) and will thus appear to 
coincide with the object D. 

The reflector is fixed in its place by four angular blocks of 
cork or wood, glued into the inside of the box, as shown in I^ig. 
63, and its adjustment as to due angular position may be efiected 
by observing objects previously disposed in proper positions be- 
fore the glue becomes set and hard. If a slight correction of po- 
sition should afterwards be found necessary, it may be produced 
by cutting away a small portion of one of the pieces of cork, and 
introducing wedges opposite to it, which should be glued in to 
prevent their falling out. This done, the inside of the box is 
coloured dead black with lamp-black and thin glue, when the lid 
of the box may be permanently screwed down to prevent injury 
to the mirror. The three holes, or openings a b and c, may also 
be closed by thin parallel window glass, and then neither dust or 
any thing else can get into the box to injure it, even if carried 
open in the pocket. 

233. The last of the instruments named, as being necessary to 
the operations of ordinary land measuring, was a pocket-compass 
or magnetic needle, for the purpose of ascertaining the north, 
south, east, and west points of the land, or the cardinal points, as 
they are frequently called: and such a one may be a separate in- 
strument, or may be very conveniently included in the lid of 
the reflecting cross, Fig. 62. In small surveys the compass is not 
essential, because the sun is always due south at twelve o'clock; 
therefore, by holding a stick perpendicularly upon the ground at 
this hour, its shadow will give a north and south line with sufli- 
cient accuracy, and this is an expedient the land surveyor often 
resorts to, in the absence of his compass. 

234. Land surveying, when the estate or object of survey 
is not very extended, requires no other instruments than 
those above described, and their application to the purpose is 
very simple, for the operation is always conducted upon the 
principles laid down in Prob. XXXIL, (175,) and illustrated 
by Fig. 47, Plate II. That is to say, a diagonal is to be 
drawn from any one corner of a four-sided field to the angle 
most nearly opposite to it, so as to divide the field into two 
triangles, and then perpendiculars must be raised either upon 
that diagonal, or upon some side of the triangle for the purpose 
of obtaining its area. (Prob. XXX., Par. 173.) Thus, sup- 
pose a X y Zy Fig. 47, to represent an irregular four-sided field, 



112 ON LAND SURVEYING. 

which requires to be measured. The first operation will be to 
set out and bone the diagonal line x z, which is done upon the 
ground by a row of picket-rods; then the line x z must be 
measured by the chain and arrows; and suppose the result to be 
18.25 chains — this one measurement gives the bases of both 
triangles, because a? z is a common base to the two triangles z a x 
and z y X. Having thus got the length of both bases, the next 
object must be to get the height of the two triangles, or the 
distances of their two summits, a and y, from the base x z, 
which is done by measuring the two lines a h and c y, which 
must both be perpendicular to x z. To set out such perpendicu- 
lars for measurement, the surveyor's cross (Par. 230, Fig. 60) 
must be used. That instrument must be set upon the line and 
be moved backwards and forwards between x and z^ until two 
picket-rods fixed at the points x and z may be seen through one 
pair of sights, and another picket-rod at a may be seen through 
the other pair; and this can only take place when the instrument 
is fixed over the point 5, consequently a h must be perpendicular 
to X z, and a b will therefore be the line to be measured. That 
done, let it be supposed that it measures 5.50 chains. 

The cross must now be removed to another part of the line x 
z that shall be opposite to y, that is to the point c, in which the two 
picket-rods at x and z are visible through one pair of sights, while 
another rod fixed at y shall be visible through the other pair. 
This will mark the line c y as the other perpendicular to be 
measured; and suppose it to be equal to 6.30 chains, then the 
triangle x a z will be equivalent to 18.25x5.50 or 100.3750, and 
the triangle x y z io 18.25x6.30 or 114.9750, the sum of which 
is 215 square chains and 35 links. But in measuring triangles 
only half the product of the base by the altitude must be taken, 
(173,) therefore the half of 215.35, or 107.675, will be the cor- 
rect area of the piece of ground. 

We thus see that whenever a piece of ground can be reduced 
into triangles, whatever may be its primitive shape, its superficial 
quantity can be determined by one long and one short measure- 
ment in each triangle, without any notice being taken of the 
amount of the angles at the corners; and thus a very simple and 
easy, and at the same time correct, result is produced. 

235. The diagonal is of great use and importance in this prob- 
lem, because it is owing to its interposition that the measurement 
of the corner angles becomes unnecessary. Thus, for example, 
a piece of land abed, Fig, ^5, may be so nearly square at its 
corners and parallel in its sides that the unassisted eye might be 
unable to determine whether it was a regular parallelogram or 
not, and to decide this question it would be necessary to measure 



ON LAND SURVEYING. 113 

the two sides a b and c d, as well as « c and b d, to ascertain 
whether they were respectively equal to each other; and if that 
should be found to be the case, then the contents of the field 
could be obtained by multiplying a long side a c into a shorter 
one a b, or vice versa. Still, however, this field could not be 
plotted or drawn into a plan from these measurements, because 
we have no evidence that the angles a and c are right angles, or 
what their exact angular extent may be; and since the dotted line 
a /is equal to a b, and c e is equal to c d, these might be the true 
boundaries of the field, and might yield an equal result to calcu- 
lation. In order to determine the true shape of the figure, we 
must therefore measure the two angles at a and c by a theodolite, 
or other instrument for the purpose, and thus we have at least 
five operations to perform, viz: measuring the two angles at a 
and c, and the three lines a b, a c and c d, before the true form 
and proportions of the figure can be determined. But if the 
diagonal b c is introduced, then an equally exact determination 
of figure takes place upon measuring the diagonal b c, and the 
two perpendiculars a g and d h fall upon it from the points a 
and d; because, while the lines b c and a g retain a certain deter- 
mined length in respect to each other, and the distances c ^ or 
g b are given, it is impossible for the point a to change its posi- 
tion, or for the angle at a to vary. What is said of the triangle 
b a c equally applies to the opposite triangle b d c, and this may 
be considered as the basis of all the operations in ordinary land 
surveying. 

236. If the mere dimensions of land are alone required, no 
record need be made of the precise positions of the perpendiculars 
or ofisets a g or h d in the field book, as all that is required to 
be set down is the respective lengths of the three lines b c, a g 
and d h. But if a plan of the field has also to be made, then the 
exact distances c h, h g and g b upon the line b c must be noted 
down, as well as the lengths of the several lines or ofisets a g 
and d h; because all maps or plans are similar figures, and to 
produce them, all these lines must be laid down upon the paper, 
on a scale proportionate to the real lines upon the ground. 
Thus, if the diagonal line b c upon the ground is 60 chains long, 
then beginning at the point c, the first ofiset h d will be to the 
right or east, and will occur at 14 chains from c, as discovered by 
the cross, and this must be so noted in the book. The surveyor 
then walks along the line c by measuring it as he proceeds, and 
looking to the right and left to observe whether any house, tree, 
angle, or any other object occurs that has to be introduced into 
the plan. Thus, when he arrives at the 35th chain he will find 
himself opposite to the angle of a house at i, and this must be 
15 



114 ON LAND SURVEYING. 

again inserted in the book as a right hand offset at 35 chains. 
Again proceeding onwards, on arriving at ^ he will be opposite 
the angle a, which will be noted down as a left hand offset at the 
50th chain, (or 50th chain and any number of links, as the case 
may be,) after which the measurement is continued to h. That 
done, he returns along the line and measures the left hand offset 
from g to a, which is found to be 27 chains, and is noted in the 
book accordingly. He next takes the right hand oflfset from the 
diagonal to z, which fixes the position of the house, the dimen- 
sions of which must be separately taken in the margin of the book. 
Lastly, the right hand offset from A to ^ is measured, and may 
be 28 chains, which length is also put down. 

237. To produce the plan upon paper, the diagonal h c must 
first be laid down to any scale that will divide it into 60 equal 
parts or chains, and now the plotting scales [52) come into use. 
If a scale of 10 chains to an inch should be adopted, then the line 
b c must be 6 inches long, because the real line on the ground is 
60 chains. Taking off 14 chains on the scale with the compasses 
and transferring it from c to h, will give the point A, upon which 
the perpendicular h d must be erected by a pencil line. Taking 
35 chains from the scale and transferring it from c, the place of 
the offset i will be determined, and must be marked by a pencil 
line parallel to h d\ and in like manner the point g is determined 
at 50 chains, and a pencil line a g \^ drawn also parallel to h d^ 
or perpendicular to h c. The several lengths of the lines g_a, i 
and h d, are next determined by the scale and marked off, and 
this fixes the positions of the points a d and z, consequently 
drawing lines from a to b and c, and from ^to c and b, will com- 
plete the plan, all but putting in the house at i, which must be 
done to the same scale, from the dimensions previously taken and 
noted down. 

238. It has been stated that the points h and g, upon which 
the offsets or perpendiculars h d and g a are to be raised, must 
be discovered by the surveying cross; and this makes a few ob- 
servations on the method of using that instrument necessary, and 
they will apply equally to either of its forms shown at Figs. 60 
and 61. In measuring the piece of land just referred to, the 
surveyor's first operation would be to set out the diagonal line c b 
by means of picket-staves, and these are left standing until that 
line is done with. Instead of proceeding to measure it, his next 
attention must be to discover the first point of offset A, (presuming 
that he is proceeding from c towards Z>.) To effect this he walks 
along the line c b, taking the cross with him; and when he be- 
lieves himself opposite the picket-staff that has been previously 
set up at the angle d, he stops and plants his cross, by sticking 



ON LAND SURVEYING. 115 

the bottom of its staff into the ground, in the direction of the 
diagonal line just set out. He now turns one pair of the sights into 
the direction of this same line, and applying his eye to the instru- 
ment, looks towards h and c, and gets that pair of sights to range 
exactly with the line. That done, he leaves the instrument so fixed 
and looks through the other pair of sights for the stafi" at d; but to 
his disappointment he finds that he was mistaken in his position and 
has gone too far, for the sights direct him to the point tti instead 
of to d, and he must not turn the instrument round to catch the 
point d, for, if he did so, the other pair of sights would no longer 
coincide with the line c h. His labour is therefore thrown away, 
and nothing remains but to take up the instrument and walk back, 
say to 2, where he plants and adjusts it as before, and now finds 
that he has gone back too far, for the cross sights now direct his 
visual ray to n short of d. The instrument must therefore be 
taken up once more, and be re-set and adjusted perhaps three or 
four times before a perfect coincidence between the points h and 
c and one pair of sights is obtained, at the same time that the 
other pair of sights point directly to c?; and a repetition of this 
kind of adjustment must take place at every point upon which it 
is necessary to use the cross, however numerous they may be. 
This at once shows that the instrument is not one of very easy 
application; and in some instances it has been found so trying to 
the patience of the observer, that he will admit a small error in 
position, or will incline the stafi' of the instrument so that it no 
longer stands over the point in the ground which the bottom of 
the staff should indicate, and this cannot fail to introduce errors 
into the measurement that may amount to a link or more at each 
station. 

239. With the Reflecting Cross the case is very diflferent. It 
has no staff, but is carried in the hand, and requires no fixing 
or adjustment. The observer has only to w^alk along the line set 
out, applying the instrument occasionally to his eye, and looking 
at the mark h by direct vision through the unsilvered part of the 
looking-glass. As he proceeds he will see the picket-rod at d by 
reflection when he comes opposite to it, and then he stops, and 
releasing the small mill-wright's plumbet, Fig. 64, the string of 
which is passed through a small eye c?. Fig. 63, purposely fixed 
in the centre both of the top and bottom of the box, the point of 
that plumbet will indicate a precise spot upon the ground, which 
is the summit of the right angle required, and which is imme- 
diately marked by setting up a station staff, with a paper in its 
top slit, to indicate the point. He then walks on, and fixes and 
marks the other offset points; when, to prevent mistakes, all the 



116 ON LAND SURVEYIN<i. 

other picket-staves, except the two extreme ones on the points 
c and b, had better be taken up. 

240. The chain measurement now begins from the point c, 
and the number of chains and links that occur between the start- 
ing point and the first, and all succeeding offset points, being 
carefully noted down, the offsets themselves are next measured 
and set down; and should they be long, it will be advisable to 
bone them by picket-staves before the chain is applied. 

241. The best field book that can be kept for simple operations 
like that which has just been described, is to make an eye sketch 
of the form of the piece of land, and to set down the dimensions 
as they are taken upon such plan in their proper relative places. 
For more complicated operations a form of field book should be 
used which will be hereafter described. 

242. The mill-wright's plumbet or plumb-bob above referred 
to, and represented at Fig. 64, is a very useful implement to the 
Engineer for fixing machinery, and ascertaining any one spot 
that is directly over or under another. It is made of brass, with 
a sharp steel point at its lower side for indicating a precise spot. 
The whole should be turned in a lathe, and the suspending line 
enters the vertical axis of the instrument, so that the point can 
have no tendency to turn to one side or the other. 

243. The example that has been given of land measuring ap- 
plies to four-sided fields only; but even if they are more compli- 
cated, the same mode of operation would hold good. Thus Fig. 
52, Plate II., may represent the form of a piece of land bounded 
by seven right lined sides, and such a piece must be divided into 
five triangles by the four long diagonal lines shown by dotted 
lines m the figure. The short lines drawn perpendicularly to 
these diagonals show the offsets that must be taken to measure 
the five triangles separately, and the sum of their contents will 
give the contents of the entire piece of land. 

244. When the boundaries of fields are curves instead of right 
lines, the operation shown by Prob. XL., Par. 185, and Fig. 53, 

.must be resorted to. Thus, suppose a piece of land to be in the 
form shown by a b d efin Fig. 66, in which the side kbm c d 
is bounded by a crooked river, and the side a i k bhy 2i waving 
irregular fence. The boundaries of this field cannot be considered 
as straight lines, as in the preceding example, but the surveyor 
must consider how it may be divided so that the greater part of 
the land may be included in a small number of triangles. Ac- 
cordingly, by setting out the diagonals a d and a g, the portion 
included between (i d c is converted into one large and conve- 
nient triangle, and Ihat included between a g and f is reduced 
into another. Then by boning a line from a, so that it shall 



ON T.AND SURVEYING. 117 

just touch the projection /, it will lead to h, where a picket-staff 
must be erected, and another in contact with the river at c; and 
these will produce another large triangle a b c, and include all 
the land except the small irregular portions i k and m, and these 
must be obtained by Prob. XL. That is to say, the line a b 
must be measured by the chain and divided into any number of 
equal parts to be marked by stakes, and from each stake an offset 
must be measured at right angles to the line, and extending to 
the boundary. These short offset measurements are more con- 
veniently measured by a pair of offset staves than by the chain. 
The offset staves are light wooden rods divided into links, and 
each rod is 10 links, or 6 feet 7.2 inches long. They are made 
in pairs, because the mode of using them is to place the first rod 
upon the ground, with one of its ends in contact with the mark 
to be measured from. The next rod is then placed in contact 
with its end, and should the length require a third rod or more, 
that which was first laid down is taken up and moved to the end 
of the second, and so on. The sum of all the offsets so taken is 
then divided by their number, which will give the mean breadth 
of the irregular piece of land; and that mean breadth must then 
be multiplied into the length a b to obtain the superficial contents. 
The same operation must be performed upon the line b c to obtain 
the measurement of the small irregular portion ttz, between that 
line and the river. 

245. If the irregular boundary is but gently waving or undu- 
lating, a small number of offsets will be sufficient, and in that 
case it will be best to take them as nearly as can be estimated at 
the least, the greatest, and the mean widths that occur, as shown 
at J^ig. 53, where the line g is the maximum, e the minimum, 
and /"the mean width of the figure abed. If, on the contrary, 
the boundary is very irregular and uneven, a closer average width 
will be obtained by increasing the number of offsets in the same 
space. 

246. The process just described, it will be perceived, is that 
of taking offsets round an inscribed figure; but, in some cases, it 
may be necessary to adopt the opposite course, and take them 
within a circumscribed figure, that maybe generated for the pur- 
pose. Thus if the plan and dimensions of a lake or large pond of 
water d e/g, Fig. 67, should be required, it may be obtained by 
circumscribing it by the right angled triangle ab c. A trape- 
zium, or square, or parallelogram would do as well, but these 
figures could not be set out, because they would require the pre- 
vious formation of a measured diagonal and offsets, and that 
diagonal would pass across the water, and therefore could not 
be measured. The triangle is equally convenient, and has the 



lis ON LAND SURVKYTNG. 

advantage of all its lines being on dry land. To set it out, fix 
three picket-staves at the most projecting parts of the pond, as 
de and h. Then take the surveying cross and move it about 
until a point a is discovered, from which the staves 3it d e will 
make a right angle with that at h, when the two lines a de b and 
a h c, may be set out and indefinitely continued by additional 
picket-rods. The right angle bacwlW now be established. Then 
place picket-rods on the most projecting points y and ^, of the 
other side of the lake, and select a point b or c, upon one of the 
two lines previously set out, at which the two rods /"and g will 
bone, or appear in a right line. That done, the line be may be 
set out, and the point b in the line a b, as well as the point c in 
a e, will both become fixed, when the lines a b and a e, are to be 
separately measured by the chain, and the area of the whole tri- 
angle b a e determined, in which there will be no difficulty, since 
it is equal to half the product of two of its sides into each other. 
To determine what must be deducted from this quantity on account 
of the lake being less than the triangle, internal ofi^sets must be 
made from each side of the triangle to the water, as in the last 
case, or triangles may be cut ofi'from the corners, provided they 
are too large to admit of offsets; and, in this manner, the quan- 
tity of deduction may be ascertained with considerable accuracy. 
247. It sometimes facilitates the operations of land measuring, 
to change figures or areas of one form, into others of a simpler 
character, but which shall retain the same dimensions; and on 
this account the few problems, which follow, may occasionally 
prove useful. 

Problem LIX. 

248. To eonvert a parallelogram into a square of equal area. 

Rule. — Multiply the length of the parallelogram by its breadth, 
and the square root of the product will be equal to the length of 
one side of that square, which is equal to the parallelogram.* 

Problem LX. 

249. To reduce a rhombus or rhomboid to an equivalent 

square. 

Rule. — Multiply the base by the perpendicular height from 

* Those who possess tables of logarithms, will find the labour of extracting 
square roots much abridged by their use, for the operation is performed by di- 
viding the logarithm of the power by its index, when the quotient will be the 
logarithm of the root; consequently half the number that expresses the logarithm 
of any number, will be the logarithm of its square root, the natural number 
corresponding to which must be found in the tables. 



ON LAND SURVEYING. 119 

one side to that opposite to it, and the square root of the product 
will give the side of the square required, as in the last case. 

Problem LXI. 

250. To reduce a trapezium to a square of equal area. 

Rule. — Multiply its diagonal by half the two perpendiculars 
or offsets raised upon it, and the product will be thea rea; con- 
sequently the square root of that area will be one side of the 
square required; because the side of the square is a geometrical 
mean, between the diagonal and the half sum of the perpen- 
diculars. 

Problem LXII. 

251. To reduce a trapezium to a triangle of equal area. 

Let ahc d. Fig. 68, be the given trapezium. Draw the diago- 
nal a c, and extend the base line a d towards e; draw b e parallel 
to the diagonal a c, and from the intersection at e, draw the line 
e c, which will complete a triangle e c d, equal to the trapezium. 

Problem LXIII. 
252. To reduce an irregular pentagon to a triangle. 

Let a b c d e, Fig. 69, be the given figure. Divide it into three 
triangles by drawing the two diagonals a c and e c, from the point 
c; and prolong the base a e towards^ and/! From the point b, 
draw b g parallel to a c; and from the point d, draw df parallel 
to c e, which will give two fixed points^ and/; from these draw 
g c and cf forming the triangle g cf, which will be equal to the 
given pentagon. 

253. The plane table, before referred to, is a simple instru- 
ment, which produces the map or plan at the same time that the 
survey is made, and being easily used, the Engineer and Land 
Surveyor frequently avail themselves of it for simple surveys, 
notwithstanding it requires more measurements to be taken upon 
the ground than the method of triangulation, which has been 
before described. It is merely a rectangular flat board, or rather 
a pannel drawing-board (23) of at least fifteen by twelve inches, 
the frame of which not only serves to retain the sheet of paper to 
be drawn upon in its place, but it is graduated on its upper sur- 
face into angular degrees, radiating from the centre of the board. 
The general appearance of the instrument is shown at Fig. 70, 
Plate II., in which abed represents the drawing-board with its 
angularly graduated border, supported upon an ordinary tripod 
stand of the kind generally used with surveying instruments, 



120 ON LAND SURVEYING. 

parts of the legs of which are shown diifff, and by these it is 
elevated to about four feet from the ground. These legs are 
jointed together at their upper ends, so that by extending one leg 
more or less than the others, the drawing-table may be made 
level; or sometimes a ball and socket-joint intervenes between the 
top of the legs and bottom of the plain table, for producing this 
adjustment to level. A wooden magnetic compass-box e, is made 
to slide into a dovetail on one side of the table, for taking bear- 
ings by its magnetic needle; but the top of this compass must be 
kept below the upper surface of the table, in order that it may 
not impede the free motion of a flat brass ruler m ?7^, which lies 
upon the table, and has a vertical sight plate g g upon each of its 
ends, which are pieces with apertures, like those of the survey- 
ing cross. Fig. 60. This brass ruler and sights is not attached to 
the table, but is free to move in any direction; and a series of 
chain or decimal scales are, generally, engraved upon its upper 
surface. A small brass plate is let into the centre of the table, 
flush with its surface, and this has a small hole in it, just large 
enough to admit a small common pin h; and another plate with 
a similar hole for a pin is let in at i, close to the edge of the 
drawing-board, so that a pin may be placed in either of these 
holes, by passing it through the paper, when the instrument is in 
use. 

254. The plane table may be used either in the middle, or 
boundary of the estate to be surveyed, and depends upon the 
principles of similar figures in geometry. Thus suppose k, /, m, 
n, o, Fig. 71, to represent a five-sided field that has to be sur- 
veyed, and that a plane table, covered with paj^er, and represent- 
ed by the small square p q r s, is fixed near the middle of the 
field. Picket-staves, or other objects must be set up at each an- 
gle of the field, and a pin is inserted in the hole, in the middle of 
the table. The ruler and sights is now to be placed upon the 
table with its fiducial or chamfered edge in contact with the pin, 
and while in this position it is to be turned round until the object 
at ^ is seen through the sights, when a pencil line^ t is drawn 
upon the paper. That done, the sight ruler is turned until the 
object at /, is seen as before; it is next turned into the direction 
t 771, and so on, (being constantly kept in contact with the pin,) 
until it has been presented to every object around the field, when 
a series of lines will be obtained upon the paper, all radiating 
from the centre /, and pointing to the several angles around the 
field. That done, a plumbet is dropped from the under side of 
the centre of the table, and a stake fixed where it touches the 
ground, when the several distances from that stake to the angles 
k 1 77171 and o, must be measured by the chain, and these lengths 



ON LAND SURVEYING. ' 121 

must then be transferred by the compasses and one of the scales 
upon the ruler to the paper, making each measurement to proceed 
from the centre of the table, upon the lines to which they respec- 
tively belong, and marking their extreme points. Lines are now 
ruled from one of these points to the other, when such lines will 
be parallel to the boundaries of the real field, and the small figure 
thus produced upon the paper, will be similar and proportionate 
to the field itself, as indicated by the small similar figure drawn 
within the table jO q r s. 

255. In the example given in the figure, the lines t o, t k, and 
t I are all equal, as indicated by their being radii of the arcs drawn 
round the figure from its centre t; but t m and t n are shorter, 
and do not reach the arcs. 

25Q. Fig. 12, gives an example of the manner of using the 
plane table in the boundary of a field, in which case it must be 
placed in one of the angles of that boundary as at v, (pqrs still 
representing the plane table.) The pin must now be placed in 
the hole i, Fig. 70, near the edge of the table, which is used as 
before; for sights are taken and lines drawn in the direction of 
every angle of the field, as indicated by the lines in the figure, 
and each of these lines has to be measured upon the ground and 
transferred by scale and compasses to the plan, as before. 

257. When the plane table is used as last described, the an- 
gles of sight cannot be given by the graduated border unless, as 
is sometimes the case, this border is so fitted as to admit of it 
being reversed, and another division into angles from the side 
pin, is engraved upon it. The use of these angles is to obtain 
the measure of the field, which the plane table divides into a se- 
ries of triangles, of which the two sides, with their included an- 
gle, are given, and from this the contents may be obtained. But 
as the process is more troublesome than by the simple process of 
triangulation before described, the plane table is not so much re- 
sorted to for obtaining the contents of land, as for producing a 
plan or delineation of its form and proportions, and if these are 
correctly drawn to a large scale, the contents may be obtained by 
scale and construction upon the plan, with tolerable accuracy and 
expedition. Some persons do not use the pin at all, but make a 
dot upon the paper, to which the ruler is applied. 

25h>. If more extensive surveys have to be made, the processes 
that have been described will not accomplish them, but other 
means, and more expensive instruments, must be resorted to; for 
now the angles that occur between one visible object and another 
must be measured with great accuracy by means of a circumfe- 
rentor, or theodolite, and the observations so made have to be 
recorded in a field book, by as short a process of entry as possible; 
16 



122 ON LAND SURVEYING. 

but at the same time such a one as will be intelligible at a future 
time for making out the map or plan in the office. 

259. The circumferentor in its usual form is shown at Fig. 
73, Plate II. It consists of a flat bar of brass, about fifteen inches 
in length, marked a a, with sights b c, at its opposite ends, and 
in the middle of the bar is a circular brass box d covered with 
glass, and containing a magnetic compass needle. The ends of 
the needle play very near to a brass circle, divided into 360 equal 
parts or degrees, by two semicircles of 180° each^ such divisions 
commencing upon the line that unites the two sights, so that the 
two numbers, 90°, are at right angles to a line drawn through the 
sights. Each sight has a very narrow slit to look through, and 
a large opening with a fine wire or horse's hair strained across it; 
and these are placed alternately, or with the slit uppermost and 
large opening below in b, and the large opening above, and slit 
beneath it in c, so that the instrument can be looked through with 
equal advantage in either direction. It is supported at a conve- 
nient height, for looking through, upon a single pointed staflf, or 
common tripod stand, either of which must pass into the socket d^ 
which has a screw z, for fixing the instrument firmly to it, but 
it can be turned round and adjusted to a level position by a ball 
and socket-joint e, without which the compass needle would not 
traverse or move freely round. 

260. A well balanced magnetic compass-needle moving freely 
in a horizontal position upon the sharp point by which it is sus- 
pended, has the property of always pointing to the north, with 
the exception of a certain small angular deviation, called the va- 
riation of the compass; and as this quantity of variation is known, 
or can at any time be ascertained, it may be considered as of no 
importance, because it can always be allowed for. This allow- 
ance must be made, so as to make the magnetic agree with the 
true meridian; because it is not general or alike in all countries, 
and it is also subject to a progressive change, but at so slow a rate 
as not to afiect ordinary operations. The circumferentor may, 
therefore, be turned round until the needle stands parallel to the 
long bar a a, when its two ends will correspond with the north 
and south points, engraved on the inside of the comjDass-box, and 
will point to the cipher and 180°, among the divisions. If now 
the bar and sights be turned into a new direction, the needle will 
not move, but will remain pointing in its former north and south 
line; consequently its new position among the divisions, compared 
with its former one, will give the measure of the angular quantity 
that the instrument has been turned. 

261. The degree of perfection with which the circumferentor 
can measure an angle depends, therefore, entirely upon the good- 



ON LAND SURVEYING. 123 

ness and length of its magnetic needle. If that is short, the di- 
visions on the circle will be proportionately small; and if there 
is friction on the central pivot, the needle will not move freely, 
or always settle in the same place, but will follow the motion of 
the instrument in turning it round, to such a distance, as frequent- 
ly to make a difference of a degree or two in the result, which is 
not, consequently, always to be relied upon. To remove these 
defects the needle should be from four to five inches long; should 
be strongly magnetized, but made as light as possible. If it is 
longer, or contains too much steel, it will be too heavy to vibrate 
freely. The point on which it turns should be very acute and 
sharp, and be made of well hardened steel, and the cap of the 
needle should be of agate, rock crystal, or some hard stone. The 
compass should have a lever or stop, to lift the needle off the 
point whenever the instrument is conveyed from one place to 
another; otherwise the shaking of the needle against the point, 
will soon cause it to become blunt; and whenever the instrument 
is used to take an observation, and has stood still long enough for 
the needle to become stationary, the compass-box should be gent- 
ly tapped with the fingers, before the position of the needle is read 
off, as the vibratory motion, thus communicated to it, will gene- 
rally cause it to move through a small arc into its proper place. 
On account of these imperfections the circumferentor is not much 
used in England, or where land is very valuable; but it is much 
used in America, and is a convenient and expeditious instrument, 
where, on account of woods or other impediments, the sights are 
short, and great accuracy is not required. In the largest and best 
instruments the degrees are divided into halves, but it requires 
an excellent needle, and very careful use and observation, to per- 
mit reading off to this degree of precision. An improvement 
has been made in the construction of this instrument, which will 
be better understood when the theodolite has been described. 

262. The instrument most to be relied upon for accuracy, and 
which is constantly used in all correct surveys, is the Theodolite. 
It is made wholly of metal in various forms, but that which is 
most compact and convenient is shown at Fig. 74, Plate II. 
The principal difference betw^een the theodolite and the circum- 
ferentor is, that this latter instrument, when moved or turned, 
all turns together, with the exception of the compass-needle, 
which ought to stand still; but no evidence is given of its having 
done so, because the division or figure to which its end pointed 
has been moved away from it, and perfect confidence must there- 
fore be placed on the goodness of the needle. The theodolite, 
on the contrary, is always composed of two, and, in the best in- 
struments, of three distinct parts, which have separate move- 



124 ON LAND SURVEYING. 

ments, by the two first of which, the original direction and object, 
and the new object, together with the angle it makes with the first 
direction, are maintained and may be re-examined; while the 
third motion is for the purpose of measuring vertical angles, or 
angles in a plane that is perpendicular to that in which the first 
angle was taken. The theodolite, therefore, does not depend 
upon the compass-needle, but upon its own separate parts for the 
measurement of angles; and although a compass always forms a 
component part of the instrument, yet it is only added for giving 
the bearing of the measurements as they are taken. 

263. Theodolites, as formerly made, were only capable of 
measuring angles in any one plane, and they consisted of a whole 
or half circle of about 10 inches diameter, divided into the proper 
number of degrees, viz: 360° for the entire circle, or 180° if they 
were semicircular. This divided plate was mounted on a tripod 
stand, so as to stand in a horizontal position, and it had two plain 
slit and horse-hair sights, just like those of the circumferentor, 
(254,) rising from its opposite sides so as to guide the sight in 
the direction of a diameter; such sights being placed opposite to 
the divisions marked 0° and 180°. Another piece, formed in 
every respect like a complete circumferentor, if deprived of its 
stand and ball and socket, was attached by a pivot to the upper 
side of the brass plate, in such manner that it would move quite 
round upon it, by being made short enough to pass clear of the 
external sights. The four sights could by this construction be 
brought into a right line; and as the holes in them were made to 
correspond, a right lined sight could be taken through the whole 
of them at once, or the two exterior sights could be placed in the 
direction of one object, while the internal pair were directed to 
another; and thus the angle subtended by the two objects at the 
centre of the instrument could be ascertained, because the end of 
the shifting bar that carried the inner sights had an index that 
pointed to the divisions upon the graduated circle, and the com- 
pass in the centre of this piece indicated the bearings of the lines 
forming such angle. A joint was formed in the stand of the in- 
strument, by which its plate could be thrown from its horizontal 
into a vertical position whenever it became necessary to measure 
vertical angles, but no angle could be measured out of the plane 
in which the instrument was placed. 

264. Two great improvements have been made in instruments 
for measuring angles on the ground. The first arising out of 
Ramsden's invention of dividing angular instruments by ma- 
chinery, in consequence of which such accuracy is obtained that 
much more perfect observations can be made w^th instruments 
having circles of only 4 inches diameter, than could formerly be 



ON LAND SURVEYING. 125 

produced by those of 10 inches, or even a foot. It formerly 
required a large instrument and perfect observer to measure an 
angle in surveying to the tenth of a degree, while now an instru- 
ment is scarcely ever offered for sale that will not measure angles 
to minutes or the 60th part of a degree, though their circles may 
not be more than three inches diameter. 

265. The second improvement is in the adoption of a small 
telescope attached to the instrument for observing, instead of the 
slit and horse-hair sights formerly used. The horse-hair, from 
its proximity to the eye, subtends so. large an angle as to be 
capable of covering a tree or any distant object as much as a foot 
or more in diameter; and this, added to the indistinctness of dis- 
tant objects, renders it impossible to take a sight with any toler- 
able precision. But when a telescope, even of small power, is 
used, it defines distant objects so clearly that a sight may be taken 
to within half an inch. The hair used for marking the position 
of the object is placed at the focus of the eye-glass of the telescope 
within its tube; and being thus magnified and protected from ex- 
ternal injury, it may be made much finer than in the other case, 
so that a single fibre of silkworms' silk, or even a filiment of 
spiders' web thread, is frequently made use of, and the greatest 
precision is obtained. In order to obtain the greatest magnifying 
power with the least length of telescope, the inconvenience of 
apparent inversion of the object looked at is generally submitted 
to in the telescopes applied to surveying instruments; but this 
does not afiect the angle or apparent position of the object, and 
ceases to be an inconvenience w^hen the operator has become 
accustomed to it. As the theodolite is applied to measuring 
vertical as well as horizontal angles, two hairs which cross each 
other at right angles are always applied to the telescope; and to 
take a sight with precision, the telescope is moved horizontally 
and vertically until the intersection of the hairs exactly covers 
the point intended to be measured from, so that if the telescope 
inverts and is directed to the vane upon a distant church, the 
appearance on applying the eye to the telescope will be such as 
is shown at Fig. 74, Plate II. 

266. The divisions of a circle into degrees could not be carried 
to the extent that has been spoken of unless the circle is very 
large, or they would become so small as to be invisible, besides 
being very expensive in their construction on account of their 
number, and the exactitude necessary in laying them down. On 
all these accounts circles are never so divided, but a most elegant 
contrivance called a Vernier (from the name of its inventor) is 
adopted, and by its means, if well executed, the divisions upon 
instruments may be carried to any degree of minuteness required. 



126 ON LAND SURVEYING. 

This contrivance has now become so common in all good instru- 
ments for accurate measurements, that a perfect acquaintance 
with its principles, which are very simple, is necessary. Sup- 
pose, for example, it is required to divide inches into hundredth 
parts, as in the common. barometer. The scale of inches is en- 
graved in the usual manner, and each inch is divided into 10 
equal parts, as in Fig. 75, Plate II. The vernier is a thin plate 
of metal v v, applied in such manner as that it may slide freely, 
or free from jerks, against the line of divisions, but with sufficient 
friction to remain in anyplace where it maybe fixed. The side 
of the vernier next to the divisions has a fiducial edge, which is 
made to coincide with them as closely as possible, and upon this 
an index, oy fleur de lis^ and another set of divisions are engraved, 
as numbered 1, 2, 3, &c., to 10. The index denotes the point 
to be counted from, and the divisions are obtained in the follow- 
ing manner. Below the index a space is set off by compasses, 
equal in length to eleven of the divisions upon the scale of inches, 
and this space is then divided and marked off into 10 equal spaces, 
as indicated by the numbers. Of course, therefore, each division 
upon the vernier must be one-tenth longer than the divisions 
upon the scale; for if the index is set against any division. No. 10 
upon the vernier will stand opposite the eleventh division below 
the index upon the scale of inches, and thus the vernier scale is 
capable of subdividing each of the smallest divisions upon the 
principal scale into 10 equal parts; and as the smallest divisions 
upon the principal scale are tenths of an inch, the vernier will of 
course read off to hundredths of an inch. To use this scale, ob- 
serve where the index points to on the principal scale. If it 
coincides exactly with any division, then that division shows at 
once the quantity measured. But if it stands between two divi- 
sions, as in the figure, where it is made to point between the 
fourth and fifth division above 29, then look down the vernier 
for the first actual coincidence of lines that occurs, and that will 
be found at No. 4 on the vernier, for 3 is a little above, and 5 a 
little below its opposite division. Four, or four-tenths of the 
tenth of an inch, is therefore the quantity indicated by the ver- 
nier as it stands in the figure, and this quantity would be read 
29 inches and four-tenths of an inch; which, expressed decimally, 
would be equivalent to 29 inches 44 hundredths. If the index 
had corresponded exactly with a division, then no coincidence 
would be found between the divisions on the scale and those on 
the vernier, except No. 10; and as ten-tenths make a vrhole, that 
would indicate that no fraction existed, but that the division to 
which the index pointed must be taken as a whole number. 
267. The vernier is applied in a similar manner to the subdi- 



ON LAND SURVEYING. 127 

vision of the graduations upon divided circles, with this difference 
only, that in the barometer the scale is stationary and the vernier 
is moved to it, but in divided circles the vernier is fixed and the 
circle moves in contact with it. Reflecting quadrants and sex- 
tants are exceptions, because in them the vernier is attached to 
the index, which is moved, while the divided limb remains sta- 
tionary. The principle is, however, the same in all cases, and 
depends upon the divisions on the vernier being greater in a cer- 
tain known proportion than they are in the scale it is used to 
divide. Thus Fig. 76, Plate II., may serve as an example of 
the manner in which a vernier v v may be applied to subdivide 
the degrees upon w w, which may be supposed to represent a 
portion of the divided circle of a theodolite, or other instrument 
intended to measure angles to single minutes of a degree. The 
vernier in this case is supposed to be stationary by being attached 
to some fixed part of the instrument, while the circle of which 
w w is a. part revolves on its proper centre, keeping its divisions 
in contact with those of the vernier. In these cases, as the divi- 
sions are small in minute instruments, they are read, and the 
coincidence is observed by a magnifying glass or microscope, 
which is commonly attached to the instrument for the purpose. 
The circle is divided into degrees, or 360 equal parts, and for the 
facility of distinguishing the degrees or reading off, as it is called, 
every lOLh degree is marked with a number, as 0, 10, 20, &c., 
and the intermediate degrees which extend over three of the 
concentric circles round the edge of the plate have to be counted. 
Each degree, it will be observed, is divided by shorter lines ex- 
tending between the two outer circles into three equal parts; and 
as the whole degree contains 60 minutes, so of course each of 
these small divisions are equivalent to the third of a degree, or 

20 minutes. All the vernier, therefore, has to do, is to divide 
each of these small spaces into 20 equal parts of 1 minute each; 
and to effect this, the divisions on the vernier must extend over 

21 divisions upon the circle, and have this extension divided into 
only 20 equal parts, which are numbered 5, 10, 15, 20, from the 
index, as will be seen in the figure. The vernier is used as be- 
fore directed, the index on the vernier pointing to the division 
on the circle, which is to be taken as the measure of the angle 
under examination. Thus, in the figure it points above the 8th 
degree, and looking for the coincident lines they will be found 
against 10 on the vernier, which indicates 8° 10', because the 
index points short off from the first short or 20 minute division. 
Had it been in the same position, but above that division, then 
the reading would have been 8° 30', because the first 20 minute 
division would then be taken into account. 



128 ON LAND SURVEYING. 

268. Verniers are not always divided as above described, but 
are various in their forms; but as the principle remains un- 
changed, a little consideration will enable any one to judge of 
the subdivision they produce. Thus the degrees on the circle 
sometimes are entire, or not divided into thirds or even halves, 
and the vernier may contain 12 divisions, in which case the 
whole degree is only divided into 12 parts, and consequently 
each division on the vernier will be equivalent to, and will 
divide the degree only to every 5 minutes, 5 times 12 making 
60. A very common mode of division on small instruments, is to 
divide each degree into halves, and to have a long vernier with 
thirty divisions upon it, and this will give the thirtieth of half a 
degree or single minutes, as in the first process. A similar length 
of vernier, with double the number of divisions upon it, will di- 
vide to half minutes or thirty seconds. On the best and finest 
astronomical instruments this process of division is often carried 
to ten, five, three, and even single seconds, but such nicety is 
never required for the ordinary purposes of surveying. Even 
when an instrument reads to single minutes, it requires delicate 
screw or rack-work motions for its adjustment to objects, because 
it cannot be moved by the hand with sufficient delicacy. 

269. Having thus pointed out the nature of the improvements 
that have been made on the instruments for measuring angles, no 
difficulty will occur in comprehending the parts of the improved 
theodolite, as represented by Fig. 11 of Plate II., a ^ is a tele- 
scope about twelve inches long. The small tube at the eye end 
«, slides in and out for adjusting the cross hairs, {Fig. 47,) to a 
proper focus, and the object-glass end h, slides in a similar man- 
ner for adjusting the focus of the telescope to distant objects. The 
cross hairs are adjusted into their position by small screws at c. 
The telescope is not attached to the instrument, but rests in two 
forks (Id, called Y's, from their similarity in shape to that letter, 
and a spring cap folds over each Y to hold the telescope in its 
position. The Y's are fixed upon the upper part of a brass semi- 
circle e e, which is supported on its proper centre by a double 
conical axis/yj resting and turning on points^, in the tops of the 
angular shaped supports A A A A, which are fixed upon the hori- 
zontal plate k k. The semicircle e e is divided into degrees on 
one of its sides, which are read off by a vernier, attached to a 
block /, immovably fixed upon the horizontal plate, and is for 
taking vertical angles; the other side is divided, in a manner to be 
hereafter described, for reducing hypotenusal lines to horizontal 
ones. This semicircle has teeth on its outer edge, which are acted 
into by a pinion, concealed within the block /, and turned by the 
wire and milled nut rriy by which alone the telescope should be 



ON LAND SURVEYING. 129 

moved in its vertical direction. A magnetic compass is fixed in 
the centre of tlie horizontal plate at n^ and o, o are two spirit- 
levels,* also fixed upon it at right angles to each other, by means 
of which, this plate can be set truly level or parallel to the hori- 
zon, without which precaution the circle e e and telescope, could 
not be used for taking vertical angles. As a further precaution 
to insure accuracy in this operation, as well as for other purposes, 
another spirit level w is fixed by screws to the underside of the 
telescope, and rendered parallel to its axis, or line of collimation. 
When the horizontal plate is made quite level, and the or zero 
point of the semicircle stands against the index of its vernier 
upon /, the level w, with its telescope, ought likewise to be quite 
level, which is a proof that this part of the instrument is in per- 
fect adjustment. 

The horizontal plate A: A: is chamfered or bevelled on its exter- 
nal edge, so as to become a portion of a cone, and appears solid 
and of considerable thickness; but it in fact consists of two 
parallel plates made to fit so closely together that no space ap- 
pears between them, and the division of the lower plate into de- 
grees takes place at this juncture; the degrees, with the figures 
for counting them, being wholly engraved on the lower plate q q, 
and nothing on the upper one except the verniers, for reading the 
divisions; and a similar vernier is placed on the further side of 
the top plate exactly opposite to the first, which gives the great 
advantage of reading off the divisions in two places, and taking a 
mean of them, in case of error. In the best and most costly in- 
struments, this bevelled edge of the bottom plates, and the divided 
arcs upon the semicircle, as well as their verniers, are made of 
silver or platinum, which admits of the figures and divisions 
being more finely engraved, and more easily read, and when the 
latter metal is used, never tarnishes. The upper plate k k re- 
volves on the lower one q q, upon a central long arbor, which 
should be of the finest workmanship, and descends some distance 
into the stemjt? of the instrument; and motion is given to this upper 
plate by another concealed pinion, connected with the milled head 
r, which acts into teeth also concealed, but which are cut upon 
the lower interior part of the plate k k. 

Two brass plates, s and v, called the parallel plates, are con- 
nected together by a ball and socket, or conical piece f, in such 
manner that they are at liberty to move out of their parallel po- 
sitions, but cannot separate beyond certain limits; and four strong 

* For an explanation of the construction, use, and importance of spirit-levels, 
see the next chapter, where the method of adjusting this instrument is also de- 
scribed. 

17 



130 ON LAND SURVEYING. 

screws, with milled heads x xxx, are placed in two diameters, 
and work through the top plate, while they merely press against 
the bottom one, so that by tightening these screws, the two 
plates are fixed at their greatest possible distance apart, and 
the upper plate may be made exactly parallel to the lower one, 
or be placed in any small angular position in respect to it; or if 
the under plate is out of level, the upper one may be made quite 
level. The three folding wooden staves or legs, which form the 
stand of the instrument, and raise it to its proper height for ob- 
servation, are attached to the under side of the lower plate v^ and 
the theodolite, or any other instrument, is fixed upon the upper 
plate by a pivot that enters the socket jo, and is fixed by a thumb 
screw. 

270. A separate tripod or three legged folding stand is always 
sold with each theodolite or other surveying instrument; but it 
seldom happens that the pivot-socket at jt?, by which the instru- 
ment is attached to its stand, will fit any other instrument than 
its own, from wliich practical difficulty sometimes arises in the 
operations of the Engineer. It is, therefore, much better to have 
all his instruments fitted to one stand, or to have two stands 
which fit all his instruments in common. This is not only con- 
venient but economical, for a well made stand is worth from se- 
ven to ten dollars, and the expense of an instrument is so much 
diminished in its cost. The legs are often made to unscrew in 
the middle, to render them shorter and more portable on journeys. 

271. The several parts of the theodolite having been examined, 
a few words of explanation may be necessary as to the mode of 
using it. The legs y y y oi the stand are opened to a sufficient 
extent to insure the steadiness of the instrument; and they ought 
to be set on hard ground, or pushed into that which is soft, until 
the stand is firm and steady. In placing the stand, attention 
should be paid to getting the under parallel plate t>, as level as 
possible, which may always be effiscted by spreading out one or 
other of the legs, until the level position is attained b}^- estimation. 
The bottom plates k q of the theodolite are then to be brought 
into a perfectly level position by means of the levelling screws 
X X X X, which position is determined by the cross spirit-levels 
upon the top plate k k, and proved by turning that plate quite 
round, when the bubbles of the levels should remain motionless. 
The index of the vernier upon k must then be brought to coin- 
cide exactly with the or point from which the divisions com- 
mence on the bottom plate q q, and that done, the two plates are 
clamped or fixed together by a screw opposite to r, but which 
cannot be seen in the figure, so that one plate cannot move with- 
out the other. That done, the telescope is directed to the first 



ON LAND SURVEYING. 131 

object to be observed, by turning the whole instrument round 
upon the pivot at j», while the telescope may be raised or de- 
pressed at pleasure by the nut m^ since in taking a horizontal 
angle, the elevation of the telescope will not affect it, because 
however the telescope may be placed it cannot turn to one side 
or the other, being restrained from doing so by its long axis/y", 
and supporters h h. The first object being brought correctly to 
the intersection of the hairs, the instrument is immovably clamp- 
ed by a thumb screw that enters the side oi p. The top plate 
kk'is now undamped and moved by its nut r, until the telescope 
is brought to bear upon the second object to be observed, when 
the angle subtended between the two objects may be read off at 
the vernier s. Should any doubt exist respecting the correctness 
of the observation, the telescope may be turned back again to the 
former object, to ascertain whether the vernier will again stand 
at when that object is again seen. In the very best theodolites 
there is a telescope with cross hairs, fixed under the lower plate 
q q, in the direction of its zero point, and which remains con- 
stantly fixed upon the first object for the purpose of verification. 
It is thus seen that an angle is taken without any reference 
to the compass n, which is used merely for giving the bearing of 
the lines that form the angle should it be required. 

272. When speaking of the circumferentor, (261) it was stated 
that an improvement had been made in that instrument which 
would be noticed after the theodolite had been described. 
That improvement consists in converting it, to a certain extent, 
into a theodolite, by leaving out the ball and socket e, Fig. 73, 
in which case the instrument must be used upon a stand with 
parallel levelling plates (like that in Fig. 77) for the purpose of 
levelling it. Instead, therefore, of turning round upon the ball 
and socket, it turns upon the conical pivot of the stand which 
enters the socket d, and may be firmly fixed in any position by 
the screw of that socket. The compass-box is united to the up- 
right stem e d, which passes through the bar a a, and this bar 
is moveable round the compass upon the stem e d as a. centre, 
but can be locked or fixed to it at pleasure, by a tightening 
screw under the instrument, so that one cannot move without 
the other. The lower outside rim of the compass-box is regu- 
larly chamfered, and divided into degrees, and a vernier, or 
two opposite ones are placed on the bar at y y for reading these 
divisions. A wheel and pinion or tangent screw is, moreover, 
applied underneath for moving the arm and sights very gradually 
round the compass, and when so equipped the circumferentor 
becomes nearly as efficient as the theodolite. 

273. As an example of the mode of using it (and which will 



132 ON LAND SURVEYING. 

apply equally well to a theodolite,) suppose abed efg, Fig. 
78, Plate II. to be the boundary of a piece of land to be sur- 
veyed, and let the parallel lines NS., NS., &c., ruled through 
every angle of the same, represent so many parallels to the mag- 
netic meridian, or the direction in which the compass-needle 
will point whenever it may happen to be placed upon the estate. 
Begin by placing the circumferentor at the angle «, level it, and 
having brought the north and south parts of the compass-box to 
coincide exactl}^ with the line of the sights, which is done by 
bringing the 0° on the bottom of the outside of the compass-box 
to the index of the vernier, lock the compass and bar together: 
now turn the whole instrument on its socket d until the needle 
stands directly over the north and south line of the compass-box, 
when the sights will stand in the direction a N upon the 
plan. The instrument must now be locked or fixed in this po- 
sition by tightening the socket-screw z. The compass must 
then be unlocked from the bar, and the bar with its sights turn- 
ed into the direction a b, (a picket-staff having been previously 
set up at b, as well as at all the other angles) when the angle of 
deviation will be noted, not only by the vernier y, but by the 
needle also, in the improved instrument, or by the needle only, 
in the common one. This angle suppose 7° 00', must now be 
set down in the field book, but before doing this, if w^orking 
with the improved instrument, observe that the needle still stands 
over the north and south line, or that the compass-box has not 
shifted its place. While this angle is measuring, the chain-bear- 
ers proceed from* the point a to measure the length of the line 
from a to b, and there they remain, leaving the last chain upon 
the ground until the surveyor comes up with his instrument, 
counts their arrows or markers, and the odd links to the point b, 
which suppose may be 31 chains 10 links, and this he now 
enters in his book, and sends them to measure the next line 
from b to e; while he again adjusts the instrument now placed at 
b, for the purpose of ascertaining what angle the line b c makes 
with the magnetic meridian NS, or in other w^ords, while he 
measures the angle N b c, which is done and entered in his 
book as before, suppose it to be 55° 15' E. He then proceeds 
to c, where he obtains the length of the line b e from, the chain- 
bearers and enters it, suppose 28.21 chains. They then proceed 
to measure from c to d, while he takes his station at e, and having 
adjusted his instrument measures the angle S c d and enters it 
S. 12.40 E. In this manner he proceeds to each corner of the 
estate until he arrives at g, when the next sight carries him to a, 
the point from which he started, and the entries he will have 
made in his field book will be as follows: 



ON LAND SURVEYING. 133 



chains. 

7? 

?? 
7? 



1. 


AtoB 


North 


7° 00' 


West 


31.10 


2. 


B to C 


North 


55° 15' 


East 


28.21 


3. 


C toD 


South 


62° 30' 


East 


24.41 


4. 


D toE 


South 


40° 00' 


West 


21.00 


5. 


E to F 


South 


4° 15' 


East 


24.00 


6. 


F toCr 


North 


73° 45' 


West 


22.40 


7. 


G to A 


South 


52° 00' 


West 


19.18 



In the above entries the columns in which nothing but the 
words north and south occur, is a register of the end of the 
needle that has been made use of in making the observation, and 
the column of east and west shows whether the angle is taken 
on the east or west side of that end of the needle. As a general 
rule, that end of the needle is selected which makes an acute 
angle or one of less than 90° with the line observed. The entry 
in the field book north 7° 00' west, means that the angle measured 
is 7° to the westward or left hand side of north, as shown by the 
needle. By north 55° 15' to the east, is meant to the east or 
right hand side of the needle. By south 62° 30' east, is meant 
that quantity to the eastward or left hand of the south end of the 
needle. And by south 40° west is 40 degrees to the westward, 
or right hand of the needle's south end. In applying the terms 
right and left hand it must be understood that the face of the 
observer is turned towards that end of the needle he is using 
while he himself is supposed to be over the centre of the needle. 
And following this rule while referring to the plan I^ig. 78, it 
will be found that the angles measured in succession and record- 
ed in the above field book are Na b; N b c; S c d; S d e; S ef; 
Nfg; 2indiSga. 

274. The same field book w^ill also afford the means of plotting 
or laying down a plan of the estate at any future time. To do 
this, first rule a line N a S, Fig. 78, upon the paper, to represent 
the magnetic meridian, and fix the point a in that line for the 
south-west point of the estate. Put the letter W on the left and 
E on the right hand side of the paper to indicate its east and west 
sides, to avoid mistakes. Then on the point a lay down an angle 
of 7° to the W. or left of the meridian line by a protractor, and 
draw the line a b of indefinite length. Then measure off from 
a scale of equal parts, or a plotting scale, the space intended to 
represent 31.10 chains on the plan, and set off that distance with 
compasses from a along the line a 6, and this will determine the 
point b. Through b draw a second line iV *S' parallel to the first, 
and upon b lay off an angle of 55° 15' to the E. of that second 
line, and this will give the position of b c. Define its length by 
measuring 28.21 chains by the same scale before used, and this 
will fix the point c, through which draw another parallel line in 



134 ON LAND SURVEYING. 

order to obtain the angle S c d, measure off the length of c </ as 
before, and by proceeding in this way the plan will be completed. 

275. The above may serve as a general example of the manner 
in which large plots of ground may be measured and drawn, but 
it generally happens that such plots contain separate fields, roads, 
and other objects in the middle part, which require to be noticed, 
as well as the mere boundaries; and these require to be filled in, 
which can only be done by taking separate measurements of each 
of the fields, and then joining them together. Some defined 
metliod must, however, be followed in this work to prevent the 
plan from becoming distorted, as well as to save labour, and dif- 
ferent surveyors adopt diflferent means to accomplish these pur- 
poses. The principles on which they depend may be divided 
into two heads, viz: working by rectangles or perpendiculars 
with offsets from them, or working by triangulation and offsets. 
Either may be used at pleasure, and may possess advantages in 
particular cases, but the method by triangulation is the most safe 
and satisfactory, and is not attended with more trouble than the 
other. The principles of these operations will be understood by 
reference to the plan, Fig. 79, Plate III., and the following de- 
scription. 

GENERAL DIRECTIONS FOR LARGE SURVEYS. 

276. Walk round the estate before commencing any operation, 
to become acquainted with its magnitude, general form and bear- 
ings, and to ascertain if it contains any elevated positions that 
command views of large parts of it. In cultivated countries, 
roads and lanes, or footpaths, will be found, and examine these, as 
to whether they can be made subservient to the purposes of the sur- 
vey; because if so, they ought to be used on account of their offer- 
ing no impediments to the use of the chain or other instruments; 
wiiile woods, hedges, deep ditches, and other obstacles, frequently 
occasion delay and inconvenience. To guard against these, the 
surveyor should be provided with a small hatchet, as it is fre- 
quently necessary to cut a chain or sight-way through underwood, 
as well as to cut and drive marking stakes. He should also be 
provided with a wallet or strong bag slung over his shoulder for 
carrying the necessary implements and refreshments. If the 
surveyor has to plot or draw his own plans from the measure- 
ment taken, the author recommends from his own experience 
the following distribution of time. To spend the first day in 
the field, taking measurements, and to draw or plot the work so 
taken early the following morning; that done, to resume the 
field work till dark, and on the following morning to plot the 
second day's work, and so on. The reason of this is obvious. 



ON LAND SURVEYING. 135 

Field measuring is laborious and fatiguing work, and after hav- 
ing spent a long day upon it, the operator is in general in no 
condition for fine drawing or scale measuring, his hand is un- 
steady from exertion, and the light of evening is unfavourable 
to his operations. But after a night of refreshing sleep, he will 
be well prepared for drawing on the following morning, when 
the light is good, and he retains a perfect recollection of the po- 
sitions and particulars of the places he has been over on the pre- 
vious day, and may even be able to supply small omissions, if 
such have been made in his field book, and they do not relate to 
measurements. If errors or omissions occur, he detects them, 
and has an opportunity of correcting them by revisiting the spot 
before another day's work is commenced. And as a skilful 
draughtsman will have no difficulty in plotting as much work 
in two hours as can be measured upon the ground in ten or 
twelve, it will be seen that no delay is occasioned by this ar- 
rangement. The drawing work may all be finished before an 
early breakfast, after which the surveyor proceeds to the land, 
and will generally find himself so fatigued after six or eight 
hours' work in the field, (for he should carry his dinner with 
him to avoid delay) that he will have little inclination to do 
more. If the survey is so large as to occupy many days or even 
weeks for its accomplishment, it will be best to divide the land 
into distinct portions which can be finished in a day or two; and 
this is done by setting out straight lines with picket-staves, and 
setting up tall poles with white linen or red flags upon them at 
the angles in order that they may be seen from one station to 
the other, and be known by their colours. Such flags are mark- 
ed at N D S A, Fig. 79, Plate III, and thus the lot intended to 
make one complete survey is inclosed by the right lines ND, 
DB, BA, AS, SN; and if one of these lines, NS, can be laid 
down in the magnetic meridian, and the bounding lines ND and 
SA be made at right angles to it, it will afibrd facility both to 
the work and the plotting; but this must depend on local circum- 
stances. If the plot represented in the plan is supposed to be 
finished, and that another has to be laid out for survey to the 
north of it, then the line ND with its flags will remain stationary, 
and the flags SA are taken down and carried forwards to mark 
out a new terminating line for another plot. In each plot, the 
survey extends to, and ends at these boundary lines, so that the 
work of one plot will fit on to those which join it, and no plot 
must be left until every object upon it is measured and noted 
down. When using a public road for the purpose of surveying, 
never place the theodolite or other instrument near its centre if 
it is much frequented, as the arrival of a carriage, or drove of 



136 



ON LAND SURVEYING. 



cattle may compel you to take it up after it has been adjusted 
and an observation began, and as it cannot be re-adjusted into its 
former exact position it may occasion great inconvenience. 

277. If the plot is proposed to be surveyed by perpendicular 
offsets, it will be best to measure all round it in the first instance, 
as before described (273). Thus taking the plan^ Fig. 79, the 
survey may begin at A, by setting out the right line AB upon the 
road, as far as it continues straight, and measuring it with a chain. 
A would then be called the first station, and B the second. Sta- 
tions are always distinguished in the field book by this mark Q, 
accompanied by a number or letter of the alphabet, and letters 
are the best, because they cannot be confounded with the num- 
bers that express dimensions or angles. The angle that AB makes 
with the magnetic meridian at A, must then be measured by 
planting the theodolite or circumferentor at A, and be entered 
in the field book. In keeping the field book, it is found most 
convenient to begin writing at the bottom of the first page, and 
to proceed upwards to its top, and when full to turn over and 
recommence at the bottom of the next page, and so on until the 
survey is finished; but as this would be inconvenient in printing, 
the following may serve as an example of what would be entered 
in the field book, in the ordinary way of writing from top to 
bottom. 

Survey of an estate called Brookfield, in the Parish of Stow, 
in the County of York, &c., taken February 22nd, 1837. 





OA 




On road proceeding north 


wards to Stow 


at S. E. cor. of Jack. mead. 


Road bears 


N. 14°30'W. 




Width 


00.50 + 1.00 




Ofiset 


5.80 




Hedge and ofiset 


10.30 


cross fence 


Road wide 


00.50 + 1.00 






14.40 


fence 


Jackson's house begins 


16.00 




Road wide 


2.00 + 0.50 




House ends 


19.00 




Road wide 


2.10 + 0.50 




Ofiset 


22.00 




Fence 


22.50 




Road wide 


1.00 + 0.60 






30.00 


road begins and bears S.E. 


Cross roads begins 


31.40 
33.07 






to B and ><! 


road ends. 



ON LAND SURVEYING. 



137 





B at end of X road leading west'd to C 


Cross road bears 


N.72°00'W. 






00.50 to S.E. 


cor. of Thompson's house 


Width of cross road 


2.00+0.60 


to same corner 




2.70 


S.W. corner of house 


Width of cross road 


1.12 + 0.12 






8.70 


fence 




16.50 




Rivulet 


crosses road. 




West side 


17.20 


of do. 


Width of road 


1.00+0.25 






23.00 


fence 




27.50 






to O C in the 


meridian boundary. 





O C in last 


road at mer. boundary 


Width of road 


1.00+0.25 




Bearing 


due S. the 


west'n. mer. boundary 


Offset 


6.00 




Rivulet begins 


10.00 




Fence 


10.50 




Rivulet ends 


11.00 




Fence 


26.00 




Fence 


37.00 






to S in the 


south boundary. 



Bearing of O A 
Fence 



S. 



O S in the 
90° 00' E. 

8.50 

19.50 
to O A 



west boundary line 



278. After what has been before said, it is presumed little 
further explanation need be given of the entries in the field book. 
They commence by giving the position of the first station, and 
the angular direction in which the survey proceeds, and the first 
right line being set out upon a road, the width of that road is 
given occasionally, not in one direct measure, but in two sums, 
as 00.50+1.00, because all things in the field book bare relation, 
in position, to the line set out. Every thing that occurs on the 
left hand side of that line is placed in the left hand column, the 
central one is reserved for lengths and bearings, and the right 
hand one for what occurs on the right hand side; and as the sight 
line is not in the centre of the road, the 0.50 indicates that the 
road is 50 links wide to the left of the line, and one chain wide 
to its right, making a total of 1.50; and if the sight line had not 
18 



138 ON LAND SURVEYING. 

been upon the road, its measure would have been so expressed. 
At 5.80 chains an offset occurs, that is to say, a perpendicular to 
the line has to be measured on the left side,, for determining the 
positions of two cross fences a and h. This point in the survey 
is determined by looking at the point b through a surveying 
cross, or by setting the theodolite to 90°, and it must be mark- 
ed on the road by leaving a picket-staff at c; and as this offset is 
on the left hand side of the road, it is set down in the left hand 
column. At 10.30 a hedge occurs on the left, which, being per- 
pendicular to the line, is also made an offset, marked by a picket- 
staff, and set down in the same column, but the cross fence oppo- 
site to it, on the other side of the road, is put in the right column. 
The next fence occurs on the same side at 14.40, and is entered 
in the same column. At 16 chains on the left a house begins, 
and at 19.00 it ends, and here the road widens, as indicated by 
its entry. At 22.00 a left hand offset must be picketed, to be 
taken as before, to fix the positions of d and the rivulet e. At 
30.00 chains a cross road begins on the right, and bears off to 
S. E.; and at 31.40 a cross road begins, and at B, the end of the 
line, it terminates; and the first station being thus far completed, 
a double line is drawn across the book. 

The second station O B to C; the third from C to S: and the 
fourth from S to A, bring the surveyor back to the point at which 
he commenced; and now he has to go over the same ground again 
for the purpose of measuring the offsets that were passed in the tirst 
round, with a view to prevent mistakes or confusion, with no 
other notice than a memorandum of the place of their existence. 

279. In the second circuit of the plot no notice is taken of any 
thing but the picket-staves that had been left to mark the places 
of offsets; and the book must at the same time be searched for 
them, to ascertain that none of them have been removed. The 
first that occurs is at 5.80 in the book, and at c in the plan. Fig. 
79, and this is measured from c to «, and turning out to be 12.70 
to the fence, is so entered in the field book against the words 
"Offset No. 1,'^ previously written, (see the next page where this 
same field book is repeated, with all its additions in the inverted 
order, or that in which it would be written; consequently the 
reading of it must commence at the bottom and proceed upwards.) 
The measurement is, however, continued from a to 6, in order 
to fix the position of the point 6, and this making the total length 
of the offset 21.25, is accordingly entered more to the left in the 
same line. 

The next left hand offset that occurs is at 10.30 in the book, 
and./' in the plan, and this is taken in the line of a fence; its 
length 10.50 is set down with a remark, that two fences meet at 



ON LAND SURVEYING. 



139 



this point, and a sketch of their form is given, for this mode of 
sketching is constantly resorted to in field book entries, and as- 
sists very materially in laying down the plan, but cannot be well 
imitated in printing without cuts or diagrams for the express pur- 
pose. The next remark occurs at 16.00 chains, where we find 
a house begins and continues to 19.00, thus showing that house 
and premises to be three chains long; and the remark of the left 
hand side of the road being extended to two and a half chains 
from the sight line, shows how far that house stands back from 
the road. The figures 2.12 and 1.25 introduced in parenthesis 
before the w^ord house, shows the depth of that house in links at 
its two ends. The third ofiset is at 22.00 left, and the figures 
and mark set against it, show that at 18.50 it meets a cross fence, 
making a salient angle, and at 22.00 it comes into contact with 
a rivulet, which ends this line. At 22.50 a fence occurs on the 
left, and another width of the road is given. At 30.00 a road 
presents itself on the right, and ends at 33.07, which determines 
its width; and at 31.40 a road appears on the left, the width of 
which is not determined, and this ends the first station. 

In the second station from B to C no ofisets are necessary; and 
only one occurs in the third, because the points already ascertained 
will be sufficient to determine the positions of all the cross fences. 

280. COPY OF PAGE 1 OF THE FIELD BOOK ABOVE REFERRED TO. 





to O B and X 


road ends 




33.07 




Cross road begins 


31.40 






30.00 


a road bearine S. E. 


Width of 


1.00+0.60 


road 


7 Fence 


22.50 




Riv'let22.05X! ^ ofi'set. 


22.00 




fence> 18.50 5 No. 3. 




Width of 


2.00 + 0.50 


road 


(1.25) house ends 


19.00 




Width of 


2.50 + 0.50 


road 


(2.12) Jack's hou. begins 


16.00 






14.40 


fence 


Width of 


00.50 + 1.00 


road 


2 fen. meet> ^ hedge and 
10.50 5 off"., No. 2. 




/« 


10.30 


cross lence 


X f. in m.b. 21.25 ) ofi*set, 
(fence 12.70) 5 No. 1. 


5.80 




- 


Width of 


0.50 + 1.00 


road 


Bearing of road 


N. 14° 30 W. 


proceeding north to Stow 




O A 


from S.E.cor. Jack.'s m. 



140 



ON LAND SURVEYING. 



PAGE 2 OF FIELD BOOK. 



Fence 



to O A 
19.50 
8.50 



Bearing ofS. 90° 00' E. 

I OS in 



and survey ends 

station A 

west boundary line. 



To OS 


in the south 


boundary line. 


Fence 


37.00 




A cross fence 


26.00 




Rivulet ends 


11.00 




A cross fence 


10.50 




Rivulet begins 


10.00 




7.00 to rivulet. Ofifset 


6.00 




Width of 


1.00+25 


road 


Direction 


due south on 


the west'n.mer. boundary. 




0C 


in last road at do. 



Width of 

Rivulet crosses 

East 

Width of 

Width of cross road 

Cross road 



to O C in the 

27.50 

23.00 

1.00+0.25 

17.20 

16.50 

8.70 

1.12 + 0.12 

2.70 

2.00 + 0.60 

00.50 

N. 72° 00' W. 

OB at end o 



meridian boundary 

fence 
road 
the road 
side of rivulet 
fence 
road 

S. W. cor. Thompson's ho. 
to same corner 
S. E. corner of house 
bears 
f X road lead'g west'd to C 



281. The upper part of the plan BC ND might be treated in 
the same manner, but it is believed that enough has been said on 
the method of perpendicular offsets, to render that operation per- 
fectly plain, and the upper remaining plot will, therefore, be sur- 
veyed by triangulation; for which purpose begin at B, and set 
out the right line BD for measurement, when the following field 
book, read from bottom to top, will, with reference to the plan, 
explain the operations and measurements that must be made. 



ON LAND SURVEYING. 



141 







PAGE 


1 OF FIELD BOOK. 






at station B 


N. B. This finishes the 








first triangle. 






27.50 






Width of 


1.00 + 1.50 


road 




House ends 


27.00 






Width of 


0.12 + 1.50 


cross road 


Angle of a house 


25.00 






Width of 


0.25 + 1.00 


road 




Cross fence 


19.00 






Width of 


0.25 + 1.50 

12.60 
C 10.80 


cross road 


• 


Rivulet 


< crosses the 
( 10.00 


cross road 




Cross fence 


4.75 






Width of 


0.25 + 1.00 

S. 79° 30' E. 


road 




C to 


B bearing in 


aX road; and left the theo- 








dolite there. 




To 


S. W. angle 
32.00 


C 


To fence 


2.501 








To river 8.50 
To X fence 13.00 


> offset 


25.00 


cross fence 


ToB 


24. 50 J 










Cross fence ~) 






To fence> 


1.60. Offsets 


16.60 


cross fence 






13.75 


off. 1 8.00 to ext'me point N 






S. 37° 90' W. 






D to 


C bearing 





•>11.00to 
• X fence 



X fence and 
offset 
Width of 
To centre of 



Toriv't&tofence^ offset, 
N. & S. 7.75 5 No. 1 
House ends 
Angle of house in line ] 
with road ' 

Width of 

B toD 



to O D 
35.00 
24.12 

22.00 

0.74 + 0.12 

a bridge over 

15.00 

12.00 

3.00 

1.00 

0.50+1.00 
N. 6° 80' W. 
bearing 
OB 



cross fence 



bridge 

rivulet 1 chain wide 



road 



142 



ON LAND SURVEYING. 



PAGE 2 OF FIELD BOOK. — Survey ends. 





at station D 






■ 22.66 


no offsets or remarks 


' 


S. 90° 00' E. 






ON 


bearing to D the extreme 
N. E. point 





to station N 






29.50 






13.33 


cross fence 




N. due N. 






O C 


bearing to N the extreme 
N. W. point 



282. On examining the above field book it will be found that 
the operations therein detailed divide the estate into two tri- 
angles, B D C and C N D, and in measuring each side of them all 
the positions of fences, and other objects, become fixed in the 
outer boundaries, while their internal positions are, in like man- 
ner, fixed upon the diagonal CD, or main offsets Ng and B h, so 
that no line occurs on the land, the position of which is not fixed 
by at least two, if not three, points. 

283. The student will do well to draw plans from these field 
books without looking at the plan on the plate, using any scale 
at pleasure; and likewise to triangulate the lower part of the 
plan A B C S, and make his own field book from the same, as 
such practice will facilitate his operations in the field. Such 
drawings will only require compasses to measure, together with 
a scale of equal parts to obtain the lengths, and a protractor to 
lay down the angles. 

284. As before mentioned, the regular business of a Civil 
Engineer is separate from that of the Land Surveyor or Measur- 
er, and he is therefore seldom called upon to survey large tracts 
of land. But should that become necessary it is hoped that the 
directions above given, aided by practice and experience, will 
enable him to perform such duty. It is impossible to give rules, 
or lay down principles that shall apply to every case; but the 
great principle to be observed is to obtain right lines of sight as 
long as possible, and to dispose them, so that one shall fix and 
determine the position of another, and the more simply this can 
be done, the less labour there will be in the operation. No 
disposition of lines does this so effectually as the triangle, conse- 
quently no process can be so good as that which reduces the lines 
to that form; and their careful measurement, and an intelligible 



ON LAND SURVEYING. 143 

record of them in the field book cannot fail to produce a good 
plan, 

2S5. When the land to be surveyed is very extensive, so as 
not to permit the lines to be measured on account of their great 
length, inequalities upon the surface, interposition of large 
rivers, bays, mountains, or other impediments, the processes of 
trigonometry must be resorted to, as is the case in preparing 
maps of whole countries. In this case it often happens that the 
exact positions of towns, villages, and other objects, spread over 
a large extent of country, may be correctly ascertained by the 
actual measurement of only one single line upon the ground, to 
serve as a base. Because, if two distant church spires or other 
well defined objects, can be seen at once from the two ends of 
such base line, then a good theodolite placed at those ends, will 
form two triangles, two sides of which are visual, while the mea- 
sured base forms the third side common to them both, and thus 
will sufficient data be established, not only to determine the dis- 
tance the two objects are apart, but the distance of either of them 
from the ends of the base line, and this with greater precision 
than if their distances had been mechanically measured. The 
original base line may now be deserted, and one of the newly 
ascertained distances used as a second base line, to repeat a 
similar operation on two other distant objects, and thus may 
a series of triangles be extended from one part of a territory 
to another, all founded upon the original base line. This is call- 
ed a trigonometrical survey, and is the kind of survey that has 
been long in progress, and is nearly completed in Great Britain, 
and is now proceeding in the United States, being conducted by 
detachments of the corps of Military Engineers, as noticed in 
the introductory chapter. The main triangles having been thus 
established, the interior parts of them have to be filled up by the 
ordinary processes of surveying already described. 

286. The kind of land surveying the Civil Engineer has most 
frequently to attend to, though extensive in length, is seldom so 
in breadth, and is of a very simple nature; for it is generally 
limited to the examination and measurement of a tract of country 
through which a road or canal has to pass. A road or canal may 
be found necessary between one town or city or several of them, 
but still it can never be laid down upon a map, since its perfec- 
tion, and even the possibility of its execution depends, in great 
measure, upon the face formation and materials of the country it 
has to pass through, and these can never be judged of by a map. 
All that the map can do is to point out the relative bearing posi- 
tion and distance of the places from each other, and the general 
form of route to be pursued, and that being settled the Engineer 



144 ON LAND SURVEYING. 

must inspect the ground in order to find out the best and nearest 
route, and to ascertain if the project can really be carried into 
execution. The selected line having been staked or marked upon 
the ground, has to be levelled by operations that will form the 
subject of the next chapter, and this process of levelling will 
show at once whether the line selected is a favourable one or 
not. If it should prove so, it may be considered as fixed, but if 
otherwise, it must be deserted, and a new line selected out. 
JEven though the first line may present no formidable impedi- 
ments, and may appear tolerably good, it is often necessary to 
examine and level other lines contiguous to the first, in order to 
ascertain if one that is better can be selected. It will thus ap- 
pear that the Engineer's line must be selected and marked out 
before any survey becomes necessary, and as his operations sel- 
dom extend to a hundred yards on either side of the line selected 
for the work, his land surveying operations need seldom exceed 
that limit. He will have to ascertain the shape and dimensions 
of those fields and lands he has to cut through, and of those im- 
mediately joining to them, but will have no occasion to pene- 
trate farther into the property, and the whole of his measurements 
may be perfornted by the chain, cross and circumferentor, or 
even by a levelling instrument with a large compass attached to 
it; for a levelling instrument with a large and good compass is 
the best circumferentor he can have, as will appear in the next 
chapter, where that instrument is described. 

287. As an example of the manner of setting out and survey- 
ing for a road or canal, suppose C, Fig. 80, Plate III., to repre- 
sent the plan of a town situated in a hilly or gently undulating 
country, and that it has become necessary to construct a road or 
canal between it and a neighbouring village V. The nearest or 
most direct course for communication would be in the direct 
line CV, as shown upon a common map in which hills and val- 
leys are not indicated. But upon examining the country it will 
be found that a hill exists at a (as indicated by the shading in 
the figure, which is so shaded to show the manner in which hills 
and valleys are represented upon maps when they are drawn) 
which must be ascended, as more clearly shown in Fig. 81, 
which is a section or profile of the same country, and in which 
the same letters of reference indicate the same places. That hill 
must afterwards be descended to get into the valley, after which 
a second ascent takes place over the hill c followed by a descent 
to d, and ascent to e, and finally a descent to V, so that although 
this line might be formed into a road, it would form a very hilly 
one, without expensive excavation and embankment, and would 
not be a desirable line; and such a one as would almost preclude 



ON LAND SURVEYING. 145 

the construction of a canal. Another line should consequently 
be sought for before an actual survey of the ground was com- 
menced. If, instead of following the right lined direction, the 
surveyor turns his attention to the valley between the hills, he 
will be able, very probably, to select a line to f that shall be 
nearly or perfectly level. From thence proceeding to g he ob- 
tains another similar line, and another from g to V. This last 
line would consequently be the one that he would stake or mark 
on the ground for levelling and surveying. If a supply of water 
could be obtained for it, it would be well suited for a canal, and 
on the contrary, if not too wet, from being in the bottom of a 
valley, would make a good and level road. But should a rivu- 
let or water-course in the bottom interfere, he would only have 
to run his line C f further out, as to A, and to carrry the line of 
road a little distance up the brow of the hill in the direction of 
the line h i V, when no other inconvenience will arise from the 
water, except that it will probably be necessary to build a bridge 
or culvert for passing over it at V or/J or perhaps in both places. 
If this increases the expense considerably, he will examine the 
other side of the valley to ascertain if they can there be dispens- 
ed with. 

288. Presuming, however, that the line C f g d Y has been 
selected, the process of surveying it will be very simple. The 
circumferentor is first placed at C and directed to yj and the an- 
gular bearing of C /" with the magnetic meridian noted down. 
This line is now measured by the chain, and every fence that 
crosses it, noted down to the right and left of it, taking at the 
same time such ofiset lines perpendicular to C /" by the cross or 
circumferentor as will fix their angular positions in respect to that 
line, as well as their cross or longitudinal boundaries. That 
done, the instrument is shifted iof, and the bearing of/g to the 
meridian is next taken, and then its cross fences, houses, and 
other objects as before. The same thing is now repeated at the 
station g looking to V, and nothing more than a repetition of 
the same operations will be necessary, however extended the 
line may be. 

2S9. The levelling, or rather determining whether the line 
selected is really level, or how much it deviates from a level, is 
always performed before the survey is made, as was before ob- 
served; because the value of the line is determined by its ap- 
proximation to a true level. As, however, the process of 
levelling has not yet been explained, the method of performing 
this operation will be detailed in the next chapter, where it will 
be fully described. 

290. There is one other circumstance connected with land 
19 



146 ON LAND SURVEYING. 

measuring that has not yet been alluded to, but which in practice 
requires particular attention when the ground is hilly or uneven, 
but need not be regarded in level countries. This is, that as all 
plans are drawn on flat paper, and the ground measure must be 
taken upon the surface of the land, if that land is uneven there 
will be a want of accordance between the limits laid down on 
the paper and those obtained by actual measurement. Thus, 
for example, in Fig. 81, Plate IIL, the right line Q> k I Y 
may represent the flat surface of a sheet of paper upon which the 
plan is to be drawn. Then for the plan to be correct, it is re- 
quisite that every object should appear in its relative propor- 
tional place. The town C should be at C on the paper, the valley 
b at b, and the valley d at d; but since the measurements by 
the chain must be taken from C over a to b, the curved line C 
a b \s evidently longer than the right line C b, consequently, 
when this measurement is transferred by scale to the paper, the 
point b will become shifted to k. Again measuring the whole 
curved line C a b c dthe point d will be found at /, and hence on 
consulting the plan it will appear that we have a greater exten- 
sion of land than what really exists in nature; and it is this error 
that requires correction and adjustment, in order that the mea- 
surement taken on the land, and that upon the paper, may be in 
perfect accordance. 

291. Land surveyors in difierent countries, and even in differ- 
ent districts of the same country, do not appear to have come to 
a decided determination, whether the sloping surface should be 
considered as the quantity of land to be reported to the land 
owner, or whether that quantity should be reduced to a horizontal 
plane. This difference of opinion arises from the sloping surface 
being in every case larger than the horizontal one, and being 
capable of growing more grass, corn or other low vegetable pro- 
ducts, and consequently affording more animal provision than 
could be obtained on the horizontal plot. On the other hand, 
no more trees can grow on the side of a hill than would grow on 

• its horizontal area. And if a pale fence has to be set in a direc- 
tion ascending a hill, and the pales are to be 6 inches, or any 
given distance asunder, it will require no more pales to form 
that fence than if it ran horizontally, the pales still being the 
same distance apart. The only difference will be that the pales 
will be further apart where they touch the hill. No question 
has, however, arisen as to the propriety and even necessity of 
reducing all sloping lines or surfaces to their actual horizontal 
extent in drawing plans, because without this precaution, all 
plans of hilly countries must become distorted, and this reduc- 
tion should in consequence be always made. 

292. To accomplish this reduction, the hill or slope is always 



ON LAND SURVEYING. 147 

considered as a right angled triangle; the hypotenuse being the 
slope, while the base is the horizontal distance. On this account 
the operation is called reducing hypotenusal to horizontal mea- 
surements. To solve this problem on the ground it becomes 
necessary to ascertain the angle that the slope of the hill makes 
with the horizon, and this is one of the purposes of the verti- 
cal graduated circle e of the theodolite, Fig. 77. 

To take this angle, plant the theodolite at the foot of the hill, 
and adjust it by making its horizontal plate truly level. Then 
placing a stick in an upright position close to the instrument, cut 
it off at a height equal to the centre of the axis/^of the telescope, 
carry this stick to the top of the hill and direct the horizontal 
cross line of the telescope into such position that it may appear 
to touch the top of the stick; or take a levelling staff (described 
in the next chapter,) and slide the centre line of its vane into 
such a position that that line may be equal in height to the axis 
of the telescope when the staff stands on the ground, and carry 
the vane so adjusted to the top of the hill, instead of the stick, 
and observe it as directed with the telescope, when the vernier 
of the semicircle will give the angle of elevation of the hill. It 
was before mentioned (269) that the vertical semicircle of the 
best theodolites was divided on one side into degrees for measur- 
ing angles, and on the other, into a scale for converting hypo- 
tenusal into horizontal lengths. And if the instrument contains 
such a scale, no further operation will be necessary; because, 
when the telescope stands at any angle, the number of links and 
parts of links to be deducted out of each 100 links of hypote- 
nusal length, will be indicated by the engraved figure that 
stands opposite to a pointer or index on the corresponding side 
of the vernier block; and on deducting such number of links 
from the measurement obtained, the remainder will give the 
true horizontal length to be used. If the instrument has not 
such a scale, then after taking the angle, the hypotenuse of 
which has been measured, the base length may be obtained from 
the table printed at the end of this chapter, or by stating the fol- 
lowing proportion, viz: 

As radius : 100 links of hypotenuse :: cos of angle of eleva- 
tion : to base sought. 

For example, suppose the angle of the hill to be 29° 30' then 
by logarithms — as radius - - - 10.000000 
: 100 links of hypotenuse 2.000000 
: : cos of angle 29° 30' 9. 939696 

11.939696 
— Radius 10.000000 
: Base 87 links - 1.939696 log. of 87, 

or 13 links short of 100; so that 13 links must be deducted from 



148 



ON LAND SURVEYING. 



each 100 links or chain of the hypotenusal length, or in that pro- 
portion for a smaller quantity. 

293. If the slope of the hill is not regular, but inclines more 
in one part than another, so that the slope cannot be considered 
a right hypotenusal line, as is the case with the side of the hill be- 
tween a and 5, in Fig. 81, and which cannot be correctly ascer- 
tained until the slope has been examined by levelling; such 
slope may be divided into one or more reaches or divisions, the 
angles of which may be taken separately. Thus, in the figure, 
the slope from the summit a to m is very gradual; from m io n 
is very steep; and from ?i to 6 is nearly a mean between the two. 
Three angles must, therefore, be taken between the slope and the 
horizon or level line, viz: one at tu, one at n, and one at h; and 
if a separate computation is made for the length of lines in these 
three spaces, their sums added together will produce a much 
nearer approximation to the true horizontal extent, than if only 
one angle had been taken at h, and the curved line am n h had 
been treated as a right lined hypotenuse. 

294. A TABLE 

For shortening the hypotenusal line, in plotting hilly ground. 



The angle of any hill 
with the horizon be- 
ing 

5° 45' 
8° 10' 
9° h^' 
11° 30' 
12° 50' 
14° 4' 
15° 10' 
16° 15' 
17° 15' 
18° 10' 
19° 80' 
19° 55' 
20° 45' 
21° 35' 
22° 20' 
23° 5' 
23° 45' 
24° 50' 
25° 10' 
25° 50' 
^^'^ 30' 
27° 10' 



Deduct from every 
chain's length as 
measured on the 
sloping surface. 

\ link. 
1 

2 

3 
3i 



4i 



5J 
6 

6J 
7 

8 

8J 

9 

9J 
10 

10 J 

11 



The angle of any hill 
with the horizon be- 
ing 

27° 45' 
28° 20' 
28° S^' 
29° 30' 
30° 5' 
30° 40' 
31° 15' 
31° 45' 
32° 20' 
32° 50' 
33° 2b' 
33° bb' 
34° 2S' 
34° bb' 
35° 25' 
35° bS' 
36° 2b' 
36° bb' 
37° 20' 
37° 50' 
38° 15' 
38° 45' 



Deduct from every 


chain's length as 


measured on the 


sloping surface. 


Hi 


links 


12 




121 




13 




131 




14 




14J 




15 




151 




16 




16| 




17 




17i 




18 




18J 




19 




19i 




20 




20J 




21 




214 




22 





149 



CHAPTER V. 



ON LE^^ELLING AND LE^TILLING INSTRUJIENTS, &c. 

295. The term levelling may appear to convey the idea of ren- 
dering a thing level or flat; but, as used by the Engineer and Land 
Surveyor, it applies only to those processes by which the quantity 
of deviation from a true level is ascertained, whether the ex- 
amination takes place for the purpose of determining how much 
a surface must be raised or depressed, in order to render it per- 
fectly level, or for the ascertainment of the precise quantity of its 
slope or inclination, in respect to height, instead of angular posi- 
tion in regard to the horizon. 

296. When a level line, or level plain are spoken of, the com- 
mon idea attached to the expression is that of a right line, or a 
perfectly flat surface, parallel to, or coincident with the horizon 
of the place where it exists. It infers a plain so constructed, that 
if a perfectly spherical ball of uniform density, or a small quan- 
tity of water should be placed upon any part of its surface, they 
would remain at perfect rest, or would show no disposition to 
run from one part of it to another, because bodies acted upon by 
gravitation alone, can only acquire motion by descending. But 
as no one part of the plane is lower than another, the body placed 
upon it could not descend; and therefore would not move at all. 
And whenever a plane exists which fulfils this condition, we 
may conceive it to be perfectly level. 

297. Man sees all objects around him by rays that proceed in 
direct right lines from such objects to his eyes, and is incapable 
of seeing any thing except in these right lines, unless the rays 
of light that convey the image of the object to him should be bent 
or refracted by passing through media of varying density, or some 
other cause; and the height of his eye above the ground is so in- 
significant when compared with the diameter of the earth, that it 
may be said, without sensible error, that whenever he looks at a 
distant object in a horizontal direction, he must look in the di- 
rection of a tangent to the earth's surface. Thus suppose the cir- 
cle E, Fig. 82, Plate III., to represent the earth, and that an 
inhabitant at «, is looking around him. He will be able to see 



150 ON LEVELLING. 

every thing above the tangent line b a c, but nothing below it. 
The line b a c is, therefore, his horizon, and if he turns and looks 
around him in every direction his sight will be limited by a 
horizontal plane formed by the revolution of the line b a c upon 
a as its centre. It may, at first sight, appear that this line or 
plane is level, but upon examination it will not be found capable 
of fulfilling the condition above stated, for if we place the ball or 
quantity of water at d, it will not remain stationary there, but 
will run from d to a; because all things on the earth^s surface are 
held to it by gravitation, tending towards its centre. All bodies 
free to move will, therefore, dispose themselves in a direction 
tending to that centre, and as the line « E is shorter than the line 
d E, so the ball will run down the surface from d to a, and will 
there only remain stationary, because there it is nearer to the 
earth's centre than in any other place. In fact, the angular point 
o{ a d e, projecting beyond the circle, may be conceived to be a 
high hill or mountain, down which, it is well known, a ball or 
quantity of water will run, and not become stationary until it 
reaches the lowest point it can move to, or that nearest to the 
earth's centre. 

29S. From this we infer that to construct a canal or other ex- 
tended reservoir to contain water, its bottom and banks must not 
be right lined, but must partake of the earth's curvature, and be 
concentric with it; thus, in I^ig. 83, if we again conceive E to 
represent the earth, and we imagine a curved table or platform e 
f to be constructed upon it, with its centre of curvature in the 
centre of the earth, any number of balls or quantities of water 
may be placed upon it without fear of their moving; because they 
will be equidistant from the centre of the earth, in all the posi- 
tions in which they may be placed. In constructing canals, and 
building houses or walls, we are in the habit of considering their 
bottoms and tops as right lined when they are level, and they 
may be so considered without fear of practical error, for small 
portions of very large circles may be considered as right lines, 
• and most of our buildings and constructions are of this character. 
Their dimensions are so small in comparison to the length of the 
circumference of the earth, that their deviation from the right 
lined direction cannot be measured or appreciated by any human 
means, notwithstanding our reason teaches us to know they must 
be curved. If, however, the length becomes very extended, 
the difference becomes apparent. Thus, in Fig. 82, if the ball d 
is placed one mile from «, in the right lined direction a b, the 
line d e OY distance from the true circumference of the earth will 
be equal to eight inches. The same reasoning applies to verticals 
or perpendiculars, which are always raised by plumbets. These, 



ON LEVELLING. 151 

like all other heavy objects, gravitate towards the earth's centre, 
and the lines which they indicate will, consequently, converge 
to that centre, like the dotted lines in Fig. 83. It follows, there- 
fore, that the two opposite sides of all buildings radiate instead 
of being parallel, and that the top of every high building must be 
larger than its bottom, but still in so small a degree as to be inap- 
preciable, and it is, therefore, never regarded. 

299. The obtention of levels is an operation of constant occur- 
rence to the builder and Engineer. The bottoms of foundations 
require to be made level before a wall or building can be com- 
menced, and as such walls rise in height, the level position of 
the courses of brick-work or masonry require constant examina- 
tion. No drain for the conveyance of w^ater can be constructed 
without first levelling its bottom and giving it the fall or slope 
necessary for the running of the water. In fixing machinery it 
is frequently necessary to have certain parts of it truly level, and 
in the formation of canals, correct levelling is of vital importance 
to the success of the work; for the water cannot be admitted to 
try its position during the progress of the work, consequently 
the level line at w^hich it is intended to stand must be ascertain- 
ed by other means, and the present chapter will contain an ex- 
planation of the manner in which such level lines are ascertained, 
set out, and examined. 

300. The most common implement used in building for set- 
ting out and proving levels, is the Bricklayer^s Level, the form 
and construction of which is shown at Fig. 84, Plate III. It 
depends on the circumstances of a level line being a tangent to 
the earth's curvature, of a plumb-line disposing itself into the 
direction of a radius of the earth, of course perpendicular to the 
middle of that tangent, and that the level direction is a right 
line. It therefore consists of a board a e, from 1 to 1^ inches 
thick, which should be well seasoned, that it may not cracky 
warp, or change its form; another board b is morticed or otherwise 
firmly attached at right angles to the middle of the first, in such 
manner that their surfaces may be flat or flush. A true perpen- 
dicular line to the under edge of « e (which must be perfectly 
flat and smooth like a ruler) is now laid off from the centre of 
the under side of a e upon the surface of b, and is there strongly 
marked or scratched; a saw cut is made at the top of b in the di- 
rection of this line, from which a plumb-line is supported, its 
weight or bob hanging in a hole d cut through the bottom 
board and large enough to give the bob some play or freedom of 
motion in every direction without contact. The bottom board 
a e should be exactly 2, 3, or 4 yards long from end to end, in 



152 ON LEVELLING. 

order to give results of deviation from level in yards of length 
without calculation. 

If this instrument is correctly made, it will be evident that on 
setting its bottom edge a e on a wall or other surface that is 
perfectly level, the string of the plumbet should accord exactly 
with the line scratched on b throughout its whole length, while 
on the contrary, if not level, the string will be thrown to one or 
the other sides of that line. 

301. To prove the correctness of the implement, place it as 
above, on a surface that it shows to be perfectly level; and such 
a one may always be made by driving wedges under one end of 
a thick plank. After finding that the plumbet hangs in its pro- 
per vertical direction, reverse the level by turning the two ends 
of the bottom plank into the opposite positions they before held, 
when, if the plumbet retains its same parallel position to the line 
on 5, the instrument is perfect. If otherwise, half the error 
must be corrected by raising one end of the plank, and the other 
half by altering the position of the line drawn upon b. By 
several reversions of this kind the true position of the perpen- 
dicular line will be obtained, and then the instrument may be 
used with confidence. 

302. If on applying such a level to a surface, and that surface 
is found out of level, and it is necessary to ascertain how much 
it wants to make it level, as the top of the wall f f, let one end 
a of the level rest on the wall, and introduce blocks of wood or 
wedges under its other end e until the plumbet indicates that 
the instrument stands perfectly level; then measure the distance 
between the top of the wall and underside of the level at a in 
inches, and that will show how much must be added to the wall 
at this place to make it level. Suppose that distance to be 3 
inches, and that the level is 3 yards or 12 feet long. Then the 
deficiency of level will be 3 inches in 9 feet, or 1 inch in a yard, 
or the Y2 of an inch in a foot. 

303. If it is desired to set out a drain to be built under 
ground, such drain being 1 foot high throughout, 1 foot under 
ground at its commencement, and that it shall have a fall or de- 
scent of 2 inches in every yard forward, and that the bottom of 
the level used is 6 feet long, drive a stake even with the surface 
of the ground where the drain is to begin, and other stakes in 
the line of its direction 6 feet apart, or so that the bottom of the 
level will extend from one to the other and can be supported 
upon any two of them. Then, by driving them down, or cutting 
off their tops, reduce them by the instrument to a perfect level. 
Call the first stake A, and the others in succession B, C, D, &c., 
when precise directions can be given to the workmen for digging 



ON 1,EVELLING. 153 

(or as they call it, cutting,) the drain, viz: The excavation 
must be 2 feet deep at A, 2 feet 4 inches at B, 2 feet 8 at C, and 
so on, getting 4 inches deeper at each stake, because the stakes 
are 2 yards apart, and the drain is to fall 2 inches in each yard, 
or 4 inches in the two yards. 

304. This kind of level is made long in order that it may ex- 
tend over a considerable length of work at once; and no brick or 
stone wall should be carried up without applying such a level to 
its top surface at least once in every two or three feet of eleva- 
tion, in order to ascertain that the courses of work are carried on 
in a perfectly level manner. The length of this implement pre- 
cludes its use in many situations, and workmen should therefore 
be provided with a smaller instrument on the same principle, 
but in the shape of a right angled triangle. In this the plumbet 
hangs very near to the perpendicular side, when the triangle is 
set upright on its base; consequently while the base determines a 
level line, the other side of the right angle gives a perpendicular 
one. This kind of level is used by masons for showing when 
the upper surfaces of single stones are level; by carpenters and 
joiners in fixing door posts, jambs, window frames, and such 
things as require to be square and level in some parts and per- 
pendicular in others; and it is frequently used by mill-wrights and 
others engaged in fixing machinery. 

305. The best and most correct instrument for determining a 
true level is the spirit-level, so called from its being usually 
formed by inclosing a quantity of alcohol, together with a small 
bubble of air in a glass tube. It depends on the principle of air 
being much lighter than alcohol or water, and consequently al- 
ways rising above it; so that if a quantity of either of these fluids 
is introduced into a glass tube sealed or closed at both ends by 
the blow-pipe, or what is usually called hermetically sealed, to 
prevent evaporation, and a small bubble of air is also inclosed, 
when the tube is held horizontally the bubble will always re- 
main at the top, and not only at the top, but will get into the most 
elevated position; so that if the tube is sloped in a degree too 
small to be perceived by the eye, the air bubble will always run 
towards, and become stationary in that end of the tube that is 
the most elevated, and consequently can never be stationary in 
the middle part of the tube except when the tube is perfectly 
level. The form of the spirit-level, as above described, is shown 
at J^ig' 85, Plate III., but to fit it for use as well as to protect 
it from injury, the glass tube is always mounted in a brass tube 
equipped with adjusting screws, or more frequently in a piece of 
mahogany or hard wood, and is covered by a brass plate with a 
long hole through it, that exposes the top of the tube and bubble 

20 



154 ON LEVELLING. 

of air, as shown at Fig. SG. The bottom of the block of wood 
being made quite flat and smooth, the level is bedded by gla- 
ziers' putty in a cavity on the top of the block. While the putty 
is soft it admits of either end of the tube being depressed, so that 
it can be brought into a state of perfect level adjustment with 
the bottom of the block, and then the brass plate is screwed over 
it, and when the putty becomes hard it can never alter its posi- 
tion. The adjustment to level is produced by setting the instru- 
ment on a surface that admits of adjustment as to height at one 
end, and making the bubble stand in the middle of the tube. 
The whole instrument is then reversed, end for end, and if the 
bubble still retains its central position the level is in adjustment. 
If not, the end of the tube to which the bubble runs must be 
pressed down further into the putty, about half as much as will 
bring the bubble to the centre, and the other half quantity must 
be produced by elevating the opposite end of the piece it stands 
upon. The same reversion again takes place to try the adjust- 
ment, until the bubble is found to retain its central position un- 
der reversion, when its position will be correct. 

306. It must not be expected that every tube into which alco- 
hol is introduced, as above described, will make a good level, 
since it is absolutely necessary to the perfection of the instru- 
ment that the upper inside surface of the tube, against which the 
bubble of air runs, should be a perfect right line, and this is sel- 
dom met with in ordinary glass tubes. The very process by 
which they are made renders it a rarity to procure a tube that is 
truly cylindrical, or of the same size throughout. They gene- 
rally taper, or are slightly conical, and are frequently curved 
in their length, though in too slight a degree to be visible, until 
they are made into levels, and then, such is the sensibility of 
the bubble of air, that their imperfections become manifest. The 
conical form is not detrimental, provided one side of the cone is 
right lined; because there is no necessity for the bottom of the 
tube being parallel to the top. But if the tube is curved in its 
length, the level will be good for nothing. If, for example, the 
tube curves upwards, or is highest in the middle, the air bubble 
will stand there, notwithstanding a considerable elevation or de- 
pression may be given to its ends; and if it is concave or hollow 
in the middle, the bubble can never be made to stand in that po- 
sition, but will constantly run to and settle itself in one or other 
of the ends. It frequently, however, happens that one side only 
of a glass level may be good, while all the others are decidedly 
bad, therefore a tube should not be discarded until it has been 
turned with every side upwards, and tried in every direction. 
Careful instrument-makers perform this examination, marking 



ON LEVELLING. 155 

the sides that must he placed upwards, and discarding the tubes 
that will not stand the proof. Persons are often surprised at the 
high prices of levels, but when it is known that out of one hun- 
dred tubes filled and prepared perhaps not more than twenty -five 
will stand proof, and out of this last number probably only two 
or three will be found superlatively good, the astonishment 
ceases that a thing intrinsically not worth more than twenty-five 
cents should sell for five or six dollars, before it is mounted or 
any expense incurred about it. The fluid w4th which the tube 
is filled is generally rectified alcohol, because that never freezes 
with the most intense cold, while water, when converted into 
ice, would probably burst the tube. The very finest levels for 
astronomical instruments are filled with sulphuric ether, which 
being more fluid than any other material, offers less resistance to 
the motion of the bubble, and is more sensitive in its action. 

307. With a view to remove the uncertainty of the tube of a 
level being perfectly right lined, the late Mr. George Adams, 
an eminent philosophical instrument-maker of London, invented 
and applied a spirit-level, consisting of two flat plates or discs of 
perfectly flat plate glass, separated by a ring of metal, with all 
the surfaces so closely ground together, that the alcohol and 
bubble could be contained between them, when pressed together 
by a brass ring that surrounded them, without any fear of loss 
by evaporation; and the author has since improved on this prin- 
ciple by grinding the edge of a large watch glass to fit closely 
upon the under side of a circular disc of flat glass, so as to make 
onlyone joint that requires securing, and in which there is no metal 
to act upon or discolour the spirit, and no varying expansion by 
heat or cold in the joint, which may be secured by a cement in- 
soluble in alcohol. In these levels, the air bubble must remain 
stationary in the middle of the top circular disc when it is pro- 
perly adjusted; and such an instrument, surrounded by a brass 
ring with three levelling screws, is a very accurate and conve- 
nient portable horizon, to be used on land with the reflecting sex- 
tant or quadrant. The upper polished surface of the top flat 
glass will reflect ample light for this purpose, but great care is 
necessary in selecting the glass, as both its sides must be perfect- 
ly parallel to insure perfection in the instrument. 

308. The process most usually resorted to for rendering the 
top surface of the ordinary tubular spirit-level truly right lined, 
is to grind that part of the glass tube on a straight iron rod with 
fine emery. This in some measure destroys the transparency of 
the glass, but not in a sufficient degree to prevent the bubble 
being distinctly seen. The best and most expensive instruments 
are constantly provided with ground levels, and as the tube 



156 ON LEVELLING. 

must be open at both ends to admit of the grinding, such tubes 
are not afterwards hermetically sealed, for fear that the heat which 
must be applied for that purpose might warp or bend the glass 
by producing unequal expansion and contraction. The fluid is 
therefore retained in the tube by tying bladder over the ends, 
the joints being further secured by some peculiar varnish that 
has been discovered that effectually resists the action of the in- 
closed alcohol or ether. 

309. Any of the above described instruments will suffice for 
levelling foundations, drains, walls, machinery, or whatever is 
within the reach of the operator. But the pursuits of the Engi- 
neer frequently render it necessary for him to know the relative 
positions as to level of objects that are distant, even miles asun- 
der; as in constructing canals and laying out roads, or water 
works for the supply of towns or smaller establishments with 
water; and whenever this is the case, since no instrument can 
be made that will extend from one point to the other, the optical 
principle, that all things are seen in the direction of right lines 
passing from the object to the eye, must be made use of, as before 
stated in speaking of land surveying. Hence all we have to do 
is to determine when that visual ray comes to the eye in a per- 
fectly level direction, and this may be ascertained by affixing 
sights, such as have been before explained, to any of the instru- 
ments just described for determining levels, observing only, that 
the slits and cross hairs of such sights must now have a horizon- 
tal instead of a vertical position; because in measuring horizontal 
angles, the eye may be allowed any vertical range desired, but 
must have none in a horizontal direction, while in taking levels, 
the eye may range quite round the horizon laterally, but must be 
confined as to vertical position. No sights are, however, so 
good as a telescope with cross hairs, as already described when 
speaking of the improved theodolite, and by reference to Fig. 77, 
Plate II., it will be seen that the telescope as there disposed, 
with a spirit-level beneath it is a levelling instrument, because 

. when the level is set truly parallel to the axis of the telescope, 
and is made level, such objects only can be visible through the 
telescope when moved round in a horizontal direction, as are 
exactly level or equal in height to the telescope itself. 

310. As, however, the theodolite is a very expensive and com- 
plicated instrument, heavy to carry on account of its several brass 
circles and adjustments, and troublesome to adjust at each station, 
simpler and less expensive instruments are made for the express 
purpose of taking levels, and are called Levelling Instruments; 
and Fig. 87, Plate III. exhibits their most approved form of 
construction. The telescope a h, is supported in two Y's, c dy 



ON LEVELLING. 157 

rising perpendicularly out of the main bar e e, and a spirit-level / 
/inclosed in a brass tube that is cut away at the top to expose the 
glass tube and bubble, is attached to the under side of the tele- 
scope. So far, therefore, this instrument exactly resembles the 
corresponding parts of the theodolite already described (269,) ex- 
cept that the telescope is made longer, has more magnifying power, 
and will be more convenient if it shows objects in their natural 
erect position, instead of inverting them. The spirit-level is 
likewise larger, and more perfect, as the chief use of the instru- 
ment is for taking correct levels. The instrument is often made 
without a compass; but if it contains one in the middle of the base 
or bottom bar, as shown in the figure, the instrument becomes a 
circumferentor of a better kind than that before described, inas- 
much as it has a telescope instead of ordinary sights. The Y at 
c is permanently fixed upon the bottom bar, but that at d termi- 
nates below in a square shank that passes into the socket f, and 
is acted upon by a fixed screw, so that by turning its milled 
head the Y and end b of the telescope can be raised or depressed 
about half an inch. The instrument terminates below in a hol- 
low tapering socket h, filling upon a corresponding pivot that rises 
out of the centre of the top parallel plate tu, and the instrument 
is brought into a level position by the four levelling screws k kj 
V ?;, which pass through the upper plate 7n, while their points press 
against the under parallel plate / to which the folding legs that 
support the instrument at a proper height for observation are 
attached. In this figure the heads of the levelling screws are 
shown above the upper plate, instead of being placed between the 
two plates, as in the representation of the theodolite, Fig. 77, 
but this is quite immaterial, for their action is the same in both 
cases; and the intention of making the two figures difierent is 
merely to show the two ways in which these screws are applied. 
2) Is a tangent screw, by turning which the instrument may be 
moved through a small horizontal arc for bringing the vertical 
hair of the telescope into more precise apparent contact with a 
distant object than could be done by hand. 

311. The parts of the levelling instrument being understood, 
the next thing to be attended to is its adjustment, for upon this 
the accuracy of its operation depends; and what is said on this 
subject will equally apply to the telescope and level of the theo- 
dolite. 

312. The first adjustment to be made, is that of the cross hairs 
in the telescope, and this is done in the following manner: 

The hairs are fixed to a brass ring placed within the tube of 
the telescope, and kept in its position by four small screws, three 
of which arc seen at o o n. The eye tube next a is to l^e drawn 



158 ON LEVELLING. 

out until tliese hairs are exactly in the focus of its glass, and they 
are very distinctly seen; after which the eye-tube should not be 
touched again during the use of the instrument. Direct the tele- 
scope to any small and well defined distant object, such as the 
top of a picket-staff set up for the purpose; and, as this telescope ad- 
mits of no vertical motion by the hand, give it the necessary ele- 
vation or depression by turning the screw g. Produce clear and 
distinct vision in the telescope by turning the nut/?, which, by a 
rack and pinion concealed within the tube, projects or withdraws 
an inner tube carrying the object glass b; for all adjustment as to 
focus of objects examined, must be produced by turning that nut. 
Having thus brought the horizontal hair in the telescope into per- 
fect apparent contact with the top or point of the object, turn the 
telescope half round in its Y's, or so that the spirit-level may be 
above instead of below it, and now observe whether the same 
apparent contact between the hair and the object is preserved. 
If it is, the hair is in its right place, but if not, it must be raised 
or lowered as required by tightening the one and releasing the 
other of the two opposite small screws o o, which force it upwards 
or downwards. The horizontal hair being so adjusted, the ver- 
tical one must be treated in the same manner; for which purpose 
turn the telescope so that the spirit-level may be first on one and 
then on the other side of it, which will cause that hair to appear 
horizontal. When both are well adjusted, the crossing or inter- 
section of the hairs, as shown in Fig. 74, Plate 11. , ought to be 
exactly in the axis of the telescope; and that they are so, is known 
by turning the telescope quite round in its Y's, and finding that 
the intersection does not describe a circle round any small fixed 
object, but remains permanently fixed upon it in every part of 
its revolution. 

313. The second necessary adjustment, is to get the spirit- 
level exactly parallel to the axi's of the telescope, or to what is 
called its line of collimation. On inspecting a well made instru- 
ment, or its representation in the figure, it will be perceived that 
the two ends of the spirit-level are fixed to the tube of the tele- 
scope by two distinct modes of attachment, for the purpose of 
making this adjustment. That end of the level next the object 
end b of the telescope, has a rectangular projection of brass which 
passes in between two cheeks r, fixed to the under side of the 
tube, about half an inch asunder, and the level is held between the 
points of two opposite screws that pass through these cheeks, so 
that by tightening one, and releasing that opposite to it, this end 
of the level may be shifted horizontally and fixed in any required 
position, but the joint admits of no elevation or depression of the 
level. The opposite end s, on the contrary, admits of elevation 



ON LEVELLING. 159 

and depression, but of no lateral motion, for the ball s is perfor- 
ated, and a fixed screw, the thread of which works into the tele- 
scope tube, passes through it, so that by turning the screw in 
opposite directions, that end of the level may be raised or de- 
pressed. To use these screws for producing the necessary ad- 
justment, turn the telescope in its Y's so that the level may first 
be on one, and then on the other side of the telescope, level with 
its centre, having previously brought the bubble to its exact cen- 
tral position by turning the nut g, and observe whether the bub- 
ble retains its place in all these positions, and if so, the level is 
right; if not, turn the two screws in r, without touching that in 
s, until the bubble will remain in the centre both when the level 
is put to the right and left hand side of the telescope, and then 
the screws in r are done with and should be permanently tight- 
ened. Next open the two spring-caps that hold the telescope 
down in the Y's, in order that it may be lifted out without dis- 
turbing any previous adjustments, and having brought the bubble 
into its proper position by turning g, lift the whole telescope and 
level out of its place, and invert it by putting the end b into the 
Y c and the end a into the Y dj and observe whether the bubble 
retains its central position. If so, the level is in its right posi- 
tion; if not, the bubble must be brought to the centre by giving 
half the necessary motion by the screw at 5, and the other half 
by that at g. Having got the bubble into its right place, the 
telescope must be again taken out and reversed into its former 
position, when most probably a little further motion of the screws 
at s and g may be necessary, after which the telescope is to be 
reversed again, and so on until it is found that the bubble steadily 
maintains its position in every position, while that of the Y's re- 
mains unchanged. If the instrument will not bear this test of its 
correctness, some radical error of construction, or fault in the 
level, must exist, which can only be cured by returning it into the 
hands of its maker, or other competent workman, for correction. 
All the above are called the permanent adjustments of the level, 
because when once made they never require to be repeated, un- 
less some of the screws are inadvertently turned, or the instru- 
ment receives an injury. All the screws that efiect permanent 
adjustment, should have small square heads to be turned by a 
socket-key, such as is used for winding watches, or should have 
v/hat are called capstan heads, or small holes drilled in their 
heads to admit a pin for turning them, in order to render them 
as difficult to turn as possible without possession of the necessary 
key or implement. 

314. To adjust the instrument for taking an observation, or 



160 ON LEVELLING. 

for use in the field, which is a temporary adjustment requiring to 
be repeated at every observation that is made. 

Before taking the instrument out for use, it is presumed that 
all the jDermanent adjustments, just described, have been pre- 
viously made. Open and fix the three legs of the stand in such 
manner that the instrumentmay stand firmly on the ground, with 
the lower parallel plate / as nearly level as the eye can set it. 
Release the tangent screw jo (if the instrument has such a one, 
which is not always the case,) and turn the instrument round 
upon its pivot A, until the bottom bar e e stands directly over any 
two of the levelling screws, k k for example. Then by turning 
those screws, viz: screwing the one and unscrewing the other in 
an equal degree, so as always to maintain a moderate ^^I'essure 
against the bottom plate /, the upper plate m will be moved, and 
as the instrument goes with it, the bubble of the level will soon 
be brought into its central position. That being effected, turn the 
instrument a quarter round, so that its bottom bar e e may be 
brought over the two other levelling screws v v, and use them like 
the two first, until the bubble is brought to the centre in this new 
position of the instrument. This last adjustment will most proba- 
bly disturb that before made, therefore turn the instrument an- 
other quarter round in the same direction as before, in order to 
bring it again over the two screws k k, but with the ends of the 
telescope in opposite directions, and now once more turn the 
screws kk if necessary, and the instrument, (if these adjustments 
have been well made,) will be ready for use; to prove which, turn 
the instrument completely round on its pivot p, and observe if 
the bubble remains stationary during the whole circuit, if so, it 
is well adjusted, if not, all the operations just described have to 
be repeated, again and again, until the bubble is found immove- 
able. This is a troublesome operation, requiring time and pa- 
tience, but it must be submitted to, if correct results are desired, 
and has to be repeated at every distinct station on which the in- 
strument is set up for use. 

315. As the levelling instrument is costly, and may not be in 
the possession of many who may desire to ascertain levels for 
constructing water courses or other purposes, the following de- 
scription of two other instruments that will answer the purpose, 
though in a less perfect manner, may be acceptable, particularly 
as they may be constructed by ordinary workmen in almost any 
place. 

The first depends on the principle of the surface of water al- 
ways being level, whatever may be the shape of the vessel that 
contains it, and the second is dependant on the plumb-line. 

The first, or water level, may be made by any tinsmith or car- 



ON LEVELLING. 161 

penter, from the following description and representation of the 
instrument, Fig. 89, Plate III. Two equal sized square boxes 
a and b, about an inch square, and six or eight inches high, are 
united together by about eighteen inches of half-inch tin pipe c, 
that enters both the boxes close to their bottom, and for the sake 
of strength, the whole may be fixed to a bottom-board. Water 
poured into either box will run through the pipe into the other, 
and the surface of the water in both boxes will stand at the same 
level, notwithstanding any inclination that may be given to the 
bottom-board. If, therefore, two sights, d and e, made of tin, 
fastened to the tops of two square corks or bits of light wood, less 
than the boxes, be introduced into them, they will float, and if of 
equal weight, and the sights, one formed by a hole or horizontal 
slit, and the other by a frame with a thread across it, are of equal 
heights from their bottoms, a level line will be obtained on apply- 
ing the eye to them, without any care as to the precise position 
of the bottom-board. The boxes and floats are made square to 
prevent the sights from turning round. Such an instrument may 
be mounted on a stand, and will answer many purposes for short 
distances. 

316. The plumbet level may be made wholly of wood, and is 
simple in its use and construction. Cause a wooden, tin, or other 
metal tube a, having a bore of three-quarters of an inch, to be 
fixed upright in the middle of a triangular wooden foot b, Fig. 
90, which has a levelling screw passing through each of its cor- 
ners. A cylindrical rod c is provided of such size as to fit into 
and move round in the tube freely, but without shaking, and to 
the upper part of this rod attach a thin right angled piece of wood 
f d e, having a line and plumbet g hung against the perpendicular 
side d f, and two sights on the horizontal top d e. The triangle 
with its sights and plumbet must be fixed to the rod c, in such 
manner that it may balance or have no tendency to throw the rod 
to one side or the other. This constitutes a very cheap and ef- 
fective instrument for short distances, and if the rod c is of turn- 
ed metal, and the whole well made, and a small common telescope 
is attached to the top instead of the sights, it will perform pretty 
accurate work. It may stand on a table or be mounted on a three- 
legged stand like other instruments, and is adjusted like the level 
by first turning the triangular board, d e f, into the direction of 
any two screws, and by their means causing the plumbet to hang 
in coincidence with the line drawn for it, and also parallel to the 
face of the triangle. That done, the triangle is turned upon its 
stem c, to a position at right angles to the first it held, when it 
will be over the third screw, and between the two first. The 
adjustment is now rendered more perfect by the third screw, and 
21 



162 ON LEVELLING. 

will not be complete until the triangle can be turned quite round 
without altering its position in respect to its plumb line, or its 
parallelism with respect to the face of the triangle, and whenever 
that is found to be maintained, the instrument is ready for taking 
an observation. 

317. In these, and all other modifications of the levelling in- 
strument, the line of sight is straight, and may be considered a 
tangent to the earth's surface at the place of observation; conse- 
quently supposing the instrument to be placed at a. Fig. 82, the 
level line given by the instrument will be that indicated hy a b 
or a c, called the apparent level, and the manner in w^hich this is 
converted into a curve, concentric with the earth or a true level, 
will appear when the method of using the instrument is ex- 
plained. 

318. Whatever may be the construction of the levelling in- 
strument, it is constantly used in conjunction with a measuring- 
rod, of a peculiar construction, for determining the height of the 
several objects above or below the level line, and such implement 
is called a levelling-staff and vane. The vane, or target, as it is 
called when circular, is the object to be looked at by the telescope 
or other sights of the levelling instrument, and is made to slide 
so stiffly upon the rod, (which is divided into inches commencing 
from the bottom,) that it will remain without shifting in any 
place at which it may be put. The form of the rod is not ma- 
terial, provided it is straight, and it should be ten or twelve feet 
long, painted white, with the inches and quarters painted in black 
upon it. The target is often made of strong tin-plate, painted 
black and white in quarters, as in Fig. 88, so as to mark the cen- 
tral horizontal line distinctly at a distance; and the hole in the 
centre is to permit the figures and divisions to be seen through 
it, the division corresponding with the horizontal line being 
pointed out by a fine wire soldered across the hole. The target 
frequently has a tin socket, for the rod to slide through, soldered 
behind it, and a thumb screw to fix it at any required height upon 
the rod, which, for the convenience of carriage, is made in sepa- 
rate pieces, six feet long, that screw together, end to end. When 
the required elevation of the target is so great as to be beyond 
the reach of a man, it becomes necessary to slope the rod, in order 
to reach and shift it, when it is again held upright, but as this 
operation has frequently to be repeated many times at each sta- 
tion, it becomes troublesome and tedious, and the form of the 
best London staves is preferable, as the adjustment is performed 
at once. The London form of staff and vane is shown at Fig. 
91, Plate III. The rod is about one and a half inches square, 
and six feet six inches long, made of mahogany, inlaid on its face 



ON LEVELLING. 163 

with holly, or other white wood, to receive the divisions and 
figures. The staff consists of two pieces dovetailed into each 
other throughout their whole length, so that one half of the rod 
slides upon the other, in consequence of which the rod can be 
pulled out or extended to twelve feet long, and yet will leave a 
foot of the two halves jointed together, for maintaining the straight 
form of the instrument. The divisions begin to count from the 
bottom of the staff, and are engraved upon its front in the manner 
shown at Fig. 92, viz: a double scale of divisions runs up the 
middle of the front of the stafi*. The one side consisting of feet 
and inches divided into tenths, and the other of feet divided into 
hundredth parts, without regard to inches; but every tenth di- 
vision is numbered. This double scale is for the convenience of 
taking levels directly in inches and tenths, or in feet and hun- 
dredths, and the latter is so much more easy and simple, that it 
is almost universally used, though the contiguous scale of inches 
is very convenient for converting decimals of a foot into tenths 
of inches by inspection, without calculation. These divisions 
terminate at six feet in height from the bottom of the scale. The 
vane is a thin piece of mahogany, ten inches long and three wide, 
having projections behind, which form a socket fitting the rod, 
in order that it may slide up and down upon it, and this sliding 
is rendered more equable and certain by a flat spring contained 
in the socket, which produces sufficient friction to cause the vane 
to remain wherever it may be placed. The form of the vane is 
shown at a 5, Fig. 91; its front is covered by white wood or pa- 
per, but has two strong black lines marked upon it, each half an 
inch wide, leaving a white line a quarter of an inch wide between 
them; and in using the instrument the horizontal hair of the le- 
velling telescope must be made to appear to be upon the middle 
of this white line. There is a hole in the centre of the vane to 
show the figures on the staff, and the edges of this hole are cham- 
fered to admit as much light as possible to fall on the figures or 
divisions, and a horizontal wire crosses the hole, at the middle of 
the white line, to point out the division on the scale that corre- 
sponds with the height of this line on the vane. The staff being 
placed on the ground in a vertical position, is so held by one hand 
of the assistant, (called, in this case, the staff-holder or rod-man,) 
while with the other he elevates or depresses the vane, according 
to the directions or signals he receives from the person at the 
levelling instrument; because, as the telescope of that instrument 
admits of no elevation or depression, the vane must be raised or 
lowered upon the staff, until it is brought into exact apparent 
coincidence with the horizontal hair of the telescope. When the 
cross wire of the vane is raised so high as to intersect six feet, 



164 ON LEVELLING. 

there is a stud or stop on the staff that prevents its being pushed 
higher. If, therefore, a greater height than six feet is required, 
the vane is put to this height and is not to be touched again, but 
the staff-holder holds the back portion of the staff cc, Fig. 91, 
with one hand, keeping it still upon the ground, and with the other 
he slides up the front portion d d, vane and all, by which it can 
be raised to twelve feet in height, which is as much as can be taken 
at any one station; and thus the vane is elevated without sloping 
the staff, or any loss of time. In order to show the height of the 
vane when the front half of the staff is raised, the same scale of 
divisions is continued as before, but is placed on the back of the 
front piece, and is therefore invisible until the staff is drawn out. 
The divisions now proceed from the top downwards, and are 
marked for reading off by the top of the lower half of the staflf, 
the appearance of which, from behind, when raised, is shown at 
Fig. 93, in which e is the top of the lower staff, and/" the under 
part of the front staff, upon which the two scales of divisions are 
separated by the dovetailed channel ff, in which the projecting 
slider of the lower staff fits, as shown at g in Fig. 91, and in 
which h is a clamping screw, for fastening the two half staves to- 
gether at any elevation that may have been given to the front 
staff. The appearance of the back of the vane, its socket and 
spring for producing friction, are shown at k k, Fig. 93. 

319. In order to take levels, or use the instruments above de- 
scribed, the line intended to be levelled must first be selected 
and set out by picket-staves placed at equal distances asunder. 
This division in ordinary operations is done by steps or paces; 
but when great accuracy is required the distances are measured 
by the chain. , Supposing in the first instance that pacing will 
answer, a picket-staff is set up at the starting point, and the sur- 
veyor taking long and equal steps in the direction of the line 
moves 100 paces, and then sets up another staff. He proceeds 
in like manner setting up a staff, arrow, or some mark that may 
be easily distinguished and found again at every 100 paces for 
some distance. 100 paces is here taken as an example, but the 
distance between the marked points must depend upon the 
nature of the country and the object of the survey. If the coun- 
try is very flat, and it is only necessary to determine the relative 
altitude of the two extreme points of the survey, much longer 
distances may be taken between each mark; but if the country 
is hilly and uneven, it will be impossible to take distances even 
of 100 paces at once, but we must be satisfied with getting them 
50 or even 25 paces asunder, as will hereafter appear. If, like- 
wise, it is necessary to make a correct section or profile of the 
surface of the country by drawing or plotting it, the stations 



ON LEVELLING. 165 

must be short, because those points only that are marked or set 
off as stations will appear, or be given in the field book from 
which such drawing must be made. 

320. Presuming, however, that the country is tolerably level, 
and that the distances first named of 100 paces each will suffice, 
we will call the picket-rods or other markers that have been set 
up No. 1, 2, 3, 4, &c. No. 1 designating the first rod or start- 
ing point. The levelling instrument is first set up and adjusted 
as before described (314) so that its telescope may range all round 
in a truly horizontal direction at No. 2, turning the telescope 
towards No. 1, where a staff-bearer is stationed, and holds up 
the levelling-staff and vane in a vertical position with its front 
towards the telescope. The observer turns his telescope so as 
to get the staff in the centre of the field of view, and he now 
signals the staff-bearer to raise or depress the vane as may be ne- 
cessary, by making motions with his right hand, such as will 
indicate that the vane must be lowered if it is already too high, 
or to raise it should it be too low. The proper manner of mov- 
ing the vane, which saves much time, and is soon acquired by 
practice, after receiving the first signal that it is too high or 
too low, is to keep it in constant gradual motion in the direction 
in which it has to be moved, during which the observer keeps 
his eye constantly at the telescope, and as soon as he finds it is 
at the precise point, or very near to it, he throws his right arm 
out into a horizontal position, as a signal to the staff-bearer to 
stop moving. He now applies his eye again to the telescope, to 
see if the horizontal hair is precisely upon the middle of the 
white central line of the vane; if not, he signals for the vane to be 
raised or lowered, or stopped as before, when it is exactly in its 
right place. If the telescope has sufficient power, he reads the 
division on the staff that the cross-wire cuts, or if this cannot be 
done, he signals the staff-bearer that the operation is finished by 
taking off his hat, or any previously concerted signal, when the 
staff-bearer comes up to him, bringing his staff, and taking care 
that the position of the vane upon it is not altered. It is then read 
off and entered in the book, suppose it to be 3.25 if using the 
decimal side of the scale, or 3 feet 3 inches if using the inches. 
This is called a back observation, because the observer has been 
looking backwards towards mark No. 1, from whence the level- 
ling commenced. That done, the observer and instrument re- 
main stationary at No. 2, and the staff-bearer proceeds to No. 3, 
where he takes his station and holds up his staff with its face to- 
wards the telescope, which the observer in the mean time turns 
round into this new direction. Let it be supposed that the sta- 
tion No. 3 is so much down hill, that the observer on looking 



166 ON LEVELLING. 

through the telescope finds that it ranges over the top of the 
staff. He apprizes the staff-holder of this, by holding both his 
arms up over his head, indicating that both staves must be used. 
The staff-holder accordingly pushes up the vane until it touches 
the stop and stands at 6 feet, and then slides up the front rod 
until the observer apprizes him as before that the vane is 
brought to its proper elevation, and the observation is concluded. 
The staff-holder now in turn stands still, and the observer having 
finished at station No. 2, takes up his instrument and proceeds to 
No. 3, when he writes down the elevation of the vane in his 
book, and records this as a forward observation, because it is in 
the direction in which the survey is proceeding; suppose it to 
be 7.50 or 7 feet 6 inches. Having done this he proceeds to 
No. 4, where he plants and adjusts his instrument, and turns the 
telescope back towards No. 3, for another back observation. 
The staff-holder being apprized by signal that the instrument is 
adjusted, again holds up the staff at No. 3, on the precise spot 
where the last observation was taken, and having turned the face 
of the vane towards the telescope, awaits the signals of the ob- 
server, and moves his vane accordingly until he is apprized that 
it is in right position, when he leaves his post and proceeds 
onwards to the observei to have that position recorded, say 4.33, 
and that done, he goes to station No. 5, where he again holds up 
the staff, the telescope is turned to it, the vane adjusted as before, 
when the observer and instrument move onwards to set down 
the elevation and take up a new position at No. 6, and there the 
same operations are repeated. The process of levelling is there- 
fore very simple, and when the observer and staff-holder under- 
stand each other's motions the operation may be conducted with 
great expedition. The only delay that occurs is in the due ad- 
justment of the instrument, which requires great care and atten- 
tion, without which the whole operation is good for nothing. 
All the rest may be done at a running pace, and forms a health- 
ful and pleasant exercise in cold weather. 

321. The reason for taking the observations, as above describ- 
ed, by back and forward observations, will be apparent after what 
was said in explanation of a true level line (297) which was 
illustrated also by Fig. 82. If the observations were taken in the 
forward manner only, they would be subject to the errors then 
explained, or must be corrected by a troublesome operation at 
each station, because as distant objects are only seen in right lines, 
horizontal instead of level lines would be obtained. Thus re- 
ferring again to Fig. 82, suppose the levelling instrument is 
placed and adjusted at «, and that it is necessary to set out a 
level line towards e, that is, such a line as would serve for the 



ON LEVELLING. 167 

surface of a canal. On looking through the telescope our line of 
sight will be directed to h in a horizontal or apparent level di- 
rection, and the bottom of the ball d would appear to be level 
with a. But from principle this is known to be untruej and that 
we must measure and deduct the distance e d from the apparent, 
in order to obtain the true level, and this is the object of the staff 
and vane. Suppose the staff to be held up perpendicularly at e, 
and that d is its vane, which stands at five feet high. Then the 
foot of the staff at e instead of its vane d would give the level 
point. But the levelling instrument itself stands some height 
from the ground, say four feet, therefore the point a would not 
be level with e, but we must deduct the four feet from the five 
feet previously obtained, and this would bring the level point to 
one foot below d. But the point d exists only in empty space 
w^hen the vane is removed, and leaving nothing to mark its posi- 
tion, it becomes necessary to compare the position of e with a, and 
yet no direct data occur for making that comparison. We have 
obtained the result of one foot from the figures, but we cannot 
say that e is one foot higher or one foot lower than a, because 
we know it is exactly level. It can, therefore, only be so de- 
scribed in the book, and identified on the ground by driving a 
marking stake to denote it; and if the level has to be pursued 
further, the instrument may be placed over this spot, its height 
taken and a new point identified, an operation that will be found 
tedious, troublesome and liable to errors if attempted for a con- 
tinuous line, though it may be resorted to with advantage for 
proving work when finished or in progress in a manner that will 
be hereafter described. This operation is called Simple Level- 
ling. 

322. If, on the contrary, the process of back and forward sights 
at equal distances, or what is called compound levelling is adopted, 
the process is easy, simple, expeditious and free from errors if care- 
fully conducted. When the method of reducing the observations 
is explained, it will be found that the height obtained at a back or 
forward observation is to be deducted from that obtained in an 
opposite direction, so that these heights are thus compared togeth- 
er without any regard to the height of the instrument, and a result 
is at once obtained; for the horizontal lines of sight are, by this 
subtraction, converted into a curvilinear form corresponding with 
that of the earth. Thus again recurring to Fig. 82, suppose the 
instrument still adjusted at the point a just midway between e 
andy, and that the levelling is proceeding in a direction from J" 
towards e. Then turning the instrument towards /"would give 
a back ohservation. The vane staff is held up at /, and the dis- 
tance between /"and the line a c obtained, say five feet; the vane 



168 



ON LEVELLING. 



staff is then moved to e, and the telescope turned round for a for- 
ward sight, and the height from e to d measured, which suppose 
also to be five feet; this subtracted from the last result would 
leave no remainder, indicating that there is no difference between 
the level of the two points, or that they are on what is called a 
dead level. If, on the contrary, a hill or projection had existed 
atyj (as indicated in the figure,) the vane staff held upon it would 
have been reduced in length, say to three feet, and this being 
deducted from five feet at e, would indicate a difference of two 
feet between the top of the hill and the point e, or in other words 
that the point e was two feet nearer to the centre of the earth 
than the top of f. It thus appears, that to obtain the difference 
of level between two distant points, the height of the instru- 
ment need not be regarded or entered in the book; nor indeed 
is it essential that it should be in the line of the work. But if it 
is necessary to produce a drawing or profile of the surface of the 
country passed over, then the more points that are ascertained 
the more correct that profile will be; therefore it becomes ne- 
cessary to multiply the stations by taking them at short dis- 
tances apart. 

323. The process of taking levels by this method is so simple 
that nothing more need be said about it. except what will be de- 
veloped in explaining the field book, or book in which the seve- 
ral observations are recorded as before mentioned. 

The same form of book that is used for land surveying also 
answers for recording levels. The pages being ruled into three 
columns, of which the left hand contains an account of the back 
sights. The central one the stations of the levelling instrument, 
and the right hand, the forward sights; and these are not written, 
as in land surveying, from bottom to top of the page, but begin 
at the top as in common writing, as for example, 



324. xlccount of levels taken from the centre of Mr. 



gate, proceeding along the high road in an easterly direction to 
the ferry on the South river. — 28th August, 1837. 

Forward Sights. 

opposite large oak tree 

7.50 at run across road 
west end of barn 

3.61 E. corner of X lane 

opposite middle of stable 

3.51 two yards short of ><| fence 
opposite field gate on left 

3. 90 at a high poplar tree 



Back Sights. 

At centre M.'s crate 3.25 


Instrument 
stations. 


110 


paces, 


6.20 


1 o 


110 


jj 


3.42 


2 O 


110 


3J 


3.48 


3 O 


110 


J> 


- 


4 O 



3.36 



ON LEVELLING. 



169 



110 



110 



110 



55 



55 



J? 



}) 



>? 



?? 



>? 



4.12 



4.31 



4.02 



3.90 



Total 1600 paces. 



5 O 


6 O 


7 O 


8 O 


9 O 



4 yards beyond X fence 
3.31 at angle, and fence ends 

a stake driven, as no mark 
2.31 corner of small house 

at door of blacksmith's shop 
4.00 opposite door of ferry house 

corner of ferry house garden 
7.91 down beach (no mark) 

at the mooring post 
8.40 at edge of river 



325. The same kind of entry would be continued in the book 
until the entire line of levelling should be complete, but enough 
has been given to show the manner in which the book is kept; 
and very few observations will render the reasons of these en- 
tries, as well as the manner of using them, clear and intelligible. 
Referring to the explanation before given of the process of level- 
ling, the instrument is planted at a certain distance beyond the 
commencing point, a back sight is taken to that point, and this 
mark O is used to denote the station or place of the instrument. 
Accordingly the first entry in the book is 3.25 in the left hand 
column, which shows that this number was cut by the vane on 
the staff placed in the centre of M.'s gate, as viewed by the in- 
strument standing in its first station 1 O, which station is stated 
to be opposite to a large oak tree, the position of which is identi- 
fied by the 110 paces written to the left of that station, which 
shows its distance from the gate. 

The next entry is 750, at a brook or run across the road, 
and this is put in the right hand column, as being a forward 
sight, but no number is set against it to indicate its distance, be- 
cause the distances are always presumed to be equal, unless a 
special entry is made that they are not so. This run across the 
road is therefore 200 paces from M.'s gate, and the operation as 
far as it goes is complete, which is the case with every pair of 
sights, that is 1 back and 1 forward throughout the line; conse- 
quently, if we subtract 3.25 feet from 7.50 feet, 4.25 will re- 
main, and this is the difference of level between M.'s gate and 
the centre of the bottom of the run. But I wish to know 
whether this difference is so much higher or lower than the gate, 
to ascertain which I look to the entries to find which position has 
exposed the greatest quantity of measuring staff or given the 
highest number, because the more the staff has been exposed 
the greater must be the distance to the ground. I find the 
highest of the two numbers is a forward sight, or in the direction 
22 



170 ON LEVELLING. 

I am going, therefore I have gone down hill from M.'s gate 
to the run, and I find the ground falls 4.25 or 4 feet 3 inches 
in 220 paces. If, on the contrary, the high number had been a 
back sight, then I should have been ascending a hill which will 
occur in the next pair of sights. 

The next entry is 6.20 as a back sight, but no remark is made 
against this to denote its position, because none is necessary, for 
by the explanation previously given all the back sight stations 
after the first, must be on the precise spots from which the pre- 
vious forward sight was observed. The position, consequently, 
of 6.20 is identical with 7.50, which has been described. It is 
the levelling instrument that must move in this case, and accord- 
ingly we now find it at 2 O, opposite the west end of a barn, 
and 110 paces in advance of the sight vane, from which a back 
sight is taken giving the result 6.20 before referred to. This be- 
ing entered, its corresponding forward sight is taken at another 
110 paces in advance, being the E. corner of a cross lane, and 
the result is 3.61. This pair of numbers may be subtracted as 
before, and the remainder, 2.59, is the difference of level; and, as 
the high number is now among the back sights, I find I am 
working up hill, and that the land at the cross lane is 2.59 feet 
higher than that at the run. To ascertain what the height of the 
cross lane is, in respect to M.^s gate, I may subtract the 2.59 of 
this last operation from the 4.25 given by the first, and the re- 
mainder 1.66 shows me that there is that difference of level be- 
tween M.^s gate and the cross road, which last is the lowest by 
that quantity, or 1 foot 8 inches; and as this point is distant 4 
reaches of 110 paces each from the gate, that is the general fall 
of the land in 440 paces, or in so many yards or chains if those 
measures have been adopted instead of paces. 

326. There is, however, no occasion to go through the com- 
plicated process of subtraction just referred to, when we desire 
to compare the level of one spot with that of another, however 
near or distant, because in the same way that any one pair of 
sights will give the relative level of the points when they are 
taken, and the rise or fall of the country between them, so will 
the sums of any number of pairs subtracted from each other in 
like manner give the same result with much less trouble. Thus if 
instead of first finding the fall from M.'s gate to the run, and 
then the rise from the run to the cross road, we had taken the 
sum of the two back sights, viz: 3. 25 + 6. 20z=:9. 45, and that of the 
forward sights 7.50 + 3. 61^=11.11, and subtract these from each 
other, we should obtain the same result 1.66. In like manner, 
if we wish to know the difference in level between more distant 
points, it is only necessary to collect all the back sights into one 



ON LEVELLING. 171 

column and the forward ones into another, so that they may be 
separately added and subtracted, when the result w-ill be given; 
observing always to take the observations in pairs, that is, to have 
as many back sights in one column as there are forward ones in 
the other. Thus if I desire to know the difference in level be- 
tween M.'s gate at the commencement of the survey, and the 
forward sight of the 7th station opposite the door of the ferry 
house, which is 1540 paces distant, I must collect all the back 
observations into one column and the forward ones into another, 
add up the columns, subtract one sum from the other and the re- 
mainder will give the difference thus: 



Back sights. 


3.25 


6.20 


3.42 


3.48 


3.36 


4.12 


4.21 



Forvmrd sights. 
7.50 


3.61 


3.51 


3.90 


3.31 


2.31 


4.00 



28.14 28.14 

It happens in this case that the two sums are exactly equal, 
therefore if subtracted nothing would remain; and this shows that 
however undulating the country may have been between these 
two points, that they are exactly level with each other, but pro- 
ceeding onwards we have 

4.02 7.91 



. 90 8.40 



7.92 against 16.31 

7.92 



8.39 

Showing that from the ferry house to the river, there is a fall 
of 8. 39 feet in a distance of 220 paces, or four reaches of 55 paces 
each, because the fall is here so rapid that it could not be taken 
like the former part of the survey, in distances of 110 paces each. 

327. A field book kept as above described w^ill, therefore, with 
very little trouble, give the difference of any one single pair of 
observations; of the extreme ends of a line; of any portion of the 
same that may be required, or of each distinct portion of an entire 
line, however extensive it may be; and the operations of levelling, 
as above described, are constantly resorted to by the Engineer 
for determining the fall of rivers, for building mills, or other pur- 



172 ON LEVELLING. 

poses; for ascertaining the slope of hills; judging of the possibility 
of making navigable canals, or water-works for supplying towns 
with water, and many other purposes. 

328, The reason why the two last reaches in the above de- 
scribed survey were diminished down to 55 paces each, instead 
of 110, like those that preceded, is, that when the slopes are steep, 
the instruments of observation cannot command them, unless they 
should be made of such large dimensions as to height, as would 
destroy their portable character and render them unfit for practi- 
cal use. Thus if we suppose ab c de, Fig. 94, to represent the 
side of a hill that has to be levelled, and c to be the position of 
the instrument, fixed and adjusted, for taking the levels, which 
we will presume is part of a long line that is proceeding onwards 
in the contrary order of the letters, or from e towards a, and that 
e is the position in which the vane-staff was placed in the forward 
sight of the last observation, and where of course it must main- 
tain its position — on applying the eye to the telescope it will be 
discovered that the line ^^y is the horizontal or apparent level, 
in which it directs the sight. But that line cuts the hill dXf, and 
does not reach the staff e; consequently its divisions cannot be 
read, and as the staff e is fixed in position, no alternative exists 
but to move the levelling instrument higher up the hill or to d, 
so that instead of indicating the line of sight g f, it may indicate 
another parallel to the first, as shown by the dotted line above it, 
which, it will be perceived, cuts the vane-staff very near its bot- 
tom, but still high enough to permit a back sight to be measured 
and recorded. That done, the telescope is turned round for a 
forward observation, and if it had stood even in its former posi- 
tion c, the slope of the hill is so great that when the vane-staff 
should be set up at the place a measured off and assigned to it, 
(the distance a c being equal to c c,) the line of sight/"^ would 
pass quite over it, even though both staves should be drawn out 
to their utmost limit as at a; but as the instrument has been 
moved up to d the case will be still worse, and the vane-staff will 
not be visible until moved up to h, so that in hilly countries, or 
where rapid slopes exist, the extent of level that can be deter- 
mined by each pair of sights becomes very limited, and the work- 
ing is much more tedious and troublesome than in more level 
places. 

329. The most tedious and troublesome operation in the prac- 
tice of levelling, and one that requires the most strict attention, 
is the setting of the instrument truly level by the levelling screws 
of the parallel plates; and it is provoking after having taken this 
trouble to find that the instrument has been stationed in a place 
where it cannot be used, as in the case just described, but that it 



ON LEVELLING. 173 

has to be moved, and the whole operation repeated, which may 
happen more than once at a single station. To make sure of 
avoiding this repetition, the surveyor, therefore, often makes his 
sights unnecessarily short, and this again is not desirable, because 
the number of stations is thus augmented. It is with a view to 
remedy this inconvenience that the adjusting screw _§•, Fig. 87, is 
applied to all the best instruments, the effect of which, as before 
noticed, is to elevate or depress the Y m.arked d, by which the 
telescope may be almost instantly adjusted to level in any one di- 
rection, although it cannot be turned round. Whenever, there- 
fore, the surveyor is in a hilly or troublesome location, this screw 
should be resorted to for the purpose of selecting a position for 
placing his instrument, and by this means he will be able to take 
the utmost limit of distance at which he can fix his instrument, and 
proceed to its final adjustment as to level, without fear of having 
his labour thrown away: and having found the place of the instru- 
ment, he measures by paces or the chain, from that to the back 
sigh t-stafi* about to be observed, and sets out that same distance 
forwards, to obtain the position the vane-staff must be moved to 
for his next forward observation. In hilly countries, therefore, 
the line only, without the distances to observe from, can alone be 
staked out, and the distances so depending on local circumstances 
must be measured off, after the positions of the instrument are 
ascertained, instead of beforehand, as in other cases. 

330. In performing levelling operations, such as have been 
last described, it frequently happens from local circumstances 
that the distances of the back and forward sights cannot be made 
equal, or at any rate without much additional trouble. Thus in 
Fig. 94 the distances d e and d b are not equal. It is true they 
might be made so by shortening d b, and setting up the staff at c 
instead of b, and this should be done whenever great accuracy is 
required. But this would create additional trouble by making 
an additional station necessary in descending the hill, for now 
the levelling instrument must be set up at b to get an observation 
between c and a, while if the distance d b he. maintained, the in- 
strument mav be carried below a for the next observation; and 
in short distances there is so little difference between the appa- 
rent level, as indicated by the telescope, and the true one, that in 
all distances not exceeding ten or twelve yards, it maybe passed 
over without notice. Should the distance be greater it will be 
well to correct it by the table printed at the end of this chapter. 
Another method is frequently resorted to for producing this cor- 
rection, which is, that if it happens that one of the sights, whether 
forward or backward, is unavoidably much shorter than the other 
in one pair of observations, the sights in the next pair may be 



174 ON LEVELLING. 

made equally different, but in the contrary order. That is to say, 
if a very short forward sight succeeds a long back 'sight at one 
station of the level, an equally short back sight, and equally long 
forward sight may be taken at its next position. Thus suppose 
after traversing a nearly level country i k, Fig. 95, we arrive at 
at a hill Im which intercepts the view through the telescope of 
the level placed at k, and that h is the position in which the last 
vane-staff has been placed. If the levelling instrument had been 
placed in the valley at o, so as to be half way between c and the 
next vane-staff /, several sights might be necessary to carry the 
operation over the hill. In order, therefore, to save time it is 
placed at k, so high up the hill as to catch the bottom of the staff 
/, and the pair of sights is completed. It is evident, however, 
that the distance from i to k is much greater than from k to I; 
but the observer knows that from the form of the country he will 
be able to correct this, and accordingly he next stations his instru- 
ment at 771, so high up that he can see the staff / over the hill, 
and in doing this, he measures off the distance / tti equal to / ky 
and orders the forward staff to n, making the distance rn n equal 
to k i. By this arrangement the error that is introduced on one 
side into the observation taken between i and /, is compensated 
by an equal error on the other side between / and n, and the two 
errors thus neutralize and destroy each other. In difficult posi- 
tions, therefore, it will be seen that some skill is necessary for 
selecting a favourable position for the instrument, and this know- 
ledge can only be acquired by experience and the exercise of 
thought while conducting the operation. 

331. The process of compound levelling is so simple that it is 
presumed no farther explanation will be required of it. Going 
once over a line, in the manner described, will be sufficient in 
most cases for determining the possibility of constructing a canal, 
or selecting the ground for setting out a road. But if the work 
has to be actually carried into execution, it will be advisable, and, 
indeed, is necessary in many cases to prove the first work done. 
The proof of the accuracy of a levelling operation is generally ob- 
tained by going over the same ground again in an opposite direc- 
tion, that is, beginning the second examination where the first 
ended, and going back to where it began, to ascertain if the results 
tally in both cases; and in doing this it is not necessary to adhere 
to the stations before used, with the exception only of those that 
have to be compared together. When great accuracy is required 
it w\\\ be necessary to measure and set off the distances by the 
chain instead of trusting to paces, and when the ground is hilly 
to reduce the sloping measures to their horizontal value. (292.) 
The distance of the sights ought to be short, and the levelling 



ON LEVELLING. 175 

instrument to be in good order as to its permanent adjustments, 
(312,) while its local ones must be very carefully attended to. 
The stafif-holder should be very attentive to keeping the vane- 
staff quite upright while under observation, and always to place 
it on the same spot for a forward and back observation. If pos- 
sible, it is best to read the graduations on the staff by the tele- 
scope, instead of trusting the staff-holder to bring them up, as the 
vane may get altered, while conveying, without his knowledge; 
and for this reason the telescope should not invert objects. In 
very accurate work two vane-staves are used, by two staff-holders, 
at the same time, one being placed at the back and the other at 
the forward station, in order that the telescope may be turned 
backwards and forwards to them several times to make sure that 
no error of position exists; and when a portion of the line has been 
gone over twice and is proved and known to be correct, long and 
firm stakes should be driven into the ground at certain known 
and proved stations, and be entered in the book, to be referred 
to again in case of doubt, and to prevent the necessity of going 
over the whole line, should any error or omission be afterwards 
detected in the work. The staff-holder should never stand be- 
hind the vane-staff while under observation, but on one side of it, 
holding it by an extended arm. And on leaving off work in the 
evening, for meals, or other cause, always cease after taking a 
forward sig?it, with the vane-staff set upon some object that is im- 
movable, and may be recurred to again when the operation has 
to be proved or resumed. If no such mark exists on the spot, a 
stake must be firmly driven in it, for concluding upon. 

332. The next object of our attention must be to show how a 
drawing of a section, or profile of the country that has been level- 
led over, can be produced on paper from the minutes taken in 
the field book of the observations that have been made; such a 
drawing being absolutely necessary before the minute particulars 
of a road or canal can be decided upon, as well as for preparing 
the specification for the workmen, or the estimates of expense. 
This drawing, that it may show every thing distinctly, requires 
to be drawn to a large scale, and that usually adopted by Engi- 
neers is either eight or sixteen inches to the mile in length. This 
is large enough to show all necessary objects distinctly, and has 
the advantage, if eight inches is adopted, of having each furlong 
represented b}^ an inch, and each chain by the tenth of an inch, 
which quantities admit of easy measurement and computation. 
Sixteen inches is adopted when a larger scale is required, on ac- 
count of being double the former size, but this is usually denomi- 
nated the scale of five chains to an inch, instead of sixteen inches 
to a mile. Such large scales cause the drawings to become very 



176 ON LEVELLING. 

extended in length, because it is no uncommon thing to give from 
ten to twenty miles of section in a single drawing; and on the 
eight inch scale it would require eighty inches, or six feet eight 
inches of length of drawing to show only ten miles of section. Such 
drawings are consequently always made on several sheets of pa- 
per, pasted together laterally. 

333. However large the longitudinal scale may be, a moment's 
consideration will convince any one, that it will not be large 
enough for the vertical scale, or that which is to show the eleva- 
tions and depressions of a country, or the results of the levels 
taken, even if the largest scale, of five chains to an inch, should be 
adopted. The use of a section is to direct the Engineer in setting 
out his work, and the workmen in executing it, and should the 
construction be one in which water is concerned, as in forming a 
canal or water course, a foot or even six inches difference in height 
may make a material difference, and such quantity should, there- 
fore, be shown on the drawing. If, however, a chain or sixty-six 
feet is to be denoted by the fifth of an inch, as in the scale of six- 
teen inches to a mile, so small a quantity as the sixty-sixth part 
of the fifth of an inch would be almost invisible upon paper, or at 
any rate would not serve a workman to measure from; for the 
drawing representing a section of a country that only varied a 
few feet in level w^ould be little better than a line of unequal 
thickness. In order therefore to render a sectional drawing 
really useful, a much larger vertical scale is always used than 
that which belongs to horizontal distances, notwithstanding it 
has the effect of producing a very distorted representation, (if 
such it can be called,) of the thing it is meant to show, for it 
bears no similitude to it in form, although all the dimensions can 
be measured ofi' and calculated from with certainty and facility. 
The least space that can be taken with any certainty and utility 
to represent a vertical foot in the drawing is one-tenth of an inch, 
or ten feet to an inch, which is a scale of six thousand three hun- 
dred and thirty-six inches to a mile, and consequently is most 
enormously disproportionate to the lineal or horizontal scale; and 
yet however much larger that scale may be, vertical distances 
cannot be measured with certainty on a less scale than what has 
been mentioned, and a larger one is often adopted. 

334. The first step towards making a drawing of a section is 
to draw an accurate right line, with pencil, to represent the 
horizon; and the length of that line must depend upon the 
extent of country to be depicted, and the scale adopted for the 
purpose. Thus suppose it were desired to produce a section of 
the land recorded in the field book of levels given at page 168. 
The extent of the line of country to be represented must be ex- 



ON LEVELLING. 177 

tracted from the book and be cast up if the section is to be 
brought into a determined size, if not, and it is immaterial iiow 
long the plan may be, this will be unnecessary. In the present 
instance, to introduce the section into Plate III., Fig. 96, when 
there is but 6 inches of length to spare, the extent is limited. 
On looking to the entries it will be found there are seven stations 
or reaches, or pairs of observations each 220 paces long and two 
of 110 each, making a total of 1760 paces. But as the pace 
(although generally 30 inches) is no regular standard of measure, 
we may call these yards, and this shows the necessity of taking 
the distances in chains or yards, as before noticed, when a draw- 
ing has to be made from the entries. The 6 inches of line must 
therefore be divided into 16 equal parts, each of which will re- 
present 110 yards, or half a furlong. If, on the contrary, the 
space had not been limited, but the scale of 8 inches to a mile 
had been selected, the line drawn would have been 8 inches 
long, because the entire length is 1760 yards or an exact mile; 
or if the larger scale had been taken, this base line would be 16 
inches long. To determine its place upon the paper, look down 
the back and forward entries in the book to see in which column 
the largest numbers appear; because if they predominate in the 
forward column, the work is descending, and the line should be 
near the top of the drawing paper; but if the contrary, the sec- 
tion will be an ascending one, and the line should be made low, 
while on the contrary, if the numbers fluctuate and are occasion- 
ally high and low the line may be about the middle. Such a 
position will suit the line in the present instance, and according- 
ly draw the line p, Fig. 9Q, with a black-lead pencil, and 
divide it into 16 equal parts. Number every alternate one of 
these 1, 2, 3, 4, 5, 6 and 7, which numbers show the correspon- 
dence of these several points with the similar numbers of the 
instrument stations in the central column of the field book. The 
intermediate points under ab c d ajfand g shovy the positions 
of the back sight vane staves up to this point. By referring to 
the field book it will appear that after the pair of sights from 
station 7 the distances diminish to half their former lenjith, or to 
55 yards or paces; therefore subdivide the two remaining spaces, 
as at the numbers 8 and 9, which show the instrument stations, 
while A and i point out the positions of the two last forward 
vane staves. The line will now be laid out in exact proportion 
to the several lineal distances that have been measured upon the 
ground, and is now ready to receive the lines that are to mark 
the profile of the country. 

335. Before the profile lines can be laid down the vertical 
scale mu-st be decided upon, and placed at the end of the hori- 
23 



178 ON LEVELLING. 

zontal line, as at k I, making its zero or point at the line, and 
extending the scale as far as the profile lines will extend above 
and below it. If the horizontal line should be very long, it will 
be better to draw several of these vertical scales across it in 
different convenient places, in order to save the trouble of con- 
stantly recurring to the end, to take measurements. Suppose the 
scale of Yo of an inch to a foot should be adopted, then the ver- 
tical line must be divided into tenths of an inch as in the figure. 
Then calling or the commencement of the line M.^s house or 
the first back sight, and taking the back sight result 3.25 from 
the first forward sight 7. 50, as before done, 4.25 descending will 
mark the position of the ground under «, or at the foot of the 
first forward vane-staff. Accordingly take 4.25, or 4 feet 3 
inches in the compasses from the vertical scale k I, and transfer 
that distance below the horizontal pencil line under a, mark the 
point m so obtained, and ruling a line from io m will give a 
profile of the slope or inclination of the ground in that distance. 
As the next operation will be a comparison of the position of the 
staff at b with that just obtained, rule a pencil line n q through 
the point m parallel io o p and extending under b to measure 
from. Then take the pair of observations belonging to station 
2 from the book, viz: 6.20 — 3.61=2.59 working upwards. 
Therefore take 2.59 from the vertical scale and transfer it up- 
wards from the line n q directly under b, which will give the 
point ?i, which mark, and drawing a line from m io n will com- 
plete the section to b. Proceed as before, by drawing a pencil 
parallel line through r extending under c; and now on comparing 
the observations belonging to station 3 we have 3.51 — 3.42=0.09, 
or only 9 hundredths of a foot in a downward direction, because 
the forward quantity is the largest, but the quantity obtained being 
about 1^ inch, is so small as scarcely to admit of being perceptibly 
laid down by the scale used. Therefore the ground line, from r 
to under c, must be drawn very nearly level or parallel to o py 
and the pencil measuring line n may be continued as far as d, in 
order to set down the observations taken at station 4, which are 
3.90 — 3.48=0.42, or about 5 inches also downwards, and which 
must be transferred to the station under d. Through this point 
draw another horizontal measuring line to e, and obtain the result 
of station 5, viz: 3.36 — 3.31=0.05, which makes the section line, 
to be laid down from d to e, very nearly level, but rather inclining 
upwards. Station 6 gives 4.12 — 2.31=:1.S1 of elevation, which 
is laid down from iv to under^! Station 7 is 4.31 — 4.00=0.31 of 
elevation, which being drawn in from/" to ^brings the section to 
coincide exactly with the primitive horizontal line o py and shows 
that the point g is exactly level with the starting point at M.'s 



ON LEVELLING. 179 

gate, being the same result that was obtained by figures in the ex- 
ami^le worked on page (171), and affords a proof of the correct- 
ness of the sectional drawing. Continuing in the same manner 
to work station S we have 7.91 — 4.02=3.89, descending. This 
distance is accordingly set off under h, by dropping a perpen- 
dicular from the horizontal line o p d.t this point, and measuring 
the distance upon it to s, when the line ^^ is drawn. Through 
s draw another line, parallel to op, extending to the end of the 
line, for measuring off station 9, which, by the field book, gives 
8.40 — 3.90=4.50, descending, which set off from t to v, which 
is the surface of the water in the river, and drawing s v, will 
complete the section. Now draw a permanent horizontal line 
through V, parallel to p, until it intersects the perpendicular 
scale k I at /, continue that scale down to it, and raise perpen- 
diculars from the horizontal line to the curved surface, produced 
by the section at each of the points that had been previously 
marked or set off upon it, and that done, the pencil line j», with 
its marks and divisions and all the parallel measuring lines, may 
be rubbed out, as may also be all that portion of the vertical 
scale that is above 0, and then on writing in the distances, be- 
tween one point and another, on the horizontal line, or what will 
answer the same purjDOse, placing a horizontal scale under the 
figure, and writing any names or references to things or places 
on the surface, will complete the profile. 

336. It will be noticed in the above profile that all the lines 
that unite one given point with another, are right or straight, in 
which there may appear to be a want of accordance with nature, 
as a country is always gently undulating, instead of being com- 
posed of right lines and angles, as here represented. This is a 
fault that must be submitted to in compound levelling, and the 
only way of remedying it is to make the distances between the 
sight-vanes as short as possible, by which the right lines are 
broken into shorter lengths, and a nearer approximation to an 
undulating line is produced. No points are given in the survey 
except those on which the vane-staves, or levelling-rods, have 
been placed, but most surveyors occupy the left hand column of 
the levelling field book, in which but little is written, by making 
eye-sketches of the surface of the country, between one station 
and another; anjd in drawing the profile, these corrections and 
additions may be made, provided strict attention is paid to placing 
the ascertained or fixed points where they really occur. And in 
speaking of simple levelling, on which a few observations yet 
remain to be made, another and more correct method of rectify- 
ing these variations from truth will be pointed out. 

337. A section produced as just described, and as shown in 



180 ON LEVELLING.^ 

Fig. 96, is, nevertheless, of great utility. It is by means of such 
sections that the possibility of constructing a road, a rail-road, or 
a canal, can alone be judged of, or an approximate idea of its ex- 
pense be acquired. Thus, for example, suppose it should be 
desirable to construct a gradually sloping road from M.'s house 
at 0, to some point, as s, on the bank of the river, instead of the 
up and down hill surface that the profile exhibits, and we desire 
to look into the possibility and expense of doing so. In the first 
place the profile shows that the natural surface of the country, 
from r to w, is favourable to such a project, but the valley at m, 
is in the way. But, by supposing a line drawn from to r, it 
will complete a triangle o 7n r, the area of which may be deter- 
mined in square yards or feet, while its transverse measure, or 
the width of the intended road-way may be measured on the 
ground or determined in the mind, and this will furnish data for 
calculating the cubical quantity of soil necessary to fill up the 
valley. As a run of water exists at ?n, a brick culvert must be 
built to carry it off", and the expense of this must be taken into 
account. Next an impediment exists at iv, where the ground be- 
gins to rise; but setting out the direction of the desired road upon 
the section, by the line tv s, the section of the hill is reduced into 
an irregular trapezium wfg s, the area of which being found is 
multiplied by its breadth, and thus the entire quantity of earth 
to* be cut away is determined, and comparing that magnitude 
with the cavity or valley o m r, we ascertain at once whether 
this furnishes enough, or too much soil to fill it up. If too much, 
as will be the case in the present instance, we can then determine 
how much the valley must be filled up laterally, to cause it to 
take all the stuff', or we may determine that it will be better to 
give the road less slope, by carrying it out to a point higher up 
the bank than s, so as to take no more soil away than what shall 
exactly compensate or fill up the cavity without surplus. Having 
thus determined the number of cube yards of soil to be removed, 
the horizontal scale will show the distance it has to be carried, 
and this distance must be taken from 7 to a, because these are 
the average distances from which the soil must be taken and re- 
placed. By such data a very near estimate of the expense of the 
alteration may be made before the work is began. 

338. Let us next suppose that a country has been levelled from 
one river to another, with a view to ascertain the possibility, and 
form a rough estimate of the expense of constructing a navigable 
canal, and that the section from such levelling is prepared. The 
section will at once show the fall or difference of level from one 
river to tlie other. If the line turns out to be a continually de- 
scending one, and the upper river has abundance of water, no 



ON LEVELLING. 181 

difficulty will occur to the execution. B'eing in possession of 
the total fall, suppose forty-eight feet, the section must be searched, 
and will generally indicate advantageous places for building the 
locks, the sum of the depth of which must always be equal to the 
difference of level between the extremes, so that we may form 
some estimate of the number of locks and a pretty accurate one 
of the length and depth of cutting. If, on the contrary, the level 
presents considerable undulation, the line will not be a good one, 
because there must either be very considerable embankments to 
fill up the hollow places, or very deep and expensive excavations 
through such as are elevated. But when the section shows a 
gradually rising country, proceeding to a great height in the first 
instance, and afterwards falling down again to the other stream, 
a canal will be impracticable, unless a sufficient stream of water 
should be found in the higher regions to feed or supply both the 
descending branches; or the position of the canal should be deem- 
ed of sufficient importance to warrant the expense of erecting 
powerful steam-engines or other machines, for pumping up the 
water necessary to fill the canal and supply the two descending 
branches, which is actually done upon the summit level of the 
grand junction canal, between London and Liverpool. 

339. Enough has been said on the subject of compound level- 
ling to explain its simplicity and utility, and the chapter will, 
therefore, conclude with some observations on the use and appli- 
cation of simple levelling, or that in which the sights are taken 
by direct vision instead of by back and forward observation; for 
although this process is not applicable to long extended lines, it 
is, nevertheless, of great utility in many instances, especially in 
setting out work for execution, and the examination of its truth 
while in progress. When used in this manner, the object of the 
instrument is not to observe the difference of level between points, 
in order to their comparison, but to ascertain points that are ac- 
tually level in respect to each other, or how much they require 
to be raised or lowered in order to reduce them to true level. 
Thus, for example, if a long range of wall has been built, and it 
is requisite to examine its top range as to level, the usual mode 
of doing this is by the bricklayer's level, (300,) which, though 
commonly used in house or small work is, nevertheless, tedious 
and liable to error, when the length is considerable. Instead of 
using it, therefore, set up the levelling instrument at a distance 
in front of the wall, in such a position as will command a consi- 
derable range of the work, and elevate the stand of the instru- 
ment on a hill or other elevation, (natural or artificial,) to such 
height as will cause the telescope, when adjusted as for other 
levelling, to range over the top of the wall. That done, direct 
the telescope to the beginning of the wall, and place a staff- 



182 ON LEVELLING. 

holder upon it, with the staff and vane as usual. While looking 
through the telescope, cause him to elevate or depress the vane, 
until perfect apparent coincidence is produced between its central 
line and tlie horizontal hair of the telescope, after which the vane 
should not require to be moved or touched again, if the work is 
truly level; but he walks along the wall, setting down the staff 
upon it at every ten or fifteen feet, while the observer follows 
him with the telescope by turning it round upon its vertical axis, 
and if the wall is level, the wire of the telescope will cut the 
vane in every one of its positions, at the very same spot as it did 
in the first instance. But should it not be perfectly level, the 
vane will require to be raised or lowered by a quantity equal 
to the deficiency of level, which is thus shown at once by the 
scale of inches and parts. This operation, although described as 
being performed upon a wall, it will be self-evident, is equally 
applicable to any other extended construction that requires to be 
made truly level, as is the case with the rails of a rail-road, or 
the bottom of a navigable canal or its top banks, all of which are 
not only set out for finishing, after the first rough work has been 
performed, but are examined, as to perfection of level when finish- 
ed, by this process of single or simple levelling. 

340. In the setting out of a canal, rail-road, or other extended 
construction, simple levelling is constantly resorted to, after the 
compound operation has been finished, and the profile or section 
from it has been prepared. The one operation furnishes the grand 
outline of a plan, and the other comes in aid afterwards to fill up 
the minutiae. Thus in describing the section represented by Fig, 
96, it was objected that the profile lines, that join one given point 
to another, are all right lines; but should it be necessary to make 
this section a more accurate one, and to delineate all the little 
curvatures that exist on the ground between one station and an- 
other, recourse must be had to simple levelling to accomplish the 
object. Thus take any reach of the section, as from b to c, where 
the ground is nearly level or appears quite flat. To ascertain 
if it really is so, or how much it deviates from a flat surface, place 
the levelling instrument opposite to 3, but at a considerable dis- 
tance from one side or the other of the line before gone over, sup- 
pose, for example, one hundred yards out of the line, then adjust 
the instrument for a complete horizontal range. Divide the line 
to be examined into as many parts as it is desired to examine, 
equal or unequal is immaterial, provided their separate lengths, 
and the sum of their lengths be ascertained; set up a vane-staff 
upon one of the previously ascertained points at either end, and 
cause its vane to be shifted to such heiffht as will make it accord 
with the horizontal hair of the telescope. Having noted this 



ON LEVELLING. 183 

height down, cause the staff to be set up on each of the divisions 
or points to be examined, and the difference in height between 
this point so ascertained, and the others to which the vane must 
be shifted in its new positions, will give the elevation and de- 
pression of these several positions in respect to the first height 
obtained. Thus let h c, Fig. 97, be the portion of line to be ex- 
amined, the positions of the ends of which have been previously 
fixed as to elevation by the section, Fig. ^Q. The lateral position 
in which the levelling instrument is placed is 3, and the dotted lines 
that radiate from S io b d ef, Sac. show the directions in which 
the sights or observations are to be taken, by placing the vane- 
staff in succession on the points b d e, &c. It will thus be found, 
perhaps, that d is three inches lower than b, while c may be ten 
inches higher, and thus may a waving or irregular line be found 
out that will exactly represent all the minor inequalities of the 
country, and which can, of course, be introduced into the section 
if desired. Each reach of a long line can, of course, be submitted 
to this method of lateral examination and verification. 

341. Again, let it be supposed that the line 6 c is one hundred 
yards long, and that I desire to set out a fall for a rail-road or 
other purpose, of three inches or any small quantity in the one 
hundred yards, from b to c. This would be next to impossible 
by the bricklayer's or other forms of level, even though the sur- 
face of the ground might have been cleared and prepared for the 
purpose; but with a good levelling instrument it is easy and 
certain. Thus take a correct observation of the vane held at b, 
then slide the vane three inches up the staff and carry it to c, 
where, if necessary, a hole must be dug to receive its foot, which 
should be placed upon the top of a stake driven down until the 
vane is in accordance with the horizontal hair of the telescope, 
then digging out a right line from b to c, it will have the fall re- 
quired. In this, and all similar applications of lateral levelling, 
the position of the levelling instrument 3 must be as far removed 
from the points to be examined, as is consistent with distinct 
vision, in order to render all the lines of sight 3 b. 3 d, 3 e, 3 J^, 
&c., as equal as possible in length, because if they vary much, a 
compensation must be made for the dip or difference between the 
real and apparent level, as before spoken of; and for this same 
reason too large an extent in the direction b c should not be at- 
tempted, as more certain and correct results will be obtained by 
making the lines to be examined short, and increasing the num- 
ber of lateral stations of observation. 

342. Simple lateral levelling is not only used to prove and 
examine work, and set it out to given or required slopes, but 
also for the purpose of finding lines to be set out. Thus in the 



184 ON LEVELLING. 

example Fig. 96, if it is desired to find a better road to the river 
than the surface of the land indicates, and yet we do not wish to 
jDerform the earth work before referred to, it is probable such a 
one may be discovered by the use of the level. For the low 
point 77^ is a run of water that must have a fall or natural incli- 
nation, consequently the higher we trace that stream upwards, 
the greater will be the probability of finding land that may 
nearly agree with the desired line r in level, although it may 
be in a more circuitous route. Such search may be made by fix- 
ing the levelling instrument near r, with its telescope pointing 
up stream, while the vane-staff is applied to various parts of the 
surface; and, in like manner, we may search round the rising 
ground 2^y^ s, if it is in the nature of a detached hillock, to find 
a way round it that will be more level than going over it. 

343. As another instance, let it be supposed that the land re- 
presented by the plan Fig. 80, has been levelled, and a section 
made of it. That the crooked distance from C to V through f 
g and ^is two miles, and that the village V is six feet lower than 
C, and that this survey has been made with a view to determine 
whether a navigable cut can be made, or whether it will be bet- 
ter to construct a rail-road between the two places. A navigable 
canal requires to be perfectly level throughout its whole distance, 
unless locks are introduced, and then that the reaches between 
one lock and another should be level. If, therefore, a navigable 
cut is made of the height of C, its surface will be six feet out of, 
or above the ground at V, and it will require embankments on 
both sides during its whole extent. If, on the contrary, the 
height V is taken, its whole length will be excavation, and the 
side banks at C will be six feet perpendicular above the surface 
of the water, and in both cases it will be expensive, on account 
of the quantity of earth requiring to be moved. But by 
placing the levelling instrument in proper lateral positions, such 
as a, and beyond b g d e, &c., so as to take a succession of 
ranges, and having the vane-stafi* held at h and in different posi- 
tions along the line A c V, a series of points may be selected and 
marked with stakes, in such places that the first or nearest to C 
shall be three feet below C, and all the succeeding points level 
with it, so that at the end next V the last stake shall be only 
three feet above V. By this disposition, one half of the canal 
will be in excavation, and the remaining half in embankment, 
and the soil that is dug out of one end will serve to form the 
embankment at the other, without any inconvenient elevation or 
depression of the water, and with less expense and greater con- 
venience to tlie work than in either of the former plans. 

344. What has been said of a canal applies equally to a rail- 



ON LEVELLING. 185 

roadj as the level points along the brow of the hills will be found 
and marked out in the same manner. Or, if it is determined to 
give a certain slope or inclination to the road, it can be done with 
equal facility, by correctly ascertaining the entire length, and en- 
tire fall; then dividing the length into any convenient number 
of equal parts, and calculating what portion of that fall must be 
given to each part; and staking out the line upon the ground 
into a similar number of equal parts. The tops of those stakes must 
be set level by aid of the instrument, and having numbered them 
for reference, a specification may be made out for the workman, 
stating how much the work is to be below the top of each par- 
ticular stake. Or, what is still simpler and better, after the stakes 
have been levelled, the necessary portion may be sawed off the 
top of each of them, so as to reduce their tops to a parallel to the 
work that has to be executed. A parallel is mentioned instead 
of the real line, because that line is almost always on, or under 
the surface of the ground; and if the stakes were so placed, they 
could not be seen, or be conveniently cut off; but by making 
them all uniformly a foot, two feet, or any determined height 
above the work, they offer the advantage of having their tops 
exposed so that they may be boned, by looking along them to 
see that they range properly both as to height and to line, they 
are easily found, and the workmen work with equal facility; for by 
cutting a stick equal in length to the distance they are to work 
below the tops of the stakes, and applying it to any stake it in- 
forms them whether they are right or not. 

345. In using the levelling instrument for simple levels, it 
must be constantly borne in mind that as the observation is made 
in one direction only, without any thing to counteract it on the 
other side, the results will always be apparent instead of real le- 
vels. If, however, the radial lines of sight are pretty nearly of 
the same length, this will be of no importance, because the error 
that exists in any one observation will exist to an equal extent in 
all the others; and, therefore, will not effect the truth of the ob- 
servations. It was on this account that the position of the in- 
strument was directed to be as distant as possible from the ob- 
jects observed, and that too long a lateral extension should not 
be attempted from the same station of the instrument. Thus, in 
Fig. 97, the station 3 for observing points on the line b c is bad, 
because the lines of sight Sf and 3 e, are much shorter than 3 b 
and 3 c, and the longer the line of sight is from the point of ob- 
servation, the greater will be the difference between the true 
and apparent levels, as will be evident on inspection of Fig. 82, 
If, therefore, the line 3 c. Fig. 97, is twice as long as 3/, a com- 
pensation will be required to make 3 c accord with 3 /; for 
24 



186 ON LEVELLING. 

although the line h c may, in fact, be a true level, yet from this 
cause the two ends will appear a trifle lower than the middle. 
This is avoided in practice by taking the distance b c short, and 
the point of sight 3 at a distance from it, because that reduces the 
angular lines to nearly the same length. To have no error the 
plane of the line b c should be circular with the instrument in its 
centre, for then all the lines of sight would be equal radii. Such 
lines are, however, seldom met with in practice, but curved lines 
are very common, and w^e learn one lesson from the above prin- 
ciple, that whenever a curved line has to be examined as to level 
by this process, the instrument should never be stationed on the 
convex side of the curve, but always within its concavity, and 
as near to the centre of that concavity as can be estimated. 

346. It frequently happens that the Engineer or Surveyor is, 
from local or other circumstances, compelled to take long sights 
by simple levelling, or looking in one direction, or even to take 
long and short ones in the same direction, and that the compen- 
sation above referred to, has to be applied. As before noticed, 
when the distances are short, such as about 150 yards from the 
telescope, the difference between the real and apparent level is so 
small that it may be wholly disregarded; but when it exceeds 
twenty chains it begins to amount to more than half an inch, and 
must, therefore, be taken into account. 

347. The method of finding the difference between the true 
and apparent level at any given distance, is to square that dis- 
tance and divide the product by the mean diameter of the earth, 
when the quotient will be the difference required; for the differ- 
ence of the heights of the apparent levels, at different distances, 
are as the squares of those distances; consequently in short 
lengths the differences are very trifling, but increase rapidly as 
the distance increases. As, however, this rule is troublesome to 
work at the moment it may be wanted, the following table is 
calculated from it, and will show, on inspection, what allowance 
is to be made where the distance between the instrument and ob- 
ject observed are known. 



ON LEVELLING. 



187 



348. A TABLE 

Showing the quantity of curvature below the apparent level in 
inches, for every chain up to 100. 



o 




O 




O 




O 






Inches. 


>- 


hiches. 


>" 
a 


Inches. 




Inches. 










Co 

• 




s 

Co 




1 


0.0012 


14 


0.24 


27 


0.91 


40 


2.00 


2 


0.005 


15 


0.28 


28 


0.98 


45 


2.38 


3 


0.0112 


16 


0.32 


29 


1.05 


50 


3.12 


4 


0.002 


17 


0.36 


30 


1.12 


55 


3.78 


5 


0.003 


IS 


0.40 


31 


1.19 


60 


4.50 


6 


0.04 


19 


0.45 


32 


1.27 


Q5 


5.31 


7 


0.06 


20 


0.50 


33 


1.35 


70 


6.12 


8 


0.08 


21 


0.55 


34 


1.44 


75 


7.03 


9 


0.10 


22 


0.60 


35 


1.53 


80 


8.00 


10 


0.12 


23 


0.67 


36 


1.62 


85 


9.03 


11 


0.15 


24 


0.72 


37 


1.71 


90 


10.12 


12 


0.18 


25 


0.78 


38 


1.80 


95 


11.28 


13 


0.21 


26 


0.84 


39 


1.91 


100 


12.50 



ISS 



CHAPTER VI. 



ON EARTH- WORK OR EXCAVATION, EMBANKMENT, PUDDLING, &C. 

349. All the preceding chapters of this work have been de- 
voted to an account of the acquirements the young Engineer 
should make before he attempts to design, execute, or superin- 
tend work; and we have now to conduct him into the field, 
where the principles before taught will be called into action. In 
stating to him the various kinds of w^ork he will be called upon 
to execute, earth-work naturally presents itself as first in order. 
It being that which generally requires attention before any of 
his other operations can proceed. Among all the various mate- 
rials employed in building or the construction of machinery, 
timber is the only one that can be procured without penetrating 
into the soil; because stone, the materials for making bricks and 
mortar, slates, and all the metals are the produce of the earth. 
No building or fixed machine can be erected without first dig- 
ging and levelling its foundation. No road or rail-road for the 
conveyance of materials can exist without cutting and preparing 
the earth for its formation; and in the construction of navigable 
canals, or docks for shipping, it forms a leading feature of the 
whole operation. 

350. The mere digging or cutting into the earth, is so com- 
mon and obvious an operation that it may seem to require nei- 
ther skill nor explanation. This, however, only applies to small 

.and ordinary operations; for when the work is extensive, as in 
the formation of navigable canals, large reservoirs, tunnels, and 
the like, many expedients are resorted to that might not occur to 
the common workmen; they have arisen out of experience, and 
are only adopted because they economize labour and time, and 
consequently diminish the expense of executing the work. 

351. In populous countries, the mere mode of executing the 
W'ork is of little or no importance, either to the Engineer or his 
employer, his only duty being to set out the form of the work 
according to the plans previously prepared; and to sec that it is 
properly executed. The reason of this is, that in such places 



ON EARTH- WORK. 189 

workmen are usually to be found who will contract for the 
whole business, either at one specified sum of money, or for a 
certain price per cube yard, whatever the work may happen to 
measure; and in these cases such workmen hire and pay their 
labourers, find all the necessary tools and materials, and execute 
the work in such manner as they believe will render it most 
profitable to themselves. The Engineer, in this case, has no 
care or trouble about the execution, nor should he ever interfere 
in it, unless he perceives something palpably wrong. 

352. The usual course of proceeding, when contractors for 
work can be obtained, is for the Engineer to prepare his map or 
plan of the country, together with a correct profile or section to 
scale, of the intended work, and to write out a specification or 
particular explanatory of his drawings and plans, stating how 
the work is to be executed, where it is to begin, pointing out 
where the spare soil is to be deposited; when the work is to 
commence, what time will be allowed for its completion, how 
and where it is to be paid for; what penalty is expected to be 
incurred should the work be slighted, neglected, or not finished 
within the stated time; whether the contractor is to be kept free 
from water should springs be cut into in the progress of his ope- 
rations, or whether (as it is technically called) he is to bear his 
own water-charges, and any other particulars necessary to be 
known. These plans and particulars are then deposited in some 
accessible place, as near as possible to where the work is to be 
performed, or in a neighbouring town or city. Advertisements 
are then inserted in newspapers, or otherwise brought before the 
notice of the public, stating that certain works are required to be, 
done, the plans and particulars of which are deposited for inspec- 
tion and examination at a certain place, from some specified 
date to another, and inviting all persons who may be willing to 
contract for the execution of such work, to inspect the plans, 
or the ground itself, and to send in sealed tenders to a cer- 
tain place, on or before a certain day; in which they are to 
state the price and conditions upon which they will undertake 
the performance of the work. These tenders are opened by a 
committee, or some authorized person, and the common course is 
to let, or give the work to the lowest bidder. Notwithstanding 
this is the usual practice, it is one that ought not to be univer- 
sally adopted, because the ability of the contractor to perform 
the work, and his responsibility, ought always to be enquired 
into. Many instances occur in which parties, from the hope of 
gain, will put in tenders, without being acquainted with the nature 
of the work, and will take contracts for its performance at prices 
lower than it can possibly be done for, although they perhaps neither 



1 90 ON EARTH-WORK. 

possess the necessary implements, or capital to pay their men, or 
provide what is necessar}'^ for its execution; and, notwithstanding 
they may give sureties under bond for the due performance of 
what they undertake, yet when they find it costs more than they 
are to receive for it, or that their operations are so unsatisfactory 
to the Engineer that he will not pass their accounts for payment, 
abscond, leaving their sureties to suffer, or prove that they are not 
responsible; the Engineer has then to look out for other persons 
to finish his work, after much delay and vexation, and perhaps can 
only procure them at very advanced prices. The Engineer from 
his knowledge and experience, ought to be able to judge of the 
value of what he means to execute, and should be consulted as 
to the tenders before any one is accepted; and he ought not to 
permit any tender to be accepted when he knows the price offer- 
ed is such a one as will not allow the work to be executed in a 
good and substantial manner. Cases do sometimes occur, and 
the author has met with them, in which able and competent con- 
tractors having a heavy stock of materials and horses, and power- 
ful gangs of men, whose operations may have met with tempo- 
rary suspension from unavoidable causes, undertake to do jobs 
at very low prices through competition, rather than break up 
their establishments, and dispose of their stock; and in such rare 
cases, if the contractor is known to be capable and responsible, 
of course the Engineer is bound to give his employer the advan- 
tage arising from the circumstances; but in general he cannot be 
too careful about the character and responsibility of his contrac- 
tor. Persons who undertake large contracts for earth-work, as 
well as their workmen, have obtained the name of Navigators, 
from the circumstance of their work having in general some con- 
nexion with the formation of inland canals, docks and rivers or 
other accessories to navigation. 

353. It frequently happens that work may have to be executed 
in situations where contractors cannot be obtained, and then the 
Engineer has to provide his own materials, engage his own hands, 
and direct their operations, and the object of the present chapter 
is to give such directions as will enable him to do so to the 
greatest advantage. 

354. In all cases, whether contractors are employed or not, the 
Engineer is expected to set out his own work upon the ground 
for execution; so that the responsibilty of its form or shape rests 
upon himself. This setting out is performed by driving stakes 
at the corners or angles, and straining a line or cord from one 
stake to the other, to obtain right lines, which are afterwards 
marked by pegs or small stakes driven close to the line, before 
it is taken up to set out another length. Or what is much better. 



ON EARTH-WORK. 191 

the line may be marked either throughout its whole length, or at 
regular intervals, by what the workmen call nicking; which is 
merely using a common or straight-edged garden spade, by 
thrusting it into the ground about three inches deep, while held 
nearly perpendicular and close to the line while it remains on the 
ground; and then ineeting this cut by another in a more sloping di- 
rection about four inches from the first, so as to leave a small 
angular excavation in shape like the letter V two or three inches 
deep. Small stakes are often trodden down by cattle, removed 
through mischief, or hidden by grass, which occasions the trouble 
of re-setting out a line; while one that is nicked is not easily 
obliterated, and will remain visible for months after it is made. 
While nicking or even staking out a line, the cord used for set- 
ting it out, should be pegged to the ground after it is well adjust- 
ed, at every five or six feet by hooked pegs cut from the forks of 
neighbouring trees, in shape like Fig' 98, Plate IV. ^ in order to 
prevent its being deranged in position by wind, the spade, or 
other cause. 

355. When a square or right angle has to be set out on the 
ground, as in digging the foundations for square buildings, or for 
forming square ponds or reservoirs, it may be done by the sur- 
veyor's cross, or by a circumferentor or theodolite, first directed 
to a picket-stafi' placed in the direction of one line or side, and 
then on turning the instrument a quarter round or 90°, the posi- 
tion of a second stafi* will be obtained, and the summit of the 
angle will be at that point indicated by a plumbetlet fall from the 
centre of the instrument. The most usual method, however, of 
setting out right angles on the ground, is by an instrument usually 
possessed by workmen, or if not, that is easily made, called a 
ground square. It is merely two straight-edged strips of board 
about five or six feet long, the two ends of which are so united 
together as to form a right angle, as at Fig. 99, Plate IV., and 
they are held in that position by another similar strip nailed 
diagonally upon the other two, as shown in the figure. To ob- 
tain the right angle in making this implement, or to prove its 
correctness when made, use the process described at par. 34, 
substituting strained lines of thin cord for the lines there direct- 
ed to be drawn upon the paper. 

To use such a square for setting out a right angle, strain a 
line a h in the direction of one of the required sides. Fix the 
point where the right angle is to occur in that line, by driving 
a stake as at c, and fix another line to it. Then apply one side 
of the square close to, or parallel to the first line, letting the 
point of the square coincide with the stake; strain the other line 
close to the other side of the square, and fix its end to a stake d, 



192 ON EARTH-WORK. 

when the square may be removed, and the right angle indicated 
by the two lines may be staked or nicked on the ground. If a 
number of other angles differing from right angles have to be 
set out, similar implements to that described may be made for 
the purpose; but this will be unnecessary unless they are nume- 
rous. In general all angles that differ from right angles, are set 
out by the theodolite. 

356. If large arcs of circles, or curved lines nearly circular, 
have to be set out, one end of the line must be fixed to a stake to 
serve as a centre, and a sufficient quantity of line to represent the 
radius being let out, is held in the hand together with a pointed 
stake or large spike-nail, and being carried round the centre, 
the ground is scratched, or points are marked for placing pegs, 
when the curve may be nicked as before. Problems XIV., 
XV., and XIX, (pars. 74, 75, and 79,) are often resorted to for 
this purpose, using cords instead of drawing-lines, and erecting 
perpendiculars by the ground square. 

357. Whenever excavations are made for temporary purposes, 
and are to be filled in again, as in digging foundations for build- 
ings, or in the construction of drains, the sides of such excava- 
tion may be perpendicular; but such form will not answer for 
permanent operations that are to be exposed to the atmosphere, 
because, unless the soil is rock, or of a hard and imperishable na- 
ture, it will inevitably fall in to a greater or less extent, thus 
partly filling up the cavity that has been formed. In order, 
therefore, to make the sides of excavations permanent, especially 
if they are to hold water, it is necessary to slope or incline them 
to such an extent as will counteract this effect. No precise rule 
can be laid down for the quantity of slope to be given, as it va- 
ries materially with different soils; thus stiff or strong clay will 
stand when nearly perpendicular; stony gravel will generally 
stan-d at an angle of 45°; but loam that is readily soluble or 
rather miscible vvith water, and which contains a large propor- 
tion of sand, will hardly stand at any angle, and such soil is very 
abundant in the eastern parts of the states of New York, Mary- 
land, Delaware, and Virginia. 

358. Mathematicians would describe these slopes by saying 
that they made certain angles with the horizon; but such lan- 
guage is never used by workmen, nor would they, in general, 
know what it meant; the usual mode of designating slopes being, 
by a comparison of the sine of the angle with its base, or in other 
words the perpendicular height to which a slope reaches with a 
certain extent of horizontal base. Thus, for example, the slope 
produced by an angle of 45°, as shown at Fig. 100, Plate IV., 
would be called a slope of one to one, because any one distance 



ON EARTH-WORK. 193 

measured on the horizontal base ef, would be equal to the height 
of the perpendicular/"^; if, therefore, e f is one yard, /* ^ will 
be one yard also, and hence the expression one to one, which is 
but an abbreviation of the more extended one, that the slope rises 
one yard while passing over a horizontal extension of one yard. 
The next Fig. 101, shows a slope that would be called two to 
one, or two horizontal to one perpendicular, which is the case 
with an angle of 27° QQ'. An angle of 32i° produces a slope of 
one and a half to one. An angle of 18° produces a slope of three 
to one; and 13^° one of four to one; but as these angles are never 
mentioned in practice it is better to abide by the general rule, and, 
accordingly, in all future notice of slopes we shall de^signate them 
according to the usual practical method. 

359. The Engineer, after having examined the soil he has to 
work upon by sinking pits into it, or other means, must deter- 
mine the slopes he intends giving to his work, as these have to 
be considered and allowed for in setting out the work upon the 
ground. Two to one is the slope generally adopted for canal 
work, because the generality of soils will stand at this inclination; 
if the soil is stiff clay the slope may be made more steep, or steer, 
as workmen call it; while, on the contrary, if the ground is 
soft and loamy the slope will require to be more flat. 

360. In setting out new canals or roads for execution, the first 
thing attended to is the central line; that being the one that is al- 
ways ascertained by the process of levelling before described, 
and staked out accordingly. This line has now to be more mi- 
nutely attended to and marked out by an additional number of 
stakes, if necessary, and which should be at equal distances. 
That done, the width of the bottom of the canal may be set out 
by pegs, being small stakes intended to be taken up again, more 
or less distant from each other, according as the face of the coun- 
try is even or rugged. If the country is flat and level a pair of 
pegs at every second chain will be sufficient, but if otherwise they 
must be placed at every chain or even half chain. These pegs 
are placed parallel to the first or central line, and at equal distances 
on each side of it, that distance being half the proposed width of 
the canal. The depth of canal and extent of slope to be given to 
its side banks having been previously determined, the slope lines 
may next be set out by other two lines of permanent stakes, at 
such distance exterior to, but parallel to the lines of pegs, pro- 
vided the country is flat or level, but if not, the two exterior lines 
of slope stakes cannot be proceeded with until another process of 
levelling has been performed, called cross levelling, and which is 
generally done at the same time that these stakes are put in. This 
staking out is simple, but to render it more clear, let us suppose 

25 



194 ON EARTH-WORK. 

the canal to be executed is to be six feet deep to the top of its 
banks, that the bottom is to be twelve feet wide, and that the 
slopes on each side are to be two horizontal to one perpendicular. 
The slopes will then extend twice six feet horizontally, or the 
length on each side, from the pegs, will be twelve feet or four 
yards beyond the outside of them, making the distance from the 
central line of stakes to the outside line eighteen feet, for half the 
width of the canal at its top, or thirty-six feet for its entire width; 
and, as the water is usually a foot below the banks, its width will 
be diminished four feet, or made thirty-two feet. Thus let a b, 
Fig. 102, Plate IV. ^ represent the level surface of the country 
in which a canal is to be set out, and let c be one of the stakes 
that has been previously driven to mark the middle of the line. 
Then measure two equal distances d c^ d e, of six feet each, and 
mark them on each side of the central line by the pegs d and e. 
Next take e g and df, each equal to twelve feet, and set these off 
by the stakes atyand^, these two points will indicate the extreme 
edges of the canal, and no other setting out will be necessary, 
because the workmen are desired to commence their cutting aty 
and g, with slopes of two to one, until they reach the depth of 
six feet, when, of course, they can produce no other figure than/" 
g h i, which is the true transverse section of the canal proposed 
to be formed. 

361. In such simple cases as that just described, it will be ob- 
vious that the intermediate lines of pegs at d and e will be use- 
less, as the distances cyand eg, of eighteen feet each, can be set 
out at once; and, accordingly, the lines of pegs are never used, but 
they were supposed in the present case to render the reasons of 
the operations more obvious, and must occasionally be resorted to 
in more intricate work. 

362. Let us next suppose that the surface of the land upon 
which the canal is to be set out, is on the side of a hill, or slopes 
instead of being level, as at A: / in Fig. 103, then the directions 
above given will not apply, because if we still conceive c to be 
one of the line of central stakes, and attempt to set out the ex- 
treme sides or slopes as before, by lines of eighteen feet long on 
each side of that central stake, one side stake will come at o and 
the other at jf?, and will not accord with the form to be produced; 
since, owing to the rise of the ground k /, the right hand slope 
will not appear at the surface at o, but will become extended to 
TUf and the left hand slope instead of being Rip will be contract- 
ed to n; consequently the left hand distance c n to he set out is 
much shorter than c in. The distance oiin from the water will 
also be much greater than before, and the side n will not be high 



ON EARTH- WORK. 195 

enough to contain the water; consequently the lower side will 
require to be raised by an embankment n q r k, built upon the 
natural surface k n, and formed out of a part of the earth taken 
out of the excavation, the section of which, in this case, will be re- 
presented by the figure n m s t. Now the form of this figure, and 
the quantity of excavation and embankment necessary to form it, 
cannot be ascertained until we are in possession of the level or 
horizontal line s t, or its parallel q v, and this can only be ob- 
tained by levelling. The process of simple or direct levelling 
is the one resorted to, and the result is called cross levelling, be- 
cause it is taking levels across or at right angles to the principal 
line as set out. It is performed by setting the levelling instru- 
ment adjusted over the first central stake, and directing its tele- 
scope in the direction of this row of stakes, when several cross 
levels may be taken without changing its position. The vane- 
staff is held upon the first central stake, suppose c in Fig. 102, 
and its vane moved up or down until brought to its proper 
coincidence with the horizontal hair of the telescope. The 
staff is then placed first on the stake g, and afterwards on f, 
and, if the vane requires no alteration of elevation, it shows 
that the three points e f and g, are on the same level, and that 
the sectional figure, as set out, is correct. 

363. Let us suppose Fig. 103 to be the position of things at 
the next stake in advance. The instrument retains its position 
without any other alteration than a new adjustment of the object- 
glass as to focus, on account of the increased distance of the 
second stake. The vane-staff is held on c, and its vane adjusted 
to height as before. It is then placed on the side bank peg o, 
eighteen feet to the right of c, and now its vane will be found too 
high, and must be lowered by a quantity equal to the distance o 
V, which is noted down. Then being placed on ^eighteen feet, 
to the left hand of c, its vane will require to be raised a distance 
equal top q, which is also noted down; and these distances ob- 
tained afford sufficient data for drawing or projecting a figure to 
scale, like that given on the plate; and from the scale, which 
ought to be at least half an inch to a foot, the positions of the 
several points are measured off and transferred to the ground. 
This, it will be perceived, is rather a rough mechanical approxi- 
mation to the form, than obtaining it by correct mathematical 
rules which would give it with precision. But the operation 
would require much more time, and would not be understood by 
workmen, who, when accustomed to their business, will frequently 
be able to set out a slope by the head, without paper, lines, or 
figures, if the difference in level is given to them, and at all events 



196 ON EARTH-WORK. 

the process is sufficiently accurate to answer all practical pur- 
poses. 

364. If the stake c is in the regular level line of the canal, 
the projection as above described will be correct, but if it is 
above or below that line, then any quantity that it is above must 
be subtracted from the length o v and added to p q, and if it is 
below, the contrary order of proceeding must be observed. 

365. It may be imagined that the next central stake in succes- 
sion, occurs on the summit of protuberant or rising-ground like 
zu c Xy Fig. 104. Then when the vane-staff is held on the out- 
side stakes, the vane will have to be raised in both positions, in- 
dicating that an embankment m.ust be formed on both sides of 
the canal, unless the central stake c is so much above the general 
run of level as to render this unnecessary. 

366. The central stake may happen to be so low, that not only 
the two sides require to be raised wholly by embankment, but 
this may be necessary even for the bottom of the canal itself; the 
canal is then said to be wholly in embankment. For while ex- 
cavation is the digging out and removing of earth, embankment 
is the placing or piling it up where it did not exist before, so that 
the filling up a hollow place to render it level, is a species of em- 
bankment, although the term is more usually applied to the rais- 
ing banks or projections of earth in places where they did not 
before exist. 

' 367. From the foregoing account, it will be apparent that 
although the central line of stakes by which a road or canal has 
been set out must be regular, and will have symmetry, this can 
never be the case with the exterior or side bank stakes, which 
must always stand in irregular or zig-zag lines unless they are 
on perfectly level ground, notwithstanding which the work set 
out by them will be straight and regular when finished and 
brought to one uniform height. Indeed the face of a country is 
often so altered by the excavations and embankments of large 
public works, that its inhabitants scarcely know it, and the En- 
gineer himself would frequently be puzzled in the measurement 
of the work done, from his inability to distinguish between its 
former state and the recent alterations, were not certain marks 
made and left for this purpose. It is on this account that certain 
conical masses, with grass and stakes on their tops, are generally 
found standing in the middle of canals, reservoirs and other ex- 
cavations, particularly in uneven countries, in form like y in Fig. 
104. They are called bench-marks by the Engineer, and very 
frequently old men by the workmen. Their use is to mark the 
position as to the elevation of the soil before it was touched, for 
they are not built up but consist of some of the former soil left 



ON EARTH-WORK. 197 

standing by digging the earth away around them. The grass 
growing upon them is the grass of the original surface, which, 
having been untouched, continues to vegetate, and prevents any 
deception being practised as to the actual former height of the 
soil when the quantity of excavation is measured after its com- 
pletion. 

368. These little hillocks likewise serve to preserve the posi- 
tions of the central line of stakes by which the work has been 
set out, for they are constantly left around those stakes, or round 
every second or third, as may be necessary; so as to give the 
Engineer an opportunity of levelling at any future time from the 
original centre stakes, or measuring distances from them to the 
side banks, or taking the depth of the cutting. And they are 
never removed until the work has been measured, and is in such 
a state of forwardness as to render their longer continuance 
useless. 

369. It sometimes happens that the cutting or excavation for 
a road or canal is very deep, and wide at the top, as when a hill 
has to be passed through; and in that case these bench marks 
cannot be left, for their base would of necessity be so large as to 
block up all the lower part of the work; in such places they are 
unnecessary, because whenever the side banks rise considerably 
above the work, they form the best marks that can be obtained, 
because a line can be stretched from one side to the other to 
measure from. If any hollow or protuberance in the natural 
ground exists, either on a hill or any other place that has to be 
cut through, it ought to be measured and ascertained by simple 
levelling or other means, before the work is began, since it may 
make a considerable addition to, or abstraction from the quantity 
of earth to be removed, and is frequently a source of dispute 
with workmen. 

370. It has been stated, that when the extreme sides or lines 
of a canal or other excavation has been set out, nothing more is 
necessary in order to produce the figure or form required, than 
to desire the workmen to proceed and carry down the slopes 
with an inclination of two to one, or any other degree of slope 
that may have been previously arranged; but it may not be 
obvious how the necessary correctness of slope is to be obtained 
and preserved. This is done mechanically by means of an imple- 
ment called a bevil plumb rule, and cannot be effected with 
any degree of certainty without it. 

371. The bevil plumb rule is shown at Fig. 105, Plate IV., 
and consists of three strips of board, a h and c, framed together 
in the form of a triangle, the piece a being a common plumb 
rule and plumbet, such as is used by bricklayers, and which 



198 ON EARTH-WORK. 

being held upright, the piece c is so fixed as to represent the 
slope required for the bank, and h is merely a brace for retaining 
the other two pieces in their proper angular position, and there- 
fore need not make a right angle with «, though it will be better 
that it should do so, because the implement then becomes useful 
for other purposes, for it may be used as a ground square, Fig* 
99, (355,) and by having a large hole for the bob to play in at 
each end of the plumb rule, the instrument may be reversed by 
making h the bottom rail, and then it becomes a useful level for 
trying the bottom or other level parts of the cutting. The 
sloping side c, ought to be at least three feet long; and separate 
instruments of this description will be necessary for each parti- 
cular slope, if more than one should be adopted in the work. 
Having such an instrument, there will be no difficulty in giving 
the necessary slope to the banks. Thus in Fig. 102, suppose g 
to be the exterior stake at which the slope is to terminate. The 
workman begins by opening a hole of about a foot or eighteen 
inches wide between e and g^ taking care to give sufficient slope 
to the side g i; when sufficiently deep, say a foot or two, the 
lower point of the bevil plumb rule is introduced into this hole, 
and its side c is brought into contact with the slope g 2, and then 
if the plumbet on the rule coincides with the line upon it, the 
slope is right: if not, it must be altered until this accordance 
does take place. That done, another similar hole is opened at 
the next outer stake, a few yards in advance, and is proved and 
adjusted in like manner, when the intermediate earth may be 
boldly taken away, until the excavation approaches very closely 
to the lines so set out, and when that is the case, more care and 
caution are required to pare away the earth in exact accordance 
with them, and the bevil rule is frequently applied to ascertain 
that the work is correct. 

372. By the same process the slopes are set out and adjusted 
on the other side, and throughout the length of canal; and a simi- 
lar principle is frequently adopted for setting out and working 
sloping roads, when it is known how much the road is to rise or 
fall in a given length. For this purpose, an instrument like the 
bricklayer's level. Fig. 84, is used, except that instead of making 
its bottom edge at right angles to the plumbet, it is made to 
slope or incline in the necessary degree. It is not, however, 
worth while to prepare such an implement, unless the slope has 
to be continued a long distance without any alteration, 

373. Excavation is always called cutting, or shifting soil, by 
workmen, and is measured and paid for by the cube yard worked 
decimally. The most convenient instrument, not only for setting 
out road or canal work; but for measuring it when finished, or in 



ON EARTH-WORK. 199 

progress, is the rolling pocket tape, which, for this purpose, should 
be divided into feet and inches on one side, and into yards, divi- 
ded into hundredths, and numbered at every tenth division, on 
the other. Such tapes are fitted up in leather cases, with a brass 
winch to wind them by, and a ring to pass the finger through 
and hold the tape at its extreme end. The ring counts into the 
measurement, and in using the tape the Engineer should retain 
the box in his hand, and give the ring to his assistant to hold 
against the point to be measured from, by which means he has 
the figures that give the result of the measurement constantly 
under his eye. The measuring tape is a most useful implement 
to the Engineer in many of his operations, and as the tape soon 
wears out by use, while the leather box and winch are durable, 
every Engineer should know how to prepare his own tapes for 
renewal. The best and strongest thread tape, (not cotton,) should 
be procured, half an inch or five-eighths wide. This should be 
tightly stretched in long lengths between poles in the open air, 
in which position it is painted on both sides with white lead 
ground in oil, such as is used for house-painting, and left until 
it gets quite dry. It is then brought in and laid upon a long 
table for division by scale and compasses, and the divisions being 
marked in pencil, are afterwards finally put in with black oil 
paint, used with a pen made of a dry reed. The large divisions, 
such as feet, yards, &c. are usually marked with vermilion 
ground in oil, in order that they may be more distinctly seen. 
A tape so prepared will last a long time, and may be washed; 
while many of those that are sold, have the divisions marked 
with common writing ink, and are obliterated the first time the 
tape gets wet. 

374. In measuring excavation, it is the hole produced or made 
in the ground that is the subject of measurement, and not the 
finished work, or soil taken out. Thus if the excavation is made 
on level ground, as in the example shown by Fig. 102, the 
whole canal would be in excavation, and the trapezoid f g h i 
would have to be measured by Prob. XXXI. (174); and, according 
to the dimensions before assigned to the canal, viz: twelve yards 
wide at top, four yards wide at bottom, and two yards deep, we 
should have eight yards for a mean width to multiply, by two 
yards deep, and the product sixteen would be the number of 
superficial yards in the figure; and that multiplied by the length 
or extent of the canal while the cutting continues of the same 
dimensions, will give the number of cubic yards excavated. 

375. Inthenextreachof the canal, the natural slope of the ground 
has transformed the shape of the cutting from its former figure 
into the irregular trapezium 7i m s t, Fig. 103, which must be 



200 ON EARTH-WORK. 

measured by the rule laid down in Prob. XXXII. (175,) while in 
Fig. 104 we have a figure of five sides, formed by the bottom of 
the canal, its two side banks, and the two sloping surface lines 
w c and c x; and where the shortest process will be to measure the 
entire canal or trapezoid, and deduct the two triangular portions 
formed by the top horizontal line, the two upper extremes of the 
sloping sides, and the surface lines w c and c x. These examples 
will not only be sufficient to show the manner in which the 
measurements are conducted, but likewise the importance of re- 
taining bench marks, and any other marks that will indicate 
where the precise position of the surface was before it was alter- 
ed. They likewise serve to show another important point, viz: 
that while every portion of the excavation is measured and paid 
for, embankment costs nothing unless the soil necessary for 
its formation has to be dug for that express purpose. The reason 
of this is sufficiently evident, because whenever a piece of exca- 
vation has to be performed, it is the duty of the Engineer to 
point out and fix a place in which the spare soil, coming out of 
it, shall be deposited, and it is the duty of the workmen to carry 
it to that place. If, therefore, the Engineer wants an embankment 
formed within a reasonable distance from the excavation, he has 
only to stake out or mark its position, and direct the soil to be 
deposited there, and the embankment is of course formed. But 
if the quantity of soil yielded by the excavation is not sufficient 
to finish it, and an additional quantity has to be dug from another 
place to complete it, that of course constitutes another excavation, 
and must be paid for accordingl}^. 

376. Notwithstanding an embankment may in many cases be 
formed without expense, still it generally happens that some addi- 
tional labour or care has to be bestowed upon the work, for which a 
remuneration is always allowed. Thus all removal of soil is paid 
for according to the distance it is carried, and if that distance 
should be increased by forming an embankment, instead of throw- 
ing the earth at the sides of the work as it proceeds, this would 
constitute a fair item of charge. Again, many soils used to form 
embankments, (particularly if they are to stand against water,) 
require to be laid in regular layers or strata, and to be rammed or 
pounded, or punned, as the workmen call it, in order to break 
the lumps, and make the work more solid and compact, and this 
is an additional charge. The punning is performed by wooden 
rammers, hooped with iron to prevent their splitting, and work- 
ed by men, and when adopted, the courses of earth should never 
exceed nine inches in thickness, otherwise the blows of the ram- 
mer will have little or no effect on the under part of the stratum; 
and, whether the operation of punning is performed or not, it is 



ON EARTH- WORK. 201 

impossible for the workmen to wheel and deliver the soil on to 
an embankment with the same nicety and precision as to form, 
as can be obtained in excavating soil from the earth. All em- 
bankments therefore must be rugged and uneven when first form- 
ed, and they require what is called trimming to reduce them to 
handsome, even and fair surfaces. The trimming consists of fill- 
ing up hollows and cutting off protuberances, and this accordingly 
is charged separately, at a price agreed upon and regulated by the 
superficial measure of the surface of the embankment instead of 
its solid contents. The same kind of trimming takes place upon 
the surface of all excavations, but it is never made a separate 
charge, being included in the price for doing the work and con- 
sidered as a necessary finish to it. 

377. The next object of consideration must be the method of 
performing the work of excavation, and the tools and imple- 
ments necessary for its execution. The first thing to be done is 
the loosening and detaching the soil from its natural position, in 
order that it may be taken up by a shovel and placed in a wheel- 
barrow or cart for removal. And this is done by that well known 
implement the pick-axe, made of iron with two points of steel 
welded on to it, and bent into the form shown at Fig. 106. For 
ordinary excavation it should be double-ended with an equal 
quantity of metal in each end, that it may balance well in the 
hand. Two feet, from point to point, is considered the most con- 
venient length, and the metal should not w^eigh more than ten or 
twelve pounds; if heavier, it fatigues the workman without an 
equivalent advantage in work, and most men prefer this tool 
chisel-pointed and about an inch wide, instead of being quite 
sharp. The common fault in pick-axes as usually made, is a 
want of sufficient depth and strength in the eye or socket through 
which the wooden handle passes, for in this place they usually 
fail or break. The side-plates that form the eye, ought not only 
to be thick for strength, but should be at least three and a half or 
four inches from d to e, in order to admit of the handle being 
well fixed, for the operation of this tool is a wrenching one, and 
unless this construction is attended to, the handles are constantly 
breaking or getting loose, which proves very troublesome. Pick- 
axes constantly require sharpening and repairing, if therefore 
there is no blacksmith in the immediate vicinity of the work, 
a portable forge on wheels should be provided to accompany it, 
and such are made in a very convenient form for the cavalry and 
engineering purposes of the army. 

378. The shovel most approved is what is called heart-shaped, 
as shown at Fig. 107, instead of straight edged, though some of 
both sorts are useful; they are generally used with a long handle, 

26 



202 ON EARTH-WORK. 

but occasionally the crook handle, as shown in the figure, is re- 
quired, and is stronger and cheaper than the usual form. For 
actual digging upon the surface, particularly in clay or soft ground, 
a scoop tool, of the form shown at J^ig. 108, is preferred. It is 
made like a common garden spade bent into a curved form, 
and in using it, it is advantageous to have a tub, or puddle of 
water formed, into which the tool i§ frequently dipped, to prevent 
stiflf clay or loam from sticking in the hollow of the scoop. An 
iron plate, called a guard, is rivetted on to a leather strap that 
buckles under the foot used with the spade, to protect both the 
foot and shoe, while urging the spade by that means into the 
ground. 

379. The ordinary process of digging consists in loosening the 
soil upon the surface, and taking it up by single shovel or spades 
full, which navigators call under-hand working, but they adopt 
a more expeditious method of proceeding, called under-cutting, 
by which much labour is saved. The first hole or opening must 
be made in the ordinary manner, but instead of working on the 
surface and digging over it one spade deep, and then beginning, 
and taking another spade's depth, they go to the full depth of the 
work, provided it is not more than six or seven feet; taking 
care to form the sides to their intended slopes, but keeping the 
front or side, on which the excavation is to proceed, nearly per- 
pendicular, or without any slope at all. The bottom of the hole 
being levelled and tried, the lower part of this front or breast, 
as they call it, is undermined or dug away by the pickaxe and 
shovel, to about a foot from the bottom, keeping the bottom as 
level and as nearly in its proper range as possible. The side 
slopes are treated in the same manner, or worked into the front 
about the same depth, the consequence of which is that a large 
mass of the earth of the front remains without any other support 
than that which it derives from its cohesion or adhesion to the 
earth behind it; and large masses, therefore, first crack or sepa- 
rate and fall. If they do not separate as readily as the workmen 
wish, two or three large wooden wedges, shod with iron, are car- 
ried to the surface, and being placed a foot or two behind the 
front or breast, are struck with heavy wooden mauls, and this never 
fails to detach large masses of the soil, which, by the concussion of 
their fall, are broken into pieces sufficiently small to be taken up 
into the barrows for removal. This, though an expeditious pro- 
cess, is one that is attended with some danger to the workmen; 
and therefore requires to be conducted with care. For the cracks 
or fissures that always precede the detachment of a mass of soil, 
are sometimes unseen or unheeded by the workmen, and masses 
fall when they are not expected to do so, and crush or maim the 



ON EARTH-WORK. 203 

men beneath. On this account a front or breast, of more than 
about six feet, should not be so worked; but, when the work is 
deep, the upper breast may be kept four or five yards in advance 
of the lower one, with a flat surface between, for the soil to fall 
upon, and deep cutting is almost always so conducted. 

380. The common form of wheel-barrows, with boarded sides, 
will not answer at all for the work of excavation. Such bar- 
rows being too heavy in themselves, and very inconvenient for 
inverting to discharge the soil. The best form, and that con- 
stantly used in England for this work, is shown sX Fig, 109; it 
is very shallow, not exceeding six inches in depth, its four sides 
splay open, or make angles of about 45° with the bottom, in con- 
sequence of which the soil is very easily discharged from it; but 
its principal advantage is in the shortness of the axis of the wheel, 
(which should be of cast iron,) which allows a facility of turning 
out the contents that cannot be obtained if the axis is long. 
Fig. 110, shows the manner in which the frame of the barrow is 
constructed, by morticing three cross bars strongly into the two 
side rails which form the handles, and come so close together at 
their opposite ends, as just to admit the wheel between them. 
The box of the barrow is separately made and fixed on to its 
place, as indicated by dotted lines in the figure, by screw bolts, 
with nuts underneath; and, as the box soon wears out by use, one 
frame will last for several successive boxes. The pivots of the 
wheel run in iron eyes, fixed by screw bolts under the rails, so 
that they, likewise, can be removed when worn out. A barrow 
of this kind, shallow as it may appear, will contain quite as much 
soil, when heaped up, as a man can convey with convenience, 
when working throughout the day. And the mere frame of the 
barrow, without its box, is very useful for conveying flat building 
stones, or short pieces of timber, that will lie on it with conve- 
nience. 

381. The barrows are never wheeled upon the ground, but 
three inch yellow pine planks of the usual width are used to 
form level tracks or inclined planes to run them upon; and for 
this purpose, when the plank, or one or both of its ends cannot 
rest upon the ground, they are propped or raised to the required 
height and inclination by blocks or a kind of stool with long 
legs, called tressels or horses. Planks of about twenty feet long 
are preferred when they can be used, not only to obviate a fre- 
quent repetition of joints, but because they are more easily fixed 
and supported. The bearings should not, however, be too dis- 
tant, because a plank should not spring or vibrate while the load- 
ed barrow is running upon it. If it does so, it should be propped 
or blocked up in its central part. The slopes or inclined planes. 



204 ON EARTH-WORK, 

formed of wheeling planks, should likewise be made as flat as 
possible, for it fatigues the workman less to run a greater dis- 
tance on a gentle slope, than a short distance on one that is steep. 
382. The usual distribution of hands in shifting earth is to 
employ two at the immediate excavation, to dig and fill; that is 
to say, one with a pick-axe to loosen and break down the soil, 
and the other with a shovel to fill a wheel-barrow that stands 
upon the end of a wheeling plank close to the work. That done, 
a third man carries away the loaded barrow, and takes it what 
is called a stage, being a certain distance along the wheeling 
planks. He is then met by another man who is wheeling upon 
the next stage, and a change of barrows here takes place. The 
second man proceeds onwards with the loaded barrow, and the 
first m^an returns to the excavation with the empty one he has 
just received from the second man. By the time he reaches the 
excavators, a second barrow, previously left there, is filled, and 
he therefore drops the empty barrow to be refilled, and returns 
back with that which is loaded. A stage in wheeling is always 
considered as twenty yards, when no specific agreement is made 
with the workmen to the contrary, and the ground is level, but 
it is subject to variation under particular circumstances. Thus 
the first man who has to carry the soil out of the work has al- 
most constantly an inclined plane to ascend, in order to deliver 
it on the surface, while the second man may be working on level 
ground. The work of the first would therefore be harder than 
that of the second, if both had to run equal distances. In the 
commencement of work, it frequently happens that the second 
or third stage may even be down hill, and this would make a 
still greater disparity. The first man, therefore, claims a dimi- 
nution in the length of his run, which is but equitable, and it is 
on this account frequently diminished to eighteen, fifteen, and 
twelve yards, according as the slope to be moved up Is more or 
less steep. The level runs that succeed, are each twenty yards, 
but if they slope downwards they are extended to twenty-two, 
• twenty-four, or twenty-five yards. The reason of being thus 
particular In the length of stages, is that in England the men are 
paid a certain price per cube yard for digging, as well as for each 
distinct stage of conveyance. The average price that the author 
has paid to master contractors for this work w^as three half- 
pence, (or about three cents) per cube yard per man. So that if 
two men are employed to dig and fill into the barrows, their 
work would amount to six cents for every cube so moved. Then 
each wheeler has three cents per cube yard for each stage, so 
that to dig and deliver soil on the edge of a canal or the end of 
one stage would cost four and a half cents per cube yard, and 



ON EARTH-WORK. 205 

if the soil should be carried two stages, or forty yards, it would 
cost ten and a half cents per yard. This price was customary 
for all excavation not exceeding six or eight feet in depth, but 
when it becomes deeper, the digging and filling, as well as the 
delivery to the surface, will require a proportionate augmentation 
of price. The labourers, of course, receive a less sum than above 
specified, because, out of that, the master or contractor has to 
provide all barrows, wheeling planks and implements, as welLas 
to derive his profit, and yet small as the sum may appear, the 
author found that industrious men would generally earn from 
one dollar to one and a quarter per day. 

383. The main object of dividing the shifting of earth into 
separate stages, is to avoid hindrance or delay to any one em- 
ployed; because, if the wheeler carried his loaded barrow one 
hundred or more yards, it would take him so long to go and re- 
turn, that the digger and filler would be standing still half their 
time, for want of a barrow to fill, unless a number of barrows 
and wheelers were stationed near them, and then separate tracks 
of plank would be necessary, since one barrow cannot pass an- 
other on the same plank, and such a multiplicity of tracks would 
not only be very expensive, but inconvenient, by blocking up 
the work. Notwithstanding, therefore, that the custom of work- 
men has established twenty yards as a stage, the Engineer 
should take the arrangement of the distances into his own hands, 
and make them dependent on the ease or difficulty of breaking 
down the soil at the excavation. If that yields so readily that a 
barrow may be filled before a wheeler can go and return his 
twenty yards, the stage ought to be shortened, while on the con- 
trary, if the wheelers are required to wait for the charging of 
the barrows, the stages should be lengthened, and paid for ac- 
cordlngl}^ In stage wheeling, every man should be at his post 
either with a full or empty barrow, at the moment when he is 
wanted, and thus a line of hands, whatever may be its extent, 
may be kept regularly at work without a moment^s intermission 
or loss of time. It need scarcely be noticed that at the termina- 
tion of every stage the planks are laid in a double line for a short 
distance, in order to form turning outplaces, (as in rail-roads,) in 
order that the full and empty barrows may pass each other with- 
out interference. At the lower termination of the track in the 
excavation, the planks are also laid double, in form of the letter 
Kj, so that the full barrow may be on one plank while the empty 
one is on the other, and they are wheeled, when full, alternately, 
up one and the other plank, till they reach the common single 
track. At the upper termination of the track, if a long bank 
has to be formed, several planks should be disposed in a radiat- 



206 ON EARTH-WORK. 

ing form from the single one, in order that the earth may be dis- 
tributed by carrying it first along one, and then another plank, 
which saves much after distribution and levelling. 

384. When the bank up which soil has to be moved, is ne- 
cessarily very high and steep, as for example, if it should make 
an angle with the horizon of 30° or 40°, and is perhaps forty or 
fifty feet high, an expedient, called a horse run, is resorted to. 
That is, two tracks of plank are placed upon the slope, and fixed 
there by stakes driven into the ground, and nailed or spiked to 
the planks. These tracks should be placed at a distance asunder 
that rather exceeds the depth of the excavation. Opposite the 
top of each track a post, with a large iron sheve or pulley fixed 
to it, is firmly let into the ground. The wheelbarrows used are 
of the same construction as those before described, but much 
deeper and larger, and a strong iron staple is fixed in the front of 
each for receiving the hook of a rope passing from the barrow 
in the bottom, up the slope, through the two sheves, and termi- 
nating in a liook at the second barrow upon the top of the slope, 
in such manner that the upper barrow cannot be lowered with- 
out bringing up the lower one, and vice versa. A straight hori- 
zontal horse-track is formed just behind the posts, extending 
from one to the other of them, and a strong iron ring being lash- 
ed to that portion of the rope that is constantly between the two 
posts, the traces of a horse are hooked into it, and as the animal 
is driven backwards and forwards, he will elevate one and de- 
press the other of the barrows alternately. The lower barrow 
being detached from its rope, is placed where it may be loaded 
with soil, when it is wheeled to the foot of the inclined plane, 
and the rope being hooked on to it, a signal is given to the 
driver above to start the horse, when he draws the loaded bar- 
row up the slope, a man following behind at the handles to guide 
it, and keep the barrow legs above the ground. While the load- 
ed barrow is thus ascending the empty one descends, guided in 
like manner by the man who had before accompanied it up- 
wards. His weight and that of his barrow compensating nearly 
for the man and barrow ascending on the other track. The 
ascending man has to walk in a direction nearly perpendicular to 
that of the inclined plane, so that he can exert no strength or 
muscular action to assist the barrow in its ascent; but, on the con- 
trary, a large portion of his weight is added to that of the bar- 
row; but this is compensated by the descending man, who comes 
with his face forwards, and by hanging on to the arms of his 
barrow, throws his weight upon it so as nearly to equalize the 
weight of the ascending barrow. 

385. The horse run is a slow and expensive method of raising 



ON EARTH-WORK. 207 

soil, and one that should not be resorted to except in cases of ne- 
cessity; but with all its disadvantages it is cheaper than common 
barrow work when the excavation becomes deep, because then 
the plank track must be made so very long for procuring the ne- 
cessary gradual slope, that it increases the number of sloping or 
short stages to such an extent as to be very expensive. Barrow 
and plank wheeling is always expensive, and on this account it 
should never be made use of where earth requires to be moved 
more than three or four stages. For greater distances, especially 
on nearly level ground, it will always be found most advantageous 
to cart the soil by one horse carts, built for the express purpose. 
The kind of cart most approved has only three wheels, two being 
behind and one before, the reason of which is that such carts 
stand firmly upon uneven ground, and will support themselves 
without aid from the horse; they are light and easy of draught, 
and they turn in a smaller space than any other construction of 
cart. The frame or carriage part, to which the wheels are attach- 
ed, is independent of the body, and is fastened to it by a pivot- 
bar, very little beyond the centre of gravity of the body when 
loaded, so that a very small exertion of strength is sufficient to 
tilt the body up, and cause it to discharge its load. The trace- 
chains hook on indiiferently before or behind, so that either end 
of the cart may be made to precede. In the formation of roads, 
where small protuberances of soil have to be cut off, and probably 
carried a long distance to fill up hollows for obtaining a uniform- 
ly even surface, such carts are almost indispensable. 

386. Another mode of raising soil out of deep excavations, 
without a horse run, is by what is called casting up by stages. A 
scafiblding is formed with as many boarded platforms, at five feet 
above each other, as will reach the required height. They are 
placed one beyond the other like the steps of a stair-case, and a 
man with a shovel is placed on each. The lowest man, who digs 
the soil, throws it by his shovel on to the lowest stage, and the 
man stationed there delivers it, in like manner, on to the stage 
next above him, and so on in succession, until it reaches the sur- 
face. This method is often resorted to. 

387. As earth-work proceeds, whether it be excavation or 
raised embankment, it will be necessary for the Engineer to ex- 
amine its surface every few days, especially such parts as are said 
to be finished, or are near completion, by the process of direct 
levelling, (339,) in order to see that the work is truly level, or 
has had the proper slope assigned to it, preserved. The work 
ought also to be measured as often as is expedient, and particular^ 
ly as soon as finished, lest the marks indicating the original sur- 
face should be moved or destroyed. 



208 ON EARTH-WORK. 

388. If the excavation or embankment is intended to hold or 
retain water, another process, called Puddling^ may be requisite. 
Some natural soils are of a nature capable of holding water with- 
out any artificial assistance, and clay or loam are of this charac- 
ter; others again, as sand or gravel and the debriss of stony rocks, 
absorb all the water that may be deposited above them, or they 
permit it to percolate or run through them. This likewise is the 
case with almost all artificial embankments when first made, even 
though they may have been punned in their courses and every 
pains taken in their construction; and as it is a matter of great 
importance, in the construction of navigable canals, that they 
should retain and hold all the water thrown into them, particu- 
larly where water is scarce, or their elevation is such that the 
escape of it might prove detrimental to the adjoining lands; and 
as no canal can be formed without raised embankments in some 
parts of it, so strict attention to the process of puddling, by which 
alone the escape of water can be prevented, is of the greatest 
importance. 

389. No cheap and common material is found to oppose the 
filtration and passage of water so efiectually as a soft loamy clay 
when it is well worked or kneaded into a soft paste with water, 
and is not permitted to get dry again. Even if a little fine 
gravel, or what is called by the navigators in England hoggin, 
being small sifted gravel, no stone of which is larger than a com- 
mon pea, is mixed with it, it seems to hold better, but this can 
only arise from these small stones assisting in the kneading pro- 
cess. The silt or natural deposite of tide rivers is also an excel- 
lent material, but stiff or strong and plastic clay does not answer, 
or rather it takes more time and labour to bring it to the proper 
consistency than can be afibrded, because when worked in the 
Pug-mill, to be hereafter described,for making bricks, it forms an 
excellent material for stopping water. Puddling is nothing more 
than covering the surface of ground, or of embankments, with 
this prepared clay or loam so as to enable them to hold water 
effectually, and the only difficulty is in the mode of applying it 
effectually. 

390. The ordinary method resorted to by farmers and others 
in the country for rendering their ponds water-tight, after they 
have been formed in soil that will not hold water, is to line them 
to a thickness of from six inches to a foot, with clay beaten up 
with water and wheat or rye straw by a hoe, and then to apply 
it as a plaster as soon as it has become sufficiently dry to prevent 
its slipping or sliding down. It remains exposed to the air a few 
days in order that the outer surface may become dry enough to 
maintain its form, and then the water should be \tt in upon it, so 



ON EARTH-WORK. 209 

as to fill it, and if well executed it will generally prove water- 
tight. It is, however, by no means a good or effectual process 
unless there is the certainty of the pond always remaining equally 
full, and of the water not being disturbed by cattle going into it 
to drink, or other causes. A perfect adhesion seldom takes place 
between the natural soil and this lining, consequently if it is 
disturbed, it will gradually give way and subside to the bottom 
of the reservoir, thus leaving the old surface of the ground in 
contact with the water. If the height of water is subject to 
change, a considerable portion of the top of the lining becomes 
exposed to the sun, and in drying will crack and open through 
its whole thickness, thus permitting the water to escape when 
the pond becomes full again. This may be partly prevented by 
covering the upper part of the lining with sods or turfs of grass, 
but as the grass will not grow and thrive under the water, it only 
affords protection to the upper part. 

391. The only means therefore of using a puddle lining effec- 
tually, is to inclose it within the bank in such manner that it is 
supported by earth on both sides, is kept constantly moist, is 
never exposed to the sun or external air, or indeed to disturbance 
of any kind, and then it will last and be effective for ever; and 
such is the process that should constantly be resorted to in pud- 
dling the banks of canals. This is done by forming what is 
technically called a puddle-gutter in the bank, but the manner in 
which this must be made must depend upon the nature of the 
soil to be dealt with. Thus suppose in the portion of canal re- 
presented by Fig. 103, Plate IV., that the soil bounded by the 
original surface line k /, should be clay, or any earth that is 
capable of retaining water, there will be no necessity for pud- 
dling any part of the work, except the nevvly formed bank k r q 
n, which is wholly above the surface and may require securing. 
In this case as the natural soil is good, it will only be necessary 
to form a puddle within the bank, the transverse section of 
whicli is shown by the lines u z q p, and for this purpose an ex- 
cavation must be made longitudinally in that bank like a founda- 
tion or opening for building a wall, and such an excavation is 
called a puddle-gutter. It must extend from the top of the bank 
down to the natural surface, and even penetrate at least a foot or 
eighteen inches into it, and must be wide enough for a man to 
work conveniently in it, the usual width being from thirty inches 
to three feet. All the previously contained soil having been 
thrown out, the process of puddling begins. This is performed 
by a man using a scoop-tool, like Fig. 108, and wearing a pair 
of very thick and strong boots made for the purpose, called pud- 
dling-boots. They come above the knee and should be imper- 
21 



210 ON EARTH-WORK. 

vious to water, like the high boots usually worn by fishermen. 
The ground is loosened in the bottom by the scoop, but is not 
thrown out; that done, a pretty copious supply of water is sent 
into the puddle-gutter by buckets or a temporary pump, and the 
workmen, by pressing down the scoop-tool, and walking back- 
wards and forwards in the puddle-gutter, reduces all the natural 
soil that has been disturbed into a state of very soft mud, or slush, 
as it is called. This is done for the purpose of producing an in- 
timate union and incorporation between the natural soil and the 
puddling-stuff to be afterwards added. The puddling-stufi' is 
now brought in barrows and cast into the gutter, to be treated in 
the same manner; a copious supply of water must constantly be 
given, and the more the puddling-stuff is trod and worked by 
the feet and scoop, the more perfect the puddle will be. 
Nothing is found to answer the purpose so effectually as treading 
with the feet, and the layers of puddling-stuff should never ex- 
ceed nine inches in thickness, without being trodden and worked. 
The stuff should be kept so wet that the feet sink in eight or 
nine inches at every step, and this same operation is continued 
until the puddle-gutter is filled to the top, or at any rate to a 
greater height than that at which the water in the canal or reser- 
voir will stand. Dry earth is then placed over the top of the 
puddling, to protect it from the sun and air, while the body of 
it is sure to be kept moist by the water that percolates through 
the inner part of the bank. 

392. When the necessity of puddling is ascertained before the 
work is commenced, the puddle-gutter may be formed by a less 
expensive method than that just described, because instead of ex- 
cavating it in the bank after it has been finished, it may be left 
vacant while the bank is forming, or in other words, the embank- 
ment may be formed in two separate parts, asp n q, and^ z r u; 
and to prevent the gutter falling in and getting filled with the 
materials of the bank, the puddling process may go on simulta- 
neously with it, so that the whole may be kept nearl}^ at the same 
level. 

393. It frequently happens that the whole of a reservoir, or 
portion of a canal, may be upon sand, gravel, or some soil that 
will not contain water in any part; and then, of course, partial 
puddling would be ineffectual, and the whole surface must be 
made secure. Under such circumstances it would not even be safe 
to puddle the bottom and make puddle gutters round the banks, 
because if the banks themselves were of porous or non-retentive 
materials, and they stood upon soil of the same character, the water 
would percolate through them and escape. In such a case, there- 
fore, the puddling must run under the foundations of the banks 



ON EARTH'WORK. 211 

and rise almost perpendicularly behind them, so that the work, 
instead of being excavated or formed with sloping banks in the 
first instance, must be formed with them on a nearly vertical 
shape, like Fig. Ill, Plate IV. Such was the case with the 
large reservoirs of the West Middlesex water-works, formed un- 
der the superintendence of the author about thirty years ago, for 
supplying the western part of the Metropolis of London with 
water for household purposes. They were formed wholly in 
open porous gravel, worked, in the first instance, into a shape 
like the section shown hy a b c d. A bed of puddling i e, e i, 
was then worked over the whole bottom to a depth of three feet, 
and gravel was wheeled in to form the angular slopes ei g, as 
soon as the bottom puddle had become sufficiently hard to bear 
it. Care was taken to leave the nearly vertical puddle gutters, 
a g b i and g d i c, three feet wide between the internal slopes 
as they were formed, and the natural ground behind, and this 
puddle was incorporated with that in the bottom, and carried up 
with the banks as they proceeded, so as to make the whole per- 
fectly water tight, in as unpromising a piece of ground as could 
well have been selected. Such was the scarcity of good puddling 
soil in this neighbourhood, that many thousand tons of the pud- 
dling material were transported upwards of nine miles by barges, 
on the river Thames, to form this puddle. It may appear ex- 
traordinary when it is said this was done for cheapness, particu- 
larly as good puddling materials might have been had within a 
mile of the spot. But a large quantity of soil was wanted, and 
the land must have been purchased to obtain it, and then would 
follow the expense of its excavation, and transportation by horse 
and cart, as land carriages only could have been adopted, and it 
happened that an extension of the London docks, for shipping, 
was then making, and that the material excavated was excellent 
for the purpose of puddling. The excavation at the docks was 
so extensive that room could not be found to deposit the stuff, 
and it was loaded into barges for removal. A bargain was made 
with the barge contractor to carry it the nine miles instead of 
discharging it at a shorter distance; and thus nothing being paid 
for the land or its excavation, the water carriage amounted to less 
money than the digging of it would have cost, even if it could 
have been obtained on the immediate spot where it was required. 
394. The difficulty of obtaining good material for puddling 
near the place where it is wanted, often proves a great drawback 
to the construction of navigable canals, and increases their ex- 
pense very materially. The Engineer, therefore, when he 
meets with it on a line ought to reserve it, if possible, and not 
permit it to be deposited in the banks or other places, where it 



212 ON EARTH-WORK. 

may be of no use, and from which, perhaps, it cannot be afterwards 
removed. 

395. Before the commencement of earth-work, the ground is 
very frequently covered with grass, and this is often worth pre- 
serving for the purpose of sodding banks and other work; for 
nothing preserves new work and prevents its cracking or slip- 
ping more efiectually than grass. The sods may be taken off by 
a proper tool, so as not to be more than two or three inches 
thick, and they will then bear rolling with the grass inside, and 
may thus be preserved a long time if kept from the sun in a 
moist place. When sods cannot be procured, it is often expe- 
dient to sow the ground with hay-seed. The principal matter to 
be guarded against in new embankments is not permitting large 
quantities of rain or other water to sink into them; because as 
new work is always more or less porous and absorbent, it readily 
admits water to mix with the soil, and this renders many kinds 
of earth so soft as to make it incapable of bearing the superin- 
cumbent pressure. The bottom soil is thus made to sink or 
settle more rapidly than that above it, and the upper work, by 
subsiding, is thrown out of form, and large portions of the front 
or surface work often slide or slip down the slopes, producing 
ugly and detrimental hollows, called slips, which are frequently 
difficult to repair. The best preventive of such accidents is to 
adopt a very shallow slope when working in soils that appear to 
threaten their occurrence, and to carefully provide drains or 
gutters on the top of the work, with sufficient fall to carry the 
water away rapidly, or before it has time to settle into the new 
work. 



21; 



CHAPTER VII. 



ON THE CONSTRUCTION OF ROADS. 



396. A ROAD is a certain portion of land set apart for the sole 
purpose of communication between one place and another, and 
consequently, in its formation or construction, every means should 
be adopted to make that communication as easy and commodious 
as possible. As a right line is the shortest that can be drawn 
between one point and another, so, of course, all roads should 
be made as straight as local circumstances will permit, in order 
that we may move from one^place to another, by travelling over 
the least possible portion of space; and all curves or deviations 
from a straight line will of course increase the distance. 

397. For the advantage of general conveyance, roads should 
be kept as level as possible; because, notwithstanding that 
facility is afforded to the conveyance of a load down a hill or 
slope, still as burthens have to be moved in both directions, the 
ascent of that same hill will occasion a counteracting incon- 
venience. These may appear to balance each other, and, as far 
as animal labour is concerned, they probably do so. But in a 
civilized and commercial country, time is an element that must 
always be admitted into the calculation, and it is found that the 
same space can be passed over in less time upon a level road 
than upon an uneven and hilly one, consequently the level road 
must have the preference. 

398. Roads should be as hard as possible, in order that they 
may not wear into holes or inequalities, because a smooth surface 
is indispensable to their perfection, consequently if the natural 
soil over which a road passes is not of a proper quality, it will 
become necessary to obtain and transport hard materials to place 
upon it. But the great point to be attended to in the formation 
and preservation of roads is effective drainage. If water is per- 
mitted to remain upon a road, or even in its ruts, hollows, and 
inequalities, the best materials will fail, and will be incapable of 
withstanding a heavy traffic; while very indifferent materials 
may form a tolerably good road, provided proper precautions are 



214 ON THE CONSTRUCTION OP ROADS. 

used for keeping them dry. A road should also be kept free 
from all impediments, such as mounds of earth, trees that may- 
be blown down, large stones, or deep pits; because every road 
should be kept in such a state that it may be travelled over in 
the darkest night with as much confidence as in broad day-light. 
To insure all these objects requires a certain degree of care 
and watchfulness, and frequently a considerable expenditure of 
money, and the manner in which these objects may be provided 
for, will be first considered. Roads are usually divided into three 
distinct classes, called private roads, public or parish roads, and 
turnpike roads. Public or parish roads, and turnpike or high- 
roads, are, in some countries, (of which France is an instance,) na- 
tional or government roads. 

399. Private roads are such as are constructed by private in- 
dividuals, upon their own estates or farms. In these the soil 
belongs to the proprietor, and he is alone at the expense of con- 
structing and repairing the roads. He may therefore fix gates 
and lock them up, or change their direction, or destroy and 
plough them up whenever he pleases, and the public cannot com- 
plain; nor indeed have they any right to use them, except by 
sufferance. In England, it is necessary to lock up such roads 
occasionally, and to deny passage through them except by per- 
mission, and to keep records of such stoppage; because, if a 
private road is left open to the public for sixty years, it becomes 
public property, and the proprietor cannot afterwards close it or 
even change its direction, especially if it leads to a place of pub- 
lic worship. 

400. Public, or parish roads, run through a larger district of 
country, and generally make communications between one farm 
and another, or between villages and even large towns, so that 
these roads are much more extensively used; but, inasmuch as 
they are seldom in the directions that lead directly through a 
country, they are not so much used by the general traveller as 
by those who live in their immediate neighbourhood. Such 
roads are open to the use of the public generally, without any 
toll or charge; but as funds are necessary for keeping them in 
repair, and as they require frequent inspection to see that such 
repairs are performed, they are entrusted to, and considered as 
the property of the parish in which they are situated. The 
parish appoints an officer or surveyor, whose duty It is to fre- 
quently examine the roads; to give directions to such labourers 
as may be necessary for their repair, and to provide and appro- 
priate the necessary materials. The labour, together with the 
necessary transportation of materials by carts and horses, is pro- 
vided by the inhabitants of the parish, and in order that it may 



ON THE CONSTRUCTION OF ROADS. 215 

be evenly and fairly distributed among them, an assessment Ig 
made upon every householder, according to the extent of the 
property he holds in the parish. And as this assessment is made 
by the inhabitants themselves, there is seldom any dispute as to 
its equity. According to the property of the inhabitant, or the 
extent of his use of the road, (if more than ordinary,) he has to 
furnish a certain number of labourers, horses, and carts, for a cer- 
tain number of days in each year; and they are liable to be called 
out when the surveyor has occasion for their services, and the 
entire portion of that labour being completed at any time, he is 
not liable to be again called upon in that year. The labour, 
horse hire, &c., is also estimated in money, so that if it is not con- 
venient to afford the assistance in kind when required, he may 
compound for it in money, which enables the surveyor to hire 
other assistance. These cash payments likewise fall upon such 
inhabitants as, notwithstanding their possession of property, may 
not have workmen or teams; and who, consequently, could not 
contribute at all, unless they were allowed to do so in money. 
When parishes become large and the above operation might prove 
intricate and troublesome, the labour finding system is wholly 
abolished, and a general money rate substituted in its place; so 
that the surveyor has to hire all his hands and teams, and to pur- 
chase or dig his own materials. This is, in general, found to be 
the most beneficial mode of proceeding; because the surveyor 
can, in this case, pick out and retain good hands, who become 
accustomed to their business, and work willingly and cheerfully; 
and experience fully shows that a few good hands who are accus- 
tomed to working on a road will do more good to it in a shorter 
time than a greater number of unwilling hands not acquainted 
with the business. By the former plan there must be a succes- 
sion of strange and uninstructed labourers, who may be said to 
be unwilling, because country labourers, in general, do not like 
to be put out of their regular routine of agricultural business, and 
especially to go to a work that they deem compulsory, and which, 
in many cases, is to produce a greater benefit to their neighbours 
than to themselves. Still, however, by the one or other process, 
parish roads are generally kept in a state of very fair condition. 

401. The next and most important class of roads are those 
which, in Britain, are called the high or turnpike roads. These 
are the great travelling roads which go from the Metropolis, in 
as straight lines as can be obtained, through all the principal 
towns and villages to the extremities of the country; and like- 
wise from one principal town to another. As these roads are 
for the accommodation of the general public, it would be unjust 
that the expense of their maintenance and repairs should fall 



216 ON THE CONSTRUCTION OF ROADS. 

upon the parishes through which they pass; and, accordingly, 
these roads are supported solely by tolls, taken from all passen- 
gers that use them with cattle or carriages, and they are called 
turnpike roads because they have gates called turnpike gates, and 
collecting houses placed upon them at certain distances, and the 
tolls there collected furnish funds for the preservation and repair 
of the road. As the maintenance of good turnpike roads is of the 
greatest importance to the mercantile interests of a country, and 
those of England are proverbially excellent, and are managed by 
a system, which, as far as the author's knowledge goes^ is very 
different from that pursued in the United States, and does not 
appear to be generally understood, he conceives that a short 
sketch of the system of maintaining these roads in England may 
be interesting and useful. 

402. In the first place, as these roads are of great national im- 
portance, they are all established and regulated by acts of the 
legislature. These acts impose penalties upon all persons ob- 
structing the roads, and limit the maximum amount of tolls to be 
taken from the public, by which imposition is prevented, and 
the payment of the tolls is made peremptory; for the collector 
has the right of retaining a horse or other animal in the event of 
refusal to pay the toll, until it shall be paid. As foot passengers 
are not liable to toll, of course no provisions are made respecting 
them, except that they shall not damage or impede the road in 
any way. The property and management of these roads is vest- 
ed in trustees, consisting of a number of the most wealthy, 
active, and responsible gentr}^ and farmers that live in the vici- 
nity of the road. Their number is not limited, and in the event 
of death or resignation, new trustees are named by the magis- 
trates of the county when assembled in session; and as their du- 
ties are not heavy or troublesome, and the appointment is con- 
sidered an honorary one, there are always a sufficient number of 
men to be found to undertake the office of trustee without any 
pay or remuneration. The only obligation imposed upon them 
is an oath, that they will faithfully and justly appropriate all 
funds, over which they may have control by virtue of their 
office, to the sole purposes of maintaining and improving the 
road confided to their care, and that they will perform their du- 
ties to the best of their ability. They only meet quarterly at 
some central inn upon the road for transacting business, unless 
any particular matter should occur that requires extra attendance, 
to which they are specially convened. Their attendance is not 
compulsory, though in some cases they establish a small pecu- 
niary fine among themselves for absence, the amount of which 
goes towards the expenses of refreshment at their meetings. In 



ON THE CONSTRUCTION OP ROADS. 217 

order to insure particular serveillance, the length of road confid- 
ed to any one trust is never very long, and seldom exceeds 
from ten to twenty miles in any one direct distance; but all the 
side or cross roads that branch out of the principal road, and are 
subject to tolls under the same act of parliament, are included in 
the same trust, and each trust acts under a separate and distinct 
act of its own. A turnpike road, consequently, of several hun- 
dred miles in length, would be divided into a great number of 
separate trusts, the one beginning where the other terminates j 
and as the trustees are selected from persons dispersed over the 
whole extent of the trust road, the certainty of having the whole 
length under the inspection of interested persons is thus secured, 
without imposing upon them the trouble of going far from their 
own homes. Each trust elects a clerk and a treasurer. The 
clerk is generally a respectable attorney residing in the principal 
town upon the trust road, and he is the secretary and executive 
of the trustees, to see all the orders they may issue duly carried 
into effect, and is in fact the representative of the trustees in the 
interval of their sessions, but has no power to act otherwise than 
under the directions of the board, unless such power is specially 
conferred upon him by them for particular purposes. The act 
of parliament constituting the trust, usually confers the power of 
suing and being sued at law, in the name of the trust, upon the 
clerk for the time being. For the discharge of these duties he 
receives either a competent annual salary, or a small salary, and 
is allowed to charge for his time and professional assistance in 
addition. The board likewise appoint a surveyor who is ac- 
quainted with the nature of work and road-making, and whose 
duty it is to spend his whole time upon the road; to engage, hire 
and pay workmen; to order all repairs that are necessary for the 
preservation, maintenance, and repairs of the road, with its 
ditches, water-courses, under-ground drains, and fences, and to 
take account of all materials that are delivered. Of these par- 
ticulars he makes a weekly return, accompanied by his vouchers 
for wages, and small payments to the clerk, who files the same 
for the examination of the trustees at their quarterly meetings. 
As the surveyor may have gangs of workmen employed at the 
same time in different parts of the trust, and is responsible for 
the whole line of road under his charge, being at all times in 
good order, he is not allowed to follow any other business, but 
is expected to visit every part of the road as often as possible; 
and as his whole time is thus occupied, he receives a competent 
annual salary, and in many cases has a horse maintained for him, 
and he is required to give security for the due and faithful dis- 
charge of his office. In some cases where there are manv branch 
2S 



218 ON THE CONSTRUCTION OF ROADS. 

roads that are much frequented, and which consequently render 
the distance to be inspected considerable, one trust is obliged to 
have two surveyors. 

403. All bargains for the supply of large quantities of clean 
and screened gravel, broken stones, and other materials, bricks, 
lime, or timber, are made by written contract at the quarterly 
meetings of the trustees by themselves, and at these times, orders 
are given upon the treasurer for the payment of such things as 
have been satisfactorily delivered in the preceding three months. 
The wants of the trustees are notified to the public by printed 
notices, and parties willing to supply them agreeably to stated 
particulars, are required to deliver sealed tenders of the offers 
they wish to make for such supplies, stating the times of pro- 
posed delivery, quality, prices, including hauling or delivery, 
and other particulars to the clerk, some days before a quarterly 
meeting, when the parties attend. These offers are opened, 
written contracts made, and the supplying parties enter into 
bonds for the due fulfilment of their contracts. The surveyor, 
therefore, has nothing more to do with these bargains than to 
see that the materials are delivered according to the terms of the 
contract, and to report accordingly to the clerk. 

The funds required for these arrangements are raised by tolls 
charged upon all horses, carriages, and droves of sheep, oxen, 
&c., that use the road. These tolls are limited in their extent, 
though not always fixed by the acts of parliament that raise the 
trust; because if the trustees find they can keep the road in good 
order with a less sum than the maximum tolls will produce, they 
have the option of lowering the sum, though they have no power 
of augmenting it without a new act of parliament, which cannot 
be obtained except on proof that the maximum toll is insufficient 
to insure comfort and safety to the public. In this way the 
trustees can at all times make their available income accordant 
with their necessary expenditure, and they can have no interest 
in making it larger, because the money raised can in no case be 
appropriated to any other purpose than the maintenance and re- 
pairs of the road in their particular charge. 

These tolls are collected at gates which stretch across the road, 
and have a small house for the collector adjoining them, as in 
this country. In roads of much traffic, these gates, for the sake 
of expedition, are never closed during the day, and the collector 
is constantly at his post, but they are shut and locked at night, 
though the collector is bound to rise and open them at all hours 
to any one desirous of passing: and he can shut the gate and re- 
fuse passage to any one who objects to paying the toll, which, 
to prevent imposition, is required by law to be painted and set 



ON THE CONSTRUCTION OF KOADS. 219 

forth in letters at least one inch high, on a board at the side of 
the gate. In England these tolls are only payable once in a day 
of twenty-four hours, except in a few instances of bridges; so 
that having once paid the toll a passenger can go backwards and 
forwards as many times as he pleases between twelve o'clock on 
one night and the same hour on the following one. To prevent 
a repetition of the demand, the collector is bound to give a print- 
ed pass ticket, with the name of the gate and a number, letter of 
the alphabet, or some private mark upon it, to a person on first 
paying the toll, and the reproduction of this ticket exempts him 
from further demand that day. The letter or private mark is 
changed every day, so that the ticket of one day will not pass for 
another. 

404. The trusts upon all roads, and even upon the same road, 
are perfectly distinct and separate from each other, and they have 
no interference; consequently each trust is compelled to raise its 
own funds, and it does this by having its own toll-gates. Every 
trust must, therefore, have at least one toll-gate on each of its 
principal and branch roads; or if the trustees do not think proper 
to collect the whole sum they are authorized to take, at one spot, 
they may divide that sum, and receive one part of it at one part 
of the road and the remainder at another. This accounts for the 
very large number of toll-gates met with in England, a circum- 
stance that always strikes travellers from strange countries with 
surprise. Still the principle is good, for if the number of gates 
is large, the sum taken at each of them is small in comparison to 
what it must be to raise a similar sum of money with fewer col- 
lectors. No person can travel one of these roads for more than 
ten or twelve miles, in the populous parts of England, without 
being called upon to pay a toll for the road he is using, and thus 
the burthen of keeping those roads in repair becomes very much 
divided among the whole travelling community, and the sum 
demanded from each is so small that it is not considered a bur- 
then. On the same principle the smallest tolls are collected at 
the first gates, leading out of large towns and cities, because the 
greater number of passengers using them, compensates for the 
smallness of the sum paid. By increasing the number of gates, 
the number of payers is increased, and although each contributes 
but a small sum, yet the aggregate collection produces so large an 
amount, that with the system of surveillance above described, the 
roads of England can be kept in better condition than those of 
most other countries. 

405. In the United States, as far as the author's experience in 
travelling has gone, an opposite system appears to be resorted to 
— that of using few gates — placing them near populous towns and 



220 ON THE CONSTRUCTION OF ROADS. 

cities— making the toll high, and extending over a great length 
of road. If this is generally the case, its operation must be, to lay 
a heavy tax upon the inhabitants of towns, while those who live 
at a distance from them, enjoy the free use of the road without 
paying any thing for it^ unless when they are called into town; 
and thus the distribution of expense does not seem so just and 
general. It may be urged against the English system, that the 
frequency of gates occasions great delay and trouble; but, practi- 
cally, this does not turn out to be the case, it being an ascertain- 
ed fact that there is more road travelling, and that it is performed 
with greater punctuality, comfort, and expedition than in any 
other country. The post-office vehicles, called mail coaches, 
which carry all letters, are, by law, exempt from all tolls, and as 
a difference of five minutes in the time of their arrival at any 
particular turnpike is hardly ever known, the gates are thrown 
open for them, and they pass without stoppage. The same 
may be said of all the stage coaches, which being regular and pe- 
riodical in their passage, they only settle accounts at stated pe- 
riods. This is also the case with regular inhabitants of the road, 
who use it daily. The only inconvenience, therefore, must fall 
upon casual passengers, and the collectors are so expert in giving 
change and despatching business, that this is never complained 
of; but should a little delay occur, it is amply made up for by 
the goodness of the road allowing a degree of expedition which 
would otherwise be impossible. 

406. It must be confessed that these arrangements, good as 
they are, will necessarily be attended with a very heavy expense, 
and such a one as could not be borne unless the road had con- 
siderable traffic upon it. But a good road increases traffic, by 
offering increased facilities of travelling, and an increase of tra- 
vellers produces a proportionate increase of income. Moreover, 
when once a road is got into good order, it is easily maintained 
in that order without much expense, by constantly watching it 
and mending it from day to day, which can only be done by 
having a person constantly inspecting it, with workmen and 
materials at his command, which this expenditure provides for. 
Heavy expenses only occur in roads that, by long neglect, wear 
into deep holes and inequalities, and require a strong force of 
men, horses, carts, materials, and work to repair them. Such 
neglects, are, however, never suffered to occur in English turn- 
pike roads, it having been fully ascertained that two or three 
men constantly working on a road, will do more to keep it in re- 
pair, than a gang of thirty or forty turned in all at once every 
six months, or perhaps only once in a year, which was the old 
or former practice of repairing roads. 



ON THE CONSTRUCTION OF ROADS. 221 

407. The heaviest expense incident to the English system of 
turnpike roads, is the maintenance of the toll-collectors, who 
must be stationed at the many gates, and the apparent liability 
that may exist of the trustees being defrauded out of a great part 
of their revenue by their dishonesty, if they do not account for 
all the money they may receive, or from their being careless and 
wanting in vigilance in making their collections. This is met 
and obviated by the trustees never keeping the collection of the 
tolls in their own hands, but by farming or letting them out by 
auction for stated periods, to such collectors as will make the 
highest bidding; such periods being never shorter than one, or 
longer than three years. By this arrangement the trustees are 
relieved from, all vigilance or anxiety as to the collection of the 
tolls, and it has the advantage of assuring them of the certainty 
of receiving an income free from fluctuation during the term of 
the contract, because the lessees are compelled to give ample 
security for the punctual quarterly payment of the sum they 
agree for; so that if the tolls amount to less than the sum con- 
tracted for, the loss falls upon the collector, while on the con- 
trary, all he makes above the sum paid, is his profit. There are 
many men in England who make a regular business of farming 
turnpike gates, and although they have to engage and watch over 
their deputy collectors, they generally realize money. It is 
evident under such circumstances that the trustees must be con- 
siderable losers, but their losses are by no means so great as 
they would be, if they attempted to keep the collection in their 
own hands; besides which, this plan has the advantage of making 
them acquainted with the exact sum they will receive, and it 
therefore enables them to put an exact limit to the extent of the 
contracts they can make, for labour, gravel, repairs or improve- 
ments, as well as to the salaries of their clerk, surveyor, or 
such ofi&cers as they are compelled to employ. 

408. As an instance of the vast source of income derived from 
some of the principal turnpike roads of England, near large 
cities, the great Western or Bath road out of London, may be 
adduced; for this, it is believed, is more travelled upon than any 
other road in the world. The first eight and a quarter miles of 
this road, between Piccadilly, which is the western extent of 
London, to Smallberry green near Hounslow, is divided into two 
trusts, called the Kensington and Hammersmith trusts. The 
Kensington trust has two turnpike gates upon it, at one of which 
three cents, and the other six cents are demanded for the passage 
of a coach drawn by two horses, and a single horseman pays two 
cents and three cents for his toll, and small as these sums may 
appear, one of these trusts alone, the Hammersmith, in which 



222 ON THE CONSTRUCTION OF ROADS. 

the tolls are rather smaller, used to be let for the enormous an- 
nual sum of ^10,000, or about ^50,000, all of which money- 
was annually expended in the purchase of gravel and other stones, 
bricks, mortar, and labour for spreading and laying the same upon 
and keeping in repair the drains, footpaths, and surface of less 
than four miles of the principal road, and. about ten miles of 
branch or side roads that were but little used; and in payment of 
the salaries of the clerk and surveyor. 

409. Road trustees are, in some cases, allowed to retain a 
certain limited fund of reserve out at interest on g;overnment 
security, to provide for alterations, amendments, and improve- 
ments, where they are likely to occur. And in the event of re- 
quiring a sum of money suddenly for such purposes, the tolls are 
frequently mortgaged, and are considered a full and efficient se- 
curity for such loans. 

410. In France, since the revolution, the great public roads 
belong to the government, and are placed under the charge of 
the Corps des Ingenieurs des Fonts et Chaussees, and the ex- 
pense being provided for by a general tax upon the people, the 
roads are open, or without toll-gates. 

411. The earliest law that appears to have been enacted re- 
specting roads in England, was in the year 1285, when the lords 
of the soil were enjoined to enlarge those ways where brush- 
wood or ditches were found, in order to prevent robberies. The 
next law was made by Edward III. in 1346, for laying a toll 
upon several roads leading out of London, and recited to have 
become nearly impassable. Little further relating to this subject 
occurs till the reign of Henry VIII., when the parishes were first 
entrusted with the care of the roads, and surveyors were ordered 
to be annually elected to take care of them. From this period 
the use of carriages and the transport of goods increased so rapid- 
ly, that parish aid was found insufiicient to keep the great fre- 
quented roads in repair, and this led to the introduction of toll- 
gates or turnpikes, in order that those who used the roads should 
contribute to their repair. 

412. The utility and importance of possessing good roads is 
acknowledged on all hands, and the best modes of constructing 
them is, consequently, an object worthy the attention of the En- 
gineers of all countries, and much has been done for their im- 
provement of late years. Still, however, it cannot be said that 
the improvement has been progressive, for the probability is that 
the roads of antiquity were much superior in durability, though 
perhaps not in surface, to any we now possess: that the middle 
ages wholly neglected their construction; and that our boasted 



ON THE CONSTRUCTION OF ROADS. 223 

modern improvements are little more than faint and humble at- 
tempts to attain the perfection that formerly existed. 

413. Of all people, the Romans took the greatest pains in 
forming roads; and the labour and expense they were at in ren- 
dering them spacious, firm, straight and smooth, are incredible. 
They usually strengthened the ground by ramming it, and lay- 
ing it with flints, pebbles, and sand; and sometimes with a lining 
of masonary, bricks, and rubbish, bound together with mortar. 
In some places this expensive preparation has been found to have 
been carried to the great depth of ten or twelve feet under the 
surface of the ground, making a mass as hard and compact as 
marble; and which, after having resisted the effects of time for 
upwards of 1600 57^ears, was found scarcely penetrable by the 
mattock or hammer, notwithstanding that the flints which com- 
posed it were not larger than eggs. The most noble of these 
Roman works was tlie Appian way, extending from Rome 
through Capua to Brundusium, a distance of nearly 350 miles. 
It was commenced about the year 440 of the city, by Appius 
Claudius, surnamed Coccus, and was so wide that several wagons 
could go abreast upon it, but the central part only was paved 
with very hard stone, brought from a great distance; and it is de- 
scribed, by modern travellers, as being yet in a good state of pre- 
servation, and in places, for miles together, as perfect as when 
first constructed, particularly in the paved part, which is twelve 
feet wide. 

414. The roads of the Romans were for the most part made 
for military purposes, and they were probably the first persons 
who made any regular roads in Great Britain. Such roads were 
constructed not so much with the object of improving the coun- 
try, as for facilitating the subjection of the inhabitants, and to 
secure a communication at all times between their armies oc- 
cupying different quarters of the island. They therefore stretch- 
ed across the country from one place to another in very consider- 
able lengths, constantly in straight lines from one station to 
another, and as they were all paved and placed upon the most 
elevated parts of the country for watching the movements of the 
enemy, they afforded a hard, durable, safe, and expeditious 
means of conveyance, vastly superior to the winding, soft, and 
swampy paths that had been previously formed by the earlier 
inhabitants. Many of these roads are still preserved in England, 
but as they have all been widened and modernized, no traces 
of their ancient formation exist, except their straight lined direc- 
tion, and the occasional remains of Roman camps and stations, 
near which coins and other relics are sometimes dug up, and 
they are still distinguished by their ancient names of streets, 



224 ON THE CONSTRUCTION OP ROADS. 

such as Watling street, Ikenild street, Erminage street, to 
which, however, the Foss-way, which had a deep ditch on each 
side of it, is an exception. 

415. The ancient roads were in general narrow, because wheel 
carriages, for the conveyance of goods, appear to be a compara- 
tively modern improvement, and it is not very accurately re- 
corded when, or by whom, they were first introduced. The 
war chariots of the ancients, it appears, were devoted exclu- 
sively to the purposes of war, although it might naturally have 
been expected that their use would have suggested the advantage 
of using vehicles of a difierent form for travelling and general 
transportation. Still travelling was always performed on horse- 
back, and the transportation of goods conducted in the same way 
upon the pack saddle, either on mules or horses, and hence the 
necessity of wide, fine, and level roads did not exist. 

416. As civilization reached a higher degree of perfection, 
and commerce became more extended, the occurrence of articles 
of trade or comfort in the interior districts of the country, would 
enforce the adoption of some mode of communication suitable to 
the advanced state of arts and manufactures, and the mere use of 
a wheelbarrow would carry conviction to any one that a much 
heavier quantity of produce could be conveyed, when a part of 
it was borne upon a wheel resting on the ground, than if the 
weight of the whole burthen, as well as its motion, rested upon 
the arms of a man, or the back of an animal. This would lead, 
by an easy gradation, to the formation of wheel-carriages, but as 
they are nearly useless except when moving along smooth sur- 
faces, so the introduction of such carriages would naturally lead 
to an improvement in roads, and accordingly their improvement 
and perfection generally keeps pace with the civilization and 
commerce of every country, and justifies the observation of the 
Abbe Raynal, who says: "Let us travel over all countries of the 
earth, and whenever we shall find no facility of trading from a 
city to a town, or from a village to a hamlet, we may pronounce 
the people to be barbarians; and we shall only be deceived re- 
specting the degree of barbarism.'^ 

417. As to the construction of roads, it may be said to be the 
simplest operation of the Engineer, embracing very few princi- 
ples beyond those that have been discussed in the present and 
preceding chapters, with the exception only of the preparation 
and formation of the top surface, which we shall now proceed 
to discuss. The settlement of towns, manufactories, mines, or 
other establishments that engage the attention of mankind, give 
rise to the necessity of forming roads. And the first principles 
that should govern their formation, are proximity and facility of 



ON THE CONSTRUCTION OF ROADS. 225 

passage. The first is attained by making the road of communi- 
cation as nearly right lined as possible whenever the country it 
has to pass over is so level as to admit of it; but the right lined 
direction should not be persevered in, when it is hilly and un- 
even, since a more circuitous route over a level tract of country 
is better than the shorter one that is hilly, whenever the eleva- 
tions and depressions of the soil are so extensive as to become 
inconvenient to the passenger. The operation of levelling, as 
before described, and thereby selecting a good and favourable 
line, is therefore of the greatest utility and importance in select- 
ing a good line of road. 

418. Another and most important subject to be attended to 
in the selection of a line of road, is its drainage. Many old 
roads will be found sunk beneath the general surface of the ad- 
jacent land, notwithstanding this is the worst principle of con- 
struction, and one which no pains should be spared to avoid. As 
a general rule, every road should be kept above the soil over 
which it passes if possible; and, whenever this cannot be effected, 
its surface should be enough of a hill to cause water to run down 
it; or, if level, it should have side ditches or water-courses, to 
carry off rains as speedily as possible. Common observation 
will convince any one that a road formed of almost any ordinary 
soil, without gravel or any thing to cover and protect it, will be 
good, provided it is so elevated and drained, that rain water will 
not remain upon it; while, on the contrary, a sunk road, or one 
formed like a wide ditch or shallow canal will be soft and bad, 
and will wear into holes or ruts, even if formed of the very best 
materials, and the greatest pains should be taken for its preserva- 
tion. For the same reason, a good road is scarcely ever met 
with in a thick wood, merely because the foliage shuts off the 
sun's rays, and by excluding them, and a free circulation of air, 
prevents that evaporation that would otherwise take place. Per- 
fect drainage must therefore be considered as the great and lead- 
ing requisite to the existence and maintenance of a good road, 
and this ought therefore to be the great object of attention to the 
Engineer in the setting out new roads, and the amendment of 
those that already exist. It may frequently be difficult of attain- 
ment, especially in level countries; but we will endeavour to 
give such directions as seem most likely to assist in attaining this 
most essential object. 

419. No road should be formed in a hollow or concave form, 
or even be quite flat upon the surface of its transverse section, 
but, on the contrary, should be convex or protuberant along its 
central line. If the centre of a road of twenty feet wide, is 
made six inches higher than its two sides, this will keep the 

29 



226 ON THE CONSTRUCTION OF ROADS. 

middle dry, by throwing the water to the two sides. This rising 
or convexity in the centre, is called the crown of the road, and 
as six inches is the twentieth part of ten feet, or the half width 
of the road, the crown would be said to rise one in twenty, and 
a proportionate elevation should be given to the transverse sec- 
tion of every road, whether it is narrow or wide. Such a con- 
vexity will occasion no danger to carriages running upon it, or 
any inconvenience. If such a road is above the level of the 
adjacent land, the water may be discharged from its two sides 
without inconvenience, or it may be conveyed into ditches sunk 
on the sides of the road and running parallel to it. In level 
countries, difficulties may arise in getting the water discharged 
out of these ditches, and they may require to be made very deep 
in the progress of their fall; still, it seldom happens, but that a 
vent or discharge of some kind may be discovered in the pro- 
gress of a few hundred yards; and, should that prove impossible, 
ponds or reservoirs may be sunk in the lowest pieces of land that 
can be found, in which the water may sink into the land, or be dis- 
sipated in evaporation. Avery small fall or descent will be suffi- 
cient for road ditches. They should begin at the surface, or have 
scarcely any perceptible depth at the upper part of the road, and 
become gradually deeper and wider as they descend; and all the 
soil dug from such ditches should be thrown on to the road to 
elevate it, instead of being thrown on the outside of it, as fre- 
quently practised. 

420. Whenever it may be necessary to sink deep ditches by 
the side of a road, they ought always to be separated from it by 
a foot-path or causeway, raised from nine to twelve inches at 
least above the road, to prevent accidents to cattle or carriages 
that might fall into them: the water in this case being convey- 
ed from the road by drains passing through such causeway: and, 
whenever for the purpose of drainage, it may be necessary to 
convey water from one side of a road to the other, it should 
always be carried by a drain or brick culvert running under the 
road, and in no case be allowed to flow freely over its surface. 

421. A perfectly level road is by no means desirable, on ac- 
count of its property of retaining water; and, as a very slight 
slope or inclination in the longitudinal direction will be sufficient 
to produce a discharge of water to the lowest part, while it will 
hardly be perceptible in its effect upon the draught of carriages, 
so it ought always to be obtained. By a judicious selection of 
line, and setting out of a road, sufficient slope may generally be 
found on the natural ground; but if that is impossible, it must be 
produced in the earth-work, that is to say, in the slight cutting or 
excavation that is always necessary for rendering the surface of 



ON THE CONSTRUCTION OF ROADS. 227 

the ground smooth and uniform, and fit for the hard materials 
that have to be laid upon it; and by distributing the soil that should 
be excavated from one or both sides, for draining ditches. In- 
stead of throwing the soil thus obtained upon that part of the 
road nearest to where it is produced, it may often have to be 
conveyed a considerable distance; and, whenever that proves 
necessary, carting the soil in common or three wheel carts, will 
be found more expeditious and cheap, than moving it by barrows, 
notwithstanding that barrows are preferable for short distances. 
The least slope that a road called level should have, is a yard 
perpendicular in a mile of length; but, as so slight a slope as this 
will barely affect the water, two, three, or even four yards in a 
mile, will be better, and will produce a sensible run or discharge 
of the water. A greater slope should be avoided if possible; 
because, when the slope is rapid, the water of hard rains runs with 
such velocity and force, as to wash away part of the materials 
that compose the roads or side-banks. 

422. The chief business of the excavator in cutting and pre- 
paring the surface of a country for a road, consists in what has 
been before explained in reference to Fig. 80, Plate III. (337.) 
That is to say, cutting down protuberances or projections, and 
filling up hollows, cavities, or valleys with the soil, and the only 
calculation is, that of obtaining the cubical contents in both cases, 
whether of superabundance or deficiency, to ascertain the depth 
of cutting necessary for exactly filling up the cavities without 
surplus. 

423. In forming a road upon an undulating country like that 
in the figure, the new surface should not, however, be converted 
into a right line, even though it may be one of such inclination 
as will afford longitudinal drainage, because experience shows 
that long runs of water upon roads are detrimental to them, and 
that the water should be carried off the road at as short intervals 
as possible; and such means of drainage will be obtained by pre- 
serving the former undulations of the country to such extent 
onl}^ as w^ill allow" sufficient run or discharge for the water. 
When the longitudinal slope is sufficiently great, no side ditches 
will be necessary, but the proper curvature that should be given 
to the crown will form sufficient channels, and these are called 
water-tables when they do not sink beneath the general surface, 
like ditches or gutters. Fig. 112, Plate IV., shows a profile 
or transverse section of the form the ground should be worked 
into for forming a road in level places. Suppose h h to be the 
original level surface of the land, then it must be excavated ^iff, 
to produce the necessary rounding of the road, and the soil dug 
out of these lines is thrown to the centre i, in order to raise up 



228 ON THE CONSTRUCTION OF ROADS. 

the crown. Should such a road have longitudinal slope, the an- 
gular spaces under f and f, will form the water tables. But 
should the road be level, then ditches / /deeper than the water 
table will be necessary, and the embankments k k raised by the 
soil from the ditches will form foot-paths, or causeways, and 
will sufficiently separate the road from the ditch to prevent dan- 
ger. Whether a raised footpath is formed or not, drains, throats 
or culverts, as marked under k, will be necessary for carrying off 
the water, which, as before observed, should never be allowed to 
run a long distance upon the water tables. And if it should be 
inconvenient to have a receivino; ditch on each side of the road, 
then a mere gutter may be formed at f- — and a culvert or un- 
derground drain should proceed from it, under the road itself, 
and opening into the ditch as marked at ra m. These transverse 
underground drains should be repeated at regular intervals, re- 
specting which no precise directions can be given, because their 
number and position must depend upon the form of the land, and 
the facilities that exist for getting rid of the water. Whenever 
transverse drains are introduced under a slope or hill, they should 
not be at right angles to the direction of the road, but inclined to 
it, or sloping downwards; for, although their length will be in- 
creased by so placing them, yet a much greater fall or inclination 
can be given to them, and they are therefore less liable to become 
choked or stopped up by sand and soil that will subside in them. 
They should be built of bricks, stone, or other materials not 
liable to decay, and as the opening of the road for their repairs 
may be attended with inconvenience, it is better to give them 
much larger dimensions than may be necessary for the mere 
passage of the water, so large indeed that a boy may creep into 
them with a hoe or scraper for removing any obstructions that 
occur. 

424. When a road has to be formed on the side of a hill, the 
most economical disposition will be to form about one half of it 
upon solid ground by excavation, and the remaining portion by 
■ embankment, unless the hill should be so steep as to prevent this 
mode of construction, or render it dangerous on account of the 
embankment sliding down, or giving way, when the more expen- 
sive process of forming the whole road by excavation must be 
resorted to. In general, however, the road platform may be formed 
by the former process, in the manner shown in Fig. 113, Plate 
IT^., wh^e 71 p n represents a profile of a side of a hill, on which 
the road shown in section hjop q, has to be formed. In such 
case the triangular portion of soil nop, will have to be excavated 
and removed further down the hill, placing it in the form of 
2J q 71. About one half of the road o ji, will then be on solid 



ON THE CONSTRUCTION OF ROADS. 229 

ground, and the other half, 7^ q^ upon embankment. The embank- 
ed half should be left higher when first formed than the other, 
because it will inevitably subside to a considerable extent; and, 
should any apprehension exist that the whole embankment may 
slide down, it may be prevented by cutting the hill below the 
proposed road into the form of stairs or steps, as shown in the 
figure, before beginning to form the embankment. At all events, 
whether this is done or not, the natural soil, and any grass or 
herbage upon it, should be taken off before the embankment is 
began, for such vegetable matter will take considerable time for 
its decay, and until it is gone, it forms a kind of drain or open 
joint, into which the water from above will insinuate itself, and 
prevent a due incorporation of the old and new soil; and this it 
is, in general, that occasions slijDS in new work, the occurrence of 
which should always be guarded against. When the work has 
settled, and come to its proper solidity and bearing, they rarely 
occur. 

425. In forming the kind of road just described, a banquette, 
or raised mound of earth, should always be formed at the top of 
the descending slope, as at q^ or else a strong line of wooden posts 
and rails should be fixed there, as a safeguard against passengers 
and cattle falling over. The latter, if made sufficiently strong, 
is preferable, because it admits of better drainage, and keeps the 
road-way more open and exposed to the sun and air. If a ban- 
quette is used, it should be pierced with drains at every fifteen or 
twenty yards, to carry ofi" water. In the draining of such a road 
a small ditch at o, with under-ground drains, r r, at regular inter- 
vals, is to be preferred; and, if it is adopted, the road-way may 
rise in the middle, or have a regular crown, like other roads, and 
will discharge its water on both sides as usual. A road formed 
in the side of a hill not only receives the rains that fall upon it, 
but is subject to the greater inconvenience of receiving all the 
water that may fall on the hill above it, as well as the soil that may 
wash down; and if this hilly ground is of great extent, the ditch 
and drains become almost indispensable, for the torrents of water 
thrown upon it would, unless collected in this manner, soon wash 
away or destroy the surface. If there should not happen to be 
any great surface of high land above the road, then the ditch may 
be dispensed with, but the road must have no crovvn or convexity, 
because that would produce a cavity that would hold water, be- 
tween such crown and the steep bank ?z o. The transverse sec- 
tion of the road must be a sloping right line, falling from to q, 
in a sufficient degree to let all the water that may fall run over 
the road to discharge itself from the lowest side. 

426. As to the width of roads, no rule has ever been adopted, 



230 ON THE CONSTRUCTION OF ROADS. 

since they should be made suitable to the kind of traffic expected 
upon them. As a cart or carriage can pass upon a track eight 
feet wide, and three feet more allows a foot passenger, or even a 
horseman to pass, many roads or lanes are found that do not ex- 
ceed eleven or twelve feet in width; but this is a very bad plan, 
and one that should constantly be avoided, unless in deep cut- 
ting, tunnels, or other positions, in which, from local circum- 
stances, such confined width is rendered necessary. It precludes 
the possibility of good drainage or repair, and when two carriages 
meet in opposite directions, is productive of serious inconve- 
niences, even if occasional wider passing places may have beefi 
provided. Such narrow roads are only made with a view to 
economy, but it is economy of a false kind; for, if the wheels of 
heavily laden carriages are constrained, by the narrow limits of 
the road, to move constantly in the same track, they cannot fail 
to wear it out, and fill it with deep ruts and inequalities in a short 
time; and the ruts and holes, by holding water, soften the adja- 
cent parts, and frequently render the whole impassable; while, on 
the contrary, if width had been allowed, when one track becomes 
bad, another is adopted. The vehicles, instead of continuing in 
one straight forward course, change from one track to another, 
thus traversing the ruts and inequalities obliquely, which has the 
effect of tending to flatten or fill them up; and thus a road that is 
wide, and has considerable traffic upon it, in some measure, re- 
pairs itself, of which there is abundant evidence in many coun- 
try places, where the roads are little attended to. No road should, 
therefore, ever be made less than twenty-four feet in width for 
any purpose, and in those that are much frequented, from thirty 
to sixty feet will not be found too much. 

427. We wdll conclude this account of the setting out and 
formation of roads, by a few observations that apply generally to 
them in all positions and situations. Notwithstanding a perfect- 
ly straight line forms the nearest communication between one 
place and another, and can very frequently be obtained in setting 
out a road, still, if it continues for miles in succession, it is gene- 
rally admitted to be irksome to the traveller; and, as a gentle un- 
dulation or waving of the line produces very little addition to the 
length, and adds to the beauty of a road, it may be safely admit- 
ted, and will in general be approved. When the necessity oc- 
curs of a road changing its direction, it should never do so ab- 
ruptly, but in the form of a long and gentle curve, such a line 
being more safe and consistent with rapid travelling, than sudden 
turns, which ought only to be admitted where one road crosses 
another, and then sufficient space should be left at the intersec- 
tion to admit of carriages taking such curved direction; and, in 



ON THE CONSTRUCTION OF ROADS. 231 

every case a certain distance of the road in advance, should be 
open to view, to avoid the unexpected meeting of what may be 
moving in an opposite direction. Guide posts, indicating the 
place a road leads to, should also be set up at all intersections of 
roads. They are often disregarded by local inhabitants, as being 
useless to those who, living in the neighbourhood, know every 
road, but they are highly useful, and save much time and anxiety 
to strange travellers. In England the road trustees and parishes 
are bound, by law, to provide and maintain them as part of the 
road expenses; and the plan lately adopted for making them is 
good and convenient. The indices, or pointers, fixed to the top 
of the post, instead of being made of wood with the place painted 
upon it, (and which is very apt to be defaced,) is made of cast 
iron, and consists only of letters about three inches high, attach- 
ed to the surrounding frame, so that no ground or board is necessa- 
ry, but the whole is transparent with the exception of the letters, 
and these being seen against the sky, can be read after it is so 
dark that no other writing would be visible. The appearance of 
such a casting is shown at Fig. 114. The number indicates the 
number of miles to the place named, and may be used or not at 
pleasure. 

428. In all great roads, mile stones should be set up to indi- 
cate the distances to and from places; and these, of course, are 
placed at intervals of one mile asunder. Formerly the distances 
were indicated by posts of wood, painted; but these being sub- 
ject to rapid decay and obliteration, were replaced by stone posts; 
which, although durable in themselves, are not so in their in- 
scriptions. They might answer if formed of marble or any good 
stone for maintaining carving, but in many parts of England 
they have been formed of the nearest local stone, to avoid the 
expense of transportation, and the consequence is that many of 
them are illegible. Of late years, cast iron has been resorted to, 
particularly in the north-eastern roads of that country, and is 
found to answer the purpose in a more satisfactory manner than 
any material previously resorted to. They do not require great 
strength or weight of metal, and are often fixed upon the face of 
the old ponderous stone. The form adopted is so convenient 
that it may be worth copying, and is as follows: The casting 
consists of two flat sides about fifteen inches wide, and about 
three and a half high out of the ground, placed at right angles to 
each other, and united at the top by a triangular piece that slopes 
so as to make an angle with the horizon of about 60°. The 
whole is cast in one piece, having the appearance of Fig. 115, 
Plate IV., and the letters stand out, or are in relief. The large 
figure on the top is the distance from the metropolis, London, 



232 ON THE CONSTRUCTION OF ROADS. - 

and the two sides present the distance from the nearest post 
towns in the two directions of the road. Being hollow, they 
may be attached to a post of stone or wood, or the cast iron may 
be prolonged sufficiently to be set in the ground. They are 
painted white, and the letters black, so as to be seen at a dis- 
tance, and are not only exempt from obliteration, but are cheaper, 
and, it is believed, better than any previous method of marking 
the distance upon roads. 

429. In many places roads are unavoidably subject to floods, 
or freshets, so as to become occasionally covered with water. 
When this is the case, the projDer direction of such road should 
be indicated by posts placed at convenient distances along their 
sides, with figures, cut or painted upon them at every foot from 
their bases, so as not only to guide the traveller in his proper 
track, but to inform him what depth of water he has to pass 
through. 

430. Trees and live hedges are, without doubt, pleasing to the 
eye, and add much to the beauty of a road, but at the same time, 
they are highly detrimental to it, particularly if placed at the 
south or sunny side. Hedges, therefore, should be kept low by 
cutting, and trees ought not to be permitted, particularly if their 
branches are long and overhang the road. Many advocate the 
planting of a road side, on account of the pleasant shade produc- 
ed, which is desirable during the hot season; but if trees are 
sufficiently large for this purpose in the summer, they will inevi- 
tably produce more than an equivalent mischief in winter or 
wet seasons, by their retention of water, and dripping upon the 
road, as well as preventing its becoming dry when the rain has 
ceased. A good piece of road, overshadowed by trees, is a thing 
of very rare occurrence. 

431. It only remains to speak of the manner of rendering 
roads hard and durable after they have been set out and formed 
as before directed, and this can only be accomplished by cover- 
ing them with hard materials. What these materials will be 
must in general depend on the locality of the road, and its hap- 
pening to be in a completely inland country, or one that has the 
advantage of navigation. There is no doubt but that the hardest 
flint stones make the best road, and next to them the whin stone, 
Trap and Basaltic formations, but they are not procurable in all 
places, and therefore the best materials that can be obtained in 
the immediate neighbourhood must be resorted to, and in their 
selection, hardness and tenacity are the great objects to be re- 
garded. When countries are near navigable rivers or canals, it 
often proves more economical to transport hard materials from 
a distance, than to use the softer ones with which a country 



ON THE CONSTRUCTION OF ROADS. 233 

abounds. No material is more universally distributed over the 
face of the earth than what is called gravel, and accordingly that 
is generally used for making roads. . 

432. Gravel is a general term applied to all stones that have 
the form of pebbles, whatever their composition may be, there- 
fore it is not admitted as the name or character of any particular 
stone in mineralogy. The hypothesis usually held respecting 
pebbles is, that they are fragments of rock broken or separated 
from the large masses, by decay of parts, or by some great con- 
vulsion of nature, and that they have been rounded by having 
their j^oints and sharp edges worn oif by attrition in the sea, 
from whence they have been deposited, by means of which we 
have no record, in various parts of the dry land, and frequently 
at elevations far above the present reach of the sea. ' These peb- 
bles, therefore, vary much in quality, even in the same parcel of 
gravel, but they are almost universally hard, because the process 
they must have undergone to bring them to the form of pebbles 
would grind the softer materials to a state of powder, producing 
either sand or common soil; and as flint is the hardest of all com- 
mon or ordinary stones, so the pebbles of gravel are usually of 
this material. 

433. What may be designated under the general name of 
gravel, is divided into several classes, by names dependent only 
on the magnitude of the component parts. Thus large rounded 
pebbles, which are never quite round, but are flattened on their 
two opposite sides, and which are found abundantl)^ on many 
sea shores, of a magnitude varj^ing from that of a man's fist to 
his head, are called boulders, and these are picked up separately 
and reserved for the purpose of paving streets. What is gene- 
rally understood by gravel has no stones in it larger than the 
fist, but it has all gradations of smaller ones down to sand. 
The sort always used, or at any rate preferred for road making, 
is termed clean, or screened gravel, that is to say, the mixed 
gravel passed through a screen or sieve composed of very strong 
iron wires, or rather thin rods of iron placed at from half to 
three-quarters of an inch asunder. All that will not pass through 
such a screen is termed screened gravel, and that which does 
pass through is, by workmen, termed hoggin, before referred 
to (389). The first is alone used for road making, and the lat- 
ter for covering causeways, footpaths and gravel walks; it con- 
sists of a mixture of sand and small pebbles, which bind together 
and produce a hard, smooth, and compact surface. 

434. The old system of road making, or rather road covering 
and repairing, as followed in England, and which is still perse- 
vered in in many places, was, after having prepared the ground or 

30 



234 ON THE CONSTRUCTION OF ROADS. 

sole of the road ?jy giving it its proper crown or convexity, 
slope, water tables, and so on, to cart and spread as much screen- 
ed gravel, without any previous preparation, as would cover the 
whole road to a depth of from nine to twelve inches, and then to 
cover this with a thin coat of hoggin, in order to fill up the in- 
terstices, and cause the gravel to bind or become compact. This 
produced a very rough road at first, but by time and use it would 
become compact and tolerably smooth. In this way it was left 
until it needed repair, and that repair consisted in first scraping 
ofi'all soft mud, and then applying another coat of screened gra- 
vel without hoggin, so as to cover the old road to a thickness 
of two or three inches, spreading it by rakes or shovels, to 
make the surface as even as possible, and to fill up the old ruts 
and inequalities, and this was repeated every fall or autumn. 
This practice was continued until Mr. M'Adam, of Scotland, 
drew the attention of the public to its waste and impropriety, 
and introduced his improved system of road making, which he 
began about the year 1810, and which is now almost universally 
followed. He was led to the consideration of this subject by 
observing the effect that took place when a heavy carriage, such 
as a loaded stage-coach, passed over a newly formed road. The 
wheels being thin and narrow, cut or sunk into the new gravel 
to a considerable depth, so as to make the draught enormously 
heavy, and they were permitted thus to sink in, on account of 
all the gravel pebbles being hard and round, which allowed 
them to roll about and displace each other, thus completely 
counteracting any tendency they might have to bind or unite to- 
gether into a hard mass. Every vehicle that passed in succes- 
sion produced a new disturbance or displacement of the mate- 
rials, to such an extent that it might almost be compared to 
ploughing up the road; nor did the road begin to assume a good 
and hard aspect, until by the repeated passage of heavy carriages 
over the materials they were broken and partly reduced to powder. 
In the same way when a road was repaired by giving it a new 
coat of coarse gravel, without disturbing the old surface, the 
wheels constantly made their way through that new coating 
down to the old surface, displacing the new gravel, unless it was 
applied in a very thick and expensive manner, and thus the re- 
pairs never availed until the new material was partly worn out, 
as it was supposed, by becoming broken. In the formation of 
his system he was guided alone by what he saw going on in na- 
ture. If the road did not become hard and good until the stones 
were irregularly broken by the frequent passage of heavy car- 
riages over them in process of time, why impose the duty of 
breaking the stones upon the carriages, when it could be more 



ON THE CONSTRUCTION OF ROADS. 235 

speedily, effectually, and regularly done in the first instance, by 
hard labour? Again observing that when a carriage wheel, or 
even a horse's foot fell upon a large stone that was imperfectly 
bedded or fixed in its place, such stone would be moved, or per- 
haps turned over, by which a disturbance of all the smaller stones 
around it took place, and they became loosened and disturbed, he 
became satisfied that no large stones should be used. The leading 
feature in M^Adam's system of road making, therefore, is that 
no large stone, or stone of a spherical or rounded form, however 
small, should be introduced into the formation of a road, but that 
the operation of breaking them should be resorted to in the first 
instance, before they were used upon the road; thus not only re- 
ducing them to small magnitude but likewise producing sharp 
points and angular edges upon them, in order that they might 
lock into each other, and nearly, if not quite, destroy their ten- 
dency to roll about or give way to pressure; and this has been 
attended with the happiest result, for a bed of broken stone of 
much less thickness than the gravel formerly used, is found to 
consolidate sooner, and to produce a much more durable and 
compact surface than could be formerly obtained; besides which, 
the broken stones preserve the form in which they are placed 
upon the road, while in the old plan the rounded pebbles had a 
constant tendency to shift from the middle of the road, which is 
most used, towards the sides, thus requiring the occasional use 
of the hoe and rake for several weeks, to draw them to their 
former places. 

435. Another objection to the use of rough or unprepared 
gravel arises from the various dimensions of its component parts. 
The small and fine stuff has a tendency to set to the bottom, 
while the large stones work out to the surface, and occasion in- 
convenience and irregularity, with great additional wear and tear 
to wheel carriages, until they are broken down; while in the 
M^Adam plan, as all the stones are reduced to nearly the same 
size, this effect cannot take place. 

436. Mr. M^Adam also adopted a new system in the repair 
of former roads, although one of his principles was that a road 
should never be permitted to get out of repair, which may be 
effected for a long period, by care and watchfulness. The me- 
thod of obtaining this desirable end is by having single cart 
loads or small heaps of ready broken stone disposed at short dis- 
tances upon convenient places on the waste ground at the sides of 
finished roads, or wherever they would be out of the way of 
passengers, and keeping a single labourer to inspect a certain 
distance of road, who, v/ith a wheelbarrow and shovel could take 
the few stones necessary to fill up a cavity or rut as soon as it 



236 ON THE CONSTRtJCTION OF ROADS. 

appeared, from the pile nearest to it, and thus by keeping the 
whole level, none of those concussions of heavy loads occurred, 
that are more hurtful to roads than anything else. A road suffers 
little from a heavy load drawn upon it, provided the surface is 
smooth and regular; but when ruts or holes occur, the wheel 
sinks into these with all the increased momentum of the fall, and 
produces an effect that may be compared to that of a prodigious- 
ly heavy hammer falling upon the spot: and thus the hardest 
materials soon crush and are ground to dust, while no such effect 
occurs on the road while kept with a smooth and even surface. 

437. Still, however, the materials will wear out and give way 
in time, so as to require renewal, and whenever this has to be 
done, broken stone alone is to be resorted to; but instead of plac- 
ing it upon the old smooth surface, as formerly done, and where 
a very imperfect incorporation took place between the old and 
hard surface and the loose new materials, he prepares the former 
road by picking up its top surface with a short and heavy pick- 
axe to a depth of at least two inches, so as to render it quite 
rough, or like a newly formed road in appearance, and upon 
spreading the new stone to a depth of three or four inches upon 
it, a complete binding and incorporation takes place in a very 
short time. To this process he therefore applied the new name 
of lifting a road instead of repairing it, though in fact, the lifting 
only applies to the raising of the old surface to prepare it for 
proper incorporation with the new material. The road being 
repaired, has to be v/atched as before stated, for a few weeks, to 
fill up any cavities that may occur, since it is impossible, either 
in making a new road or repairing an old one, to dispose the 
materials so equably as to insure that one part shall not sink 
more than another; but when once these inequalities have been 
adjusted, and the whole surface has become uniformly hard and 
smooth, it may be left with confidence, as deep holes or ruts oc- 
cur through negligence alone. 

438. It may at first sight appear that the breaking of stones is 
a tedious and expensive process: so it is in the first instance, but 
it affords employment to old men and children who might not 
be otherwise employed, and the expense is amply repaid by the 
smaller quantity of stone required, and the little repair necessary 
to the road when once properly made. When first adopted, 
Mr. M^Adam used an iron ring as a gauge for the size of the 
stones, and no stone was considered to be broken small enough, 
unless it would pass through that ring. Now the stones are cart- 
ed in their rough state to the road side. The labourers sit upon 
the heap, and selecting a large stone as an anvil, they break the 
larger ones upon it with a long steel hammer, taking one at a 



ON THE CONSTRUCTION OF ROADS. 237 

time, and throwing them, as broken, to one side. The work is 
paid for by the bushel of broken stone^ and this being measured 
in the presence of the surveyor or his overseer, if he meets with 
any stones that the breaker cannot take between his teeth, the 
work is considered imperfectly done, and is not paid for until 
the heap has been gone over again. This is a sufficiently accu- 
rate gauge, and operates as a check upon the inattention of the 
workmen. 

439. After a new road has been formed, or an old one repair- 
ed, Mr. M^Adam recommends the use of a very heavy cast iron 
roller to be drawn by horses over the newly laid stone, to render 
it more speedily solid and compact than it otherwise would be. 
But a roller of sufficient weight to do good, is so heavy and ex- 
pensive that it is not alwa5''s resorted to. Such a roller ought 
to be about six feet long by four or five feet in diameter, and 
full an inch and a half thick of metal, to be effective. And lastly, 
he insists, (as we have already done,) in the absolute necessity 
of good and perfect drainage for every road; saying that if the 
substratum of natural soil is not kept dry and hard, we may in 
vain look for a perfect road, since the best materials will be 
pushed or driven down, and will be buried in the natural soil if 
soft, by every passing load, and in their passage downwards they 
raise and protrude a quantity of that soil, about equal to 
their own bulk, on each side, which disturbs and mixes with the 
broken stones, and renders them unfit for their office, by destroy- 
ing the foundation they should rest upon. Indeed, so essential 
it is to the preservation of a good road that it should be kept 
dry, that the mud or slush remaining on the surface of roads af- 
ter continued rain, ought never to be permitted to remain and 
dry there, but should be scraped off and put in heaps at the sides 
of the road to dry. This scraping should be performed by 
wooden hoes, about a yard long, as iron ones draw up the stones 
and produce irregularity. The road stuff, when so collected and 
dried, forms the best sand for building mortar, and is in general 
very good for lining furnaces in which great heat is required, 
and also forms excellent foot-paths. 

440. The greatest difficulty a road-maker has to contend with 
is a bad substratum or natural soil. If that is good and hard, and 
so situated that it can be drained, a good road may always be 
formed, especially if good gravel or other sufficiently hard mate- 
rial can be found to cover it. In clay countries, where gravel or 
stone of any kind is scarce, an artificial material may be formed, 
(if wood abounds,) by making the clay into balls and burning 
them until they are nearly vitrified. On the same principle, the 
slag or refuse from iron and other furnaces, makes an excellent 



238 ON THE CONSTRUCTION OF ROADS. 

material. In the neighbourhood of collieries, the stony or slaty 
part of coal is used, and in the south-west part of England many 
of the roads are formed wholly of hard or stone-chalk. In fact 
almost any thing, except sand, will make a tolerable road, if kept 
dry, properly scraped, cleansed and attended to, and the substra- 
tum is hard, dry, and absorbent. Hardness alone is not sufficient, 
for solid and compact rock is a very bad bottom, unless when 
covered by so thick a stratum of good material, as will prevent 
the surface water from sinking down to it, or its irregularities 
from being perceived. Rocky countries are generally very 
broken and hilly, and owing to the smooth surfaces presented, 
and the water being unable to penetrate into them, the materials 
will not adhere and become fixed, but are very liable to be wash- 
ed away by the floods of rain, so frequent in such places. A 
sandy substratum is also difficult to conquer, except by such a 
thickness of gravel or broken stone as will entirely prevent any 
concussion or vibration that occurs at the top from being trans- 
mitted below. Should it take place, the lower stones will sink 
gradually into the sand, which will rise and mix with the upper 
stratum, thus making room for that to descend until the whole 
may be lost or buried. The most effectual method of counter- 
acting this effect is to dig the sand out to about a foot in depth, 
and to place large and flat stones upon the bottom, so that they 
may take an extended bearing upon the sand; to fill in with large 
broken stones, or old brick rubbish, if it can be procured, and to 
finish with stones broken to the usual size. The worst bottom, 
however, that has to be contended with, is a bog-swamp or morass, 
in which the ground is soft and full of water, so as to be incapa- 
ble of supporting small stones, and from which no drainage of the 
road-way can be obtained. It frequently happens on inspecting 
a situation, even like this, that some outlet may be found for 
draining off the top water of a morass, though, perhaps, only for 
a foot or two, and yet this will at times render the surface better, 
though it will generally sink or become lower when the water is 
drawn away from it. It is, however, advisable to drain it as far 
as possible, and that done, there is no better way of forming a 
road-way than by placing fascines, (as they are called in the lan- 
guage of military engineering,) or bundles of brush-wood tied 
together, and disposed regularly by the side of each other in the 
manner of paving, and then placing a second course above these, 
laid in the cross or opposite direction; the next, or third course, 
should be parallel to, and in the same direction as the first. The 
number of layers or courses of these fascines will, of course, de- 
pend on the nature of the place, and the quantity of sinking or 
depression that will take place when they are loaded with gravel. 



ON THE CONSTRUCTION OF ROADS. 239 

Should the place be very bad, two or three courses may be laid, 
and then covered with small poles or young trees, laid across the 
intended road-way, (in the manner practised in this country in 
wet and soft places,) when other courses of fascines or faggots 
should be laid upon them; the only use of the poles being to bind 
the whole together, and prevent the possibility of one part sink- 
ing without another, thus extending the pressure over a consider- 
able quantity of surface. The platform of fascines, being thus 
formed, should be covered with large and flat stones if they can 
be procured, and a thin stratum of loam or clay, that is nearly 
impervious to water, is sometimes laid over them, after which 
the road is gravelled or covered with stone, in the usual manner. 
The weight of the road materials will generally cause the fascines 
to sink in the soft bottom until they disappear, and sometimes 
even the whole road may sink to such an extent as to become 
useless; and the only way of recovering it is to repeat the 
former process until a good and hard road is obtained. 

This is a very expensive mode of proceeding, and one which, 
of course, would never be adopted, except when local circum- 
stances render it absolutely necessary; because, in most instances, 
it would be better, and probably, cheaper to go a few miles round, 
than to cross directly over a bog or morass. It is, however, a 
common mode of construction in Holland, where a great part of 
the land has been reclaimed from the sea, and is actually under 
its level; the water being kept out merely by sea-walls and em- 
bankments, and a great part of the soil would be constantly under 
water, was it not for the constant operation of pumping, which is 
carried on without any great expense beyond the first cost of 
machinery, which consists of an immense number of wind-mills 
or pumping-engines, driven by the force of the wind alone. This 
power, it is true, is an uncertain one, but it is cheap and availa- 
ble, in almost every position, and is found to answer the purpose 
most effectually. It is often resorted to in England for grinding 
corn, with good effect, but is not yet much known in the United 
States, which are so bountifully intersected by fine rivers, afford- 
ing ample water power, that there is little need of further assist- 
ance. Still the power of wind might be rendered available in 
many places where that of water cannot be obtained, and it is 
worthy the attention of the agriculturalist and manufacturer. It 
might be supposed that the fascines and timber placed under a 
road, upon a morass, would soon decay, and destroy the road; 
but this does not occur, provided the timber sinks in, and is not 
exposed to air. Whole trees are frequently dug out of bogs 
without any appearance of decay, though no records may exist of 
the time of their disappearance. And the celebrated Peten dike, 



240 ON THE CONSTRUCTION OP ROADS. 

ill Holland, constructed centuries ago by this process, is as stable 
as ever, and its fascines and rails, when dug up, are in the most 
perfect state of preservation. 

441. Whenever roads are subject to a more than ordinary use 
and wear, it is found more convenient and economical to pave 
them, instead of covering them with loose stones. Thus the 
streets in all cities and large towns are paved, which not only 
insures better and more regular roads or tracks for carts and car- 
riages, but promotes the cleanliness and health of the place, by 
the facility that is provided for the escape of rains and other wa- 
ter, and of clearing away the dirt and filth that never fails to 
accumulate in thickly populated places. 

Paving is nothing more than selecting good and hard materials, 
as nearly equal in size as possible, and disposing them in a regu- 
lar and close manner upon the surface of a road, previously form- 
ed in the same manner as if it was intended to cover it with gravel. 
The goodness and duration of pavement depends on three cir- 
cumstances, which require particular attention, viz: the materials 
employed; the bottom or substratum on which they are placed; 
and the manner in which the work is performed; and these must 
be separately considered. 

442. The material that has been generally selected for paving 
the cities and towns of the United States; of the old part of 
Paris, and most of the provincial towns of France and Britain, 
and which was, until about twenty-five years ago, wholly em- 
ployed in London, is the large boulders or rounded pebbles before 
spoken of, as having a spheroidal or flattened spherical form, and 
a magnitude of six or eight inches diameter in one direction and 
about half as much in the other. They generally consist of 
granite whinstone, or trap rock, supposed to have been reduced 
to the rounded form by long attrition in the sea, and they are 
usually collected on the coasts. Notwithstanding the general 
adoption that has been made of these stones for paving, they 
possess no advantage beyond their hardness, and their producing 
a surface that the feet of horses do not slip or slide upon, in con- 
sequence of the numerous small projections and irregularities they 
present. In using them for the purpose of paving, they are 
placed close by the side of each other, with their longest diame- 
ter upwards, or in a vertical direction, and, if one end of the 
stone happens to be smaller or sharper than the other, that end 
is placed downwards. The disadvantages of this kind of stone, 
are, that owing to their thin rounded shape, they are incapable of 
bearing or supporting each other laterally, except in single points; 
being in some measure sharp or wedge-shaped, they cannot take 
a good or flat bed or bearing upon the sole or earth prepared 



ON THE CONSTRUCTION OF ROADS. 241 

beneath for receiving them; they are so light that they receive 
and transmit the pressure or concussion of every load that passes 
over them to the earth that supports them; and, as their joints 
can never be brought into any thing like close contact on their 
upper surface, they present what may be compared to an innu- 
merable quantity of small funnels to catch and retain the rain 
that falls on them, and very effectually prevent it from running 
off; the consequence of which, is the formation of inuch mud 
and dirt in wet weather, and of dust when it is dry; and as the 
water thus retained in the cavities has no opportunity of escaping 
except by evaporation, and principally by percolation, the sub- 
stratum is kept constantly moist, and rendered less effective than 
it otherwise would be, in resisting pressure from above. From 
the small depth of these stones, the frost of winter penetrates, 
and freezing the moist earth below, causes it to expand, and pro- 
trude the stones from their places, and when a thaw returns, the 
ground having been rendered soft, permits them to sink un- 
equally, and thus to destroy the even surface they before present- 
ed. As the stones sink, a portion of the substratum is dis- 
placed, and protruded between the joints, so as to afford ample 
materials for the formation of mud in wet weather, which is 
washed away by the rain, thus affording room for the collection 
of a fresh supply, which cannot fail in a greater or less degree 
to mix with the offal of the streets, to such an extent as occa- 
sionally to become offensive. Lastly, the unavoidable inequali- 
ties of a boulder paved road, produce a degree of wear and tear 
in all carriages of rapid movement well known to those who use 
them; and they are equally unfavourable to the shoes of horses, 
as well as being far from good for their feet; and the noise they 
produce is a universal source of complaint among those who live 
in busy cities. 

443. A really good material for paving carriage-roads should 
be hard and durable; in masses so large and heavy as to afford 
effective reaction to the concussions of loads that move upon it; 
should present a surface so smooth as to retain or hold no water, 
and offer so little resistance to wheels passing over it, that no 
sudden jolts or concussions would be produced, and would, 
therefore, admit of even rapid motion with little or no noise, and 
damage to vehicles, and yet should be sufficient!}^ rough to afford 
good foot hold to horses. The joints should be so close, as 
neither to permit much water to pass through them, or of sub- 
soil to rise up, which it will have no tendency to do while kept 
dry; and, above all, the bottom of the material should be so flat as 
to permit it to rest and bed in a solid manner upon the sole or 
ground prepared to receive it; and no material that does not pos- 
31 



242 ON THE CONSTRUCTION OP ROADS. 5 

sess some, or the whole of these qualifications, should be allow- 
ed to form the pavement of good or much frequented streets. 

444. Many expedients have been resorted to in order to ob- 
tain these advantages. At one time, large blocks, or rather 
hollow boxes of cast iron, with roughened surfaces, and, at 
another, thick plates of the same metal were tried in London, 
but were objectionable, not only on account of expense, but from 
their wearing too smooth for horses to travel upon, and pro- 
ducing a disagreeable noise. In New York, square blocks of 
timber, with the grain running vertically, were tried, and 
answered perfectly for giving foot-hold, and destroying noise; 
but they could not be expected to maintain their level surface 
long, and from the nature of the material, must be subject to 
rapid and unequal decay, therefore they have not been encour- 
aged. Nothing has yet been discovered that so completely ful- 
fils all the conditions o^ a good pavement, as square blocks of 
the hardest granite, which material is alone used in London, and 
the modern parts of Paris. Upwards of twenty years experi- 
ence of the use of this stone, in the most crowded and busy 
streets, has fully tested its value, not only as to duration, but as 
to cleanliness, comfort in travelling, freedom from dirt and noise, 
and length of time that intervenes without necessity of repair; 
so that although this material is brought by sea from Aberdeen 
in Scotland, a distance not less than six hundred miles, it proves 
cheaper in the end than any thing else that has been tried. The 
nature of the stone prevents its ever becoming smooth or polish- 
ed by use, and hence it presents as good and firm a foot-hold for 
horses after years of wear, as when it is first laid down; and 
being uniform in its texture or hardness, it wears equally. The 
closeness of the joints permits little or no water to penetrate, 
and it is never affected by frost, and never gets into partial holes. 
There is a great variety in granites, as will appear in the next 
chapter, but the kind selected for paving stones, is very hard and 
fine grained, contains very little mica, and is very similar in 
colour, texture, and hardness, to the stone brought from the 
neighbourhood of Boston, and now so extensively used for 
making jambs, story posts or pilasters, for supporting the fronts 
of modern stores in New York, Philadelphia, and some of the 
principal cities. As excellent granite for the purpose of paving 
is so abundantly found in the northern states, and is convenient 
for water conveyance, it is confidently hoped that its efficacy will 
ere long be tried in some of the principal streets, so that the 
pebble or boulder pavement that now disgraces them, may be 
gradually banished, as it lias been most effectually in London, 
into alleys, unfrequented lanes, and provincial towns. The ex- 



ON THE CONSTRUCTION OF ROADS. 243 

periment may be tried on a small scale, as it was in London in 
the first instance, by paving a single principal street, and trans- 
ferring the stones taken up to any newly formed street of less 
importance in the suburbs, to prevent their loss; and the author, 
on his own experience, can assert, that it will give satisfaction 
and spread rapidly. It was so began in London; whenever a 
piece of boulder pavement required to be taken up for repair, it 
was relaid in granite, and the old materials removed; and all new 
streets were laid with granite in the first instance, so that in the 
course of a few years, a boulder paved street could hardly be 
found, and it became necessary to export the boulders by water- 
carriage to any places that would buy them. A few years ago, 
the corporation of the city of Bristol in England, came to a re- 
solution to repave nearly the whole of that city at once with 
granite, which was undertaken by an opulent paving contractor, 
who bought the whole of the boulders, and having delivered a 
sufficient quantity of granite to the place before the streets were 
touched, the whole pavement of the city was changed in a very 
few weeks, by employing a yery strong party of able workmen. 
445. In working granite quarries, it is impossible to get all 
the pieces exactly of the same size, and they are therefore assort- 
ed at the place, those that are similar being placed together; for 
it is essential to the perfection of granite paving, that all the 
stones used in the same street should be similar in dimensions, 
(at all events as to height,) in order that they may lay evenly 
upon the smooth surface prepared for them. If this was not the 
case, the long stones would require holes to be made in the pre- 
pared surface to receive them, and the shorter ones must be block- 
ed up by pushing sand or earth beneath them., as must be done 
with unequal boulders, and this is one cause of their getting so 
soon out of level. The blocks used in the best streets of London 
are twelve inches long and eight inches wide on the top surface, 
and ten inches deep, or high, from top to bottom. The crossings, 
for foot-passengers, are of the same m.aterial, but, generally, 
rather larger on the face, and about an inch deeper, so that they may 
protrude a little above the general surface, for the sake of clean- 
liness. The smaller blocks are reserved for less important streets: 
but no stone is used, even in these places, that will not measure 
nine inches from top to bottom. And in addition to their being 
measured, they are constantly weighed in scales, and such as are 
too light, are rejected as being of a less dense and hard quality, 
if their size is equal to the others. 

446. The method of laying pavement is very simple. The 
road must be prepared for receiving it just as another road would 
be treated for receiving gravel, except that greater care is neces- 



244 ON THE CONSTRUCTION OF ROADS. 

sary in having it all of one uniform hardness; because, if the pave- 
ment sinks partially, it is more difficult and expensive to repair 
the failure than in a gravelled road. The surface is levelled, 
rounded into a crown, and the side gutters formed in earth ex- 
actly as it is meant to appear when paved; because, if the stones 
are all of equal height, the paved surface, when finished, must be 
parallel to the prepared surface of earth, which is called the sole. 
To insure an equal hardness in the sole, it is always advisable to 
go over it with a beetle or paving-rammer, before the stones are 
placed; this will show if any soft places exist, and if they are 
found they must be filled in with gravel or hoggin, and be ram- 
med until they become hard and level like the rest. Previously 
to forming and finishing the sole, a row of curb-stones must be 
let into it, on each side, for the purpose of forming a border or 
finish to the paving, for keeping the exterior rows of stones in 
their places, and to make a boundary to the paved foot-paths 
that are usually placed on each side of the carriage-way. The 
curb-stones should be large and strong, and rise several inches 
above the general surface of the paving, to prevent wheel car- 
riages from getting on to the foot-way; and they should, likewise, 
sink into the sole below the bottom of the paving stones. The 
sole being prepared and finished, is to be covered evenly and 
uniformly, by about two inches of fine hoggin, or coarse sand, 
for the purpose of receiving and bedding the stones, which are 
now laid on in regular courses, guided by a line strained across 
the road. In granite paving, the greatest length of the stone is 
laid across the road, but in boulder paving, the opposite direction 
generally prevails. The workman, w^ho places the stones, which 
are brought to him by an assistant, has no other tool than a ham- 
mer about a foot long, one end of which has a broad ordinary face, 
and the other is shaped like a spoon or scraper. With the scraper 
he draws a small quantity of sand or hoggin, or displaces it, so 
as to form a bed that will fit or suit the bottom of the stone now 
placed upon it, and forced into as close contact as possible with 
the stones previously laid. That done, he uses the other end of 
the hammer to drive a quantity of the sand round the stone, and 
into the interstices between one stone and another, and these 
operations are repeated until the whole road is paved or covered, 
when the entire surface is rammed, or beaten down by a number 
of men who are employed for the purpose, and who use heavy 
rammers or beetles of wood, with w hich they beat the surface of 
the stones until no further sinking or subsiderice can be produced. 
The surface is now covered with fine sand, which is raked or 
moved about, in order that it may fall into the joints or inter- 
stices, w^hcn the paving is considered as finished. Large granite 



ON THE CONSTRUCTION OF ROADS. 245 

paving, including the stones, gravel, labour, and all expenses, 
costs half a guinea, or about two dollars and a half, the square or 
superficial yard, in London. There appears to be some difference 
of opinion as to the form to be given to paved streets, the Eng- 
lish and American fashion being to form a channel or water- 
gutter on each side of the road. The French make but one 
channel, and place it in the middle of the street. The Spanish 
adopt the same plan, but they have a deep drain, covered with 
large stones, running along the centre of the street, between 
which, the water gets into it. In the French form the streets 
frequently cannot be crossed for water, while two channels di- 
vides the stream into two halves, and is certainly preferable. 

447. Paving is not only used in the streets of towns, but is 
frequently resorted to in roads of great traffic; but in such places, 
its expense precludes the possibility of extending it over the 
whole width of the road, and it is, therefore, usually confined to 
the central part, and made eight or nine feet wide for a single 
track, or sixteen feet wide to admit of carriages passing each 
other. The two sides of the road are gravelled in the usual man- 
ner, and when so formed, they are generally called summer and 
winter roads. The gravelled part being used in fine and dry 
weather, and the paved part, when it becomes bad. In forming 
these roads, a general curve or convexity should be given to the 
whole road, in order that the water may run from the two sides; 
and long curb stones should be placed at the two edges of the 
paved part, to maintain the outer stones in their proper places. 
These curbstones must not, however, rise as in other cases, either 
above the paving, or above the road, but should be exactly level 
with them. If they are at all elevated they produce a concus- 
sion whenever a loaded carriage goes on to, or leaves the pave- 
ment, which in one case disturbs the paving stones, and in the 
other, forms hollows in the inner edges of the gravelled part 
which hold water, and will, in time, undermine the pavement. 
The paved centre should have a crown rising higher than the 
general crown of the road, or have a greater convexity, falling 
into the general curve, at the two lines of curbstones. On good 
and hard ground, a summer and winter road is often made with- 
out having recourse to paving at all; but the middle part of the 
road is gravelled for bad weather, while the two sides or wings 
consist merely of the natural soil. 

448. No definite rules can be laid down for the measurement 
of road work, further than that whenever excavation is required 
for it, it is treated like other work of the same kind, and esti- 
mated in cube yards, except when the cutting or forming is very 
shallow, and then it is measured and paid for by the superficial 



246 ON THE CONSTRUCTION OF ROADS. 

yard. Gravelling is also occasionally clone by the superficial 
yard, but it is a very unsatisfactory method, often leading to 
disputes. The best and most unequivocal manner of making an 
agreement for the digging and supply of gravel, is by the cube 
yard or bushel, and the best mode of measuring it, is to have the 
bodies of the carts made or marked to a certain size, and seeing 
that they are filled to that mark; or a strong box with handles, 
but without a top or bottom, is made of an exact cube yard, or 
half yard dimensions. It stands on the ground and may be fill- 
ed, and that done, is lifted up to discharge the contents, and 
removed to another spot to be filled again. 

449. In large cities, and their vicinity, the streets and roads 
are frequently watered in summer, to cool the air and prevent 
the dust from rising. This is done by hose pipes from the 
water-works, when towns possess them, or by carts formed for 
conveying water, which is distributed through many small holes 
where the water cannot be otherwise conveyed. Road watering 
contributes much to the comfort of travellers in hot and dry 
weather, and if done in moderation is not objectionable. It is, 
however, often carried to excess, and then after what has been 
said on the importance of keeping roads dry, it is needless to 
repeat that it is very objectionable and is always disapproved by 
those who have the charge of superintending and repairing roads. 

450. The paving of footpaths at the sides of streets or roads, 
has little connexion with the business of the Engineer, but as the 
object of this work is improvement as well as instruction, and 
the English method of maintaining turnpike roads has been ex- 
plained at some length, a contrast of the English and American 
mode of managing such paths, may not be considered wholly 
irrelevant. In the cities of America, they are usually paved 
with bricks, a material by no means objectionable, provided the 
bricks were of uniform goodness, and laid at the same time; but, 
if some are good and hard, while others are of a worse descrip- 
tion, the pavement which has usually an equal degree of wearing 
from one end of a street to the other, cannot fail to get into 
holes and inequalities that hold and retain water. Moreover, the 
rain from the tops of the houses after being conducted down the 
pipes, is discharged into shallow gutters on the surface of the 
path, thus rendering it much more wet than it otherwise would 
be. The central street, or carriage-way, is taken charge of and 
repaired by the corporation or ward authorities, and is therefore 
uniformly of the same workmanship and materials, but the foot- 
paths between the front of a house and the curb stones, which 
ought to be equally well attended to, are left in charge of the 
householder, who may happen to be poor or rich, particular about 



ON THE CONSTRUCTION OF ROADS. 247 

the appearance of his premises, or negligent, consequently under 
such arrangement uniformity of pavement cannot be expected. 
If the middle of the street is kept in good order by the public 
functionaries, why should this privilege be denied to the side 
walks? If the whole was under the same control and manage- 
ment from house front to house front, as is the case in England, 
the paths of a whole street would be laid down or be repaired 
at once, by the same workmen, with uniformity of level, of 
material, and of appearance; a circumstance that can never be 
expected while the control is left in the hands of so many in- 
dividuals. This, and not permitting any of the roof water to 
be discharged on the paths, and substituting flag stones, or large 
flat paving stones, each of which covers at least a yard of sur- 
face, constitute the only difierence between American and Lon- 
don pavements. The latter city has large and deep sewers or 
brick drains from four to six feet diameter, running through 
the centre of every street, at a depth of five or six feet below 
the pavement, and every house has its drain running into this 
common sewer, by which all slops, refuse water, and ofial, from 
the houses, are carried away at once without being seen, and the 
inhabitants are prohibited by penalty from discharging any thing 
on to the surface of the streets. The rain water from roofs is dis- 
charged in the same unseen manner. But towns notpossessingsuch 
sewers, might convey the rain water from the descending pipes 
into small drains constructed immediately beneath the pavement, 
and conducting it as far as the curb stones, from which it would 
be discharged into the carriage-way channels, without annoying 
foot passengers. The same thing is frequently done by cast-iron 
pipes of a peculiar construction, which is shown in section at 
Fig. 116, Plate IV. The pipe is of three or four inches di- 
ameter, according to the quantity of water to be discharged, and 
should be of a length equal to the breadth of the pavement, to 
avoid joints. They only difier from other pipes in having a 
longitudinal slit or opening of about three-fourths of an inch 
wide, as shown at «, running the whole length of the pipe, for 
cleaning it out, and in having the side of the pipe in which this 
opening occurs flat, instead of round. When the pipe is used, 
this flat side is placed upwards, on a level with the pavement, 
which abuts close against, as shown in the figure, and by this 
means the pipe is fixed and prevented turning round. The open- 
ing is so narrow that no inconvenience arises from its existence, 
and it is left for the introduction of a small iron scraper of the 
form shown at h in the same figure, which being thin, may be 
introduced through the slit, and being then turned a quarter 



248 ON THE CONSTRUCTION OF ROADS. 

round it nearly fits the cavity of the pipe, and removes any de- 
posit, or obstruction to its discharging end without difficulty. 

It seldom happens that a road can be continued for any great 
distance, without the necessity of constructing culverts for the 
conveyance of water under it, or bridges for passengers and car- 
riages to pass over rivers or streams, and it may therefore be ex- 
pected that something should be said on these subjects; but as 
their formation embraces principles of construction not yet treat- 
ed of, we must defer any observations on these heads until these 
principles have been explained. 



CHAPTER VIII. 

ON BUILDING MATERIALS. 

Section I. — Of Stones and Bricks. 

451. Under the general denomination of building materials 
are comprehended all the various substances made use of in the 
formation of buildings, machinery, and constructions of every 
kind; and the object of the present chapter is, to enumerate some 
of the principal of these, to point out what they are, how they 
are procured, and converted into such forms as will render them 
available; and that done, the succeeding chapter will investigate 
their value and forms, by an examination of their strength and 
durability, and the purposes to which each are particularly suit- 
able. 

452. Many of these materials are produced by nature in a 
state fit for immediate use, such as the several varieties of stone 
and timber; while others require operations of art and manufac- 
ture to render them available, of which bricks, lime, the metals, 
and many other things that might be mentioned, are examples. 
On this account these materials have been called natural and arti- 
ficial, but this distinction is unnecessary; and in proceeding to 
describe them we shall, therefore, follow the order of their unity 
in preference to any other arrangement. In erecting a building 
the first thing to be attended to is the foundation and external 



ON BUILDING MATERIALS. 249 

walls, which are usually of stone or brickwork. The materials 
that compose them will, therefore, be the first object of attention. 
The floors and roof require timber, which will be next consider- 
ed, and as they often require the assistance of iron or other 
metal to assist their union and promote strength, the metals will 
close this division of the subject. 

453. Mineralogists and geologists enumerate a great variety of 
stones, but the Builder and Engineer recognise but three great 
divisions, which are known as free-stone, slab-stone, and rub- 
ble-stone, so denominated merely from their hardness and the 
nature of their natural fracture. Of each of these there are many 
varieties. 

Free-stone is always granular in its texture, although the grains 
may vary in magnitude, and are even occasionally crystalline in 
their form. The name of this stone is derived from the freedom 
with which it may be worked or wrought into any particular 
form; for all the varieties of this stone have no disposition to 
break in one direction more than another, and one of its leading 
characteristics is, that although durable against weather, yet it is 
so soft that it may be sawed by the proper stone-cutter's saw, or 
may be worked into any desired form by the chisel and mallet. 
This variety of stone is, therefore, constantly resorted to for all 
ornamental purposes, such as carving the capitals of columns, 
friezes, and mouldings, as well as for the building of stone 
walls whenever it is necessary that their surfaces should be 
smooth and handsome. 

454. Marble, in all its varieties, ranks as the first or most 
valuable of all the free-stones, on account of the large masses in 
which it is formed, its great durability, its not absorbing vi^ater, 
the ease and certainty with which it may be worked even into 
the finest ornaments, the compactness of its grain and its hard- 
ness, which enable it to receive a high and permanent polish, 
and its not being sensibly affected by heat and cold, or any fluc- 
tuations of season. Marble is a carbonate of lime, and when 
quite pure, is perfectly white, but it is very rarely found without 
dark-grey streaks, and is often beautifully coloured with various 
tints throughout its whole substance, when it is called streaked 
and variegated marble. The very finest pure white marble comes 
from the island of Paros, and has long been celebrated both by 
sculptors and poets under the name of Parian marble, being the 
stone of which the finest Grecian statues were formed. The 
next in point of quality is the Carrara marble, equally pure and 
white, but differing in its grain. These varieties of marble are 
called statuary marble, being used exclusively for carving statues 
and the most delicate ornaments, and is so high priced that it is 

33 



250 ON BUILDING MATERIALS. 

seldom used by the builder except in the most costly chimney 
pieces or other ornamental works. 

455. Alabaster is a white stone, very much resembling statu- 
ary marble in appearance, but it is a sulphate instead of a car- 
bonate of lime, and therefore not a marble, besides which, it is so 
soft that it may be cut by the common hand-saw, or a knife, is 
very brittle and not durable in the open air, consequently unfit 
for the builder, and it is only used for articles of internal orna- 
ment. 

456. Marbles and many other articles in this class of building 
materials, have no names except such as are derived from the lo- 
calities where they are found, and this renders them difficult of 
description and identification, unless the character and appear- 
ance of the stone is known. Thus we have Kilkenny marble, 
from a place of that name in Ireland, which is exactly the re- 
verse of statuary marble, though equally fine in its grain and 
good in its quality, but it is of one uniform intense black colour, 
without any variegation. 

Lumachella marble, from Italy, is equally black, but is inter- 
spersed with veins, shells, and organic remains, which when cut 
and polished, give it a very handsome appearance. 

Florentine marble, from Florence, is reddish-brown, and pre- 
sents an appearance of the ruins of old castles and towns, and on 
this account it is sometimes called ruin marble. Some varieties are 
named after their appearance. Thus dove-coloured marble speaks 
for itself. Black and gold marble, (used for table tops,) is from Italy, 
and consists of a fine black ground, with rich brown and yellow 
veins and spots running through it, which, at a distance, appear 
like gold. Breccia marble consists of angular fragments of va- 
rious coloured marbles united together by a calcareous cement, 
and is often very beautiful. Sienna marble is of a rich bufi' co- 
lour, variegated by difierently coloured streaks. That splendid 
marble, called Verd Antique, or Ancient Green, was much used 
by the ancients in their ornamental works, and is an elegant as- 
semblage of various green tints, from almost black to a colour of 
great brilliancy, and is scarce and high priced, when in large 
slabs. It is called Egyptian marble in this country. It is not, 
properly speaking, a marble, or at any rate a carbonate of lime, and 
is hardly entitled to the name of a free-stone, on account of its 
being very brittle and refractory. But it yields to the saw, so as 
to be cut into slabs, and with care may be worked into orna- 
mental forms. Its mineralogical name is precious serpentine, 
and it contains a large proportion of magnesia, iron, and manga- 
nese; and, like most of the preceding stones, is only used for in- 
ternal decoration. 



ON BUILDING MATERIALS. 251 

457. The common marbles that come more immediately into 
the hands of the builder, are the impure or streaked white, and 
the dove; and these are very abundant in many of the northern 
states of America, and are very extensively used in all the best 
buildings, giving them a stability and beauty not to be met with 
in any other part of the world, Italy alone excepted, which has 
always been celebrated for the abundance and beauty of its mar- 
bles. 

458. Next to marble, in point of utility, firmness of grain, and 
durability, may be ranked the fine grained white sand-stone, 
which consists of fine siliceous or flinty sand, held together by a 
peculiar natural cement, that binds the whole into a solid, uniform, 
compact mass, but still is so small in quantity that it cannot be 
perceived between the grains, so that the whole stone appears as 
if formed of fine sand. On account of the scarcity of marble in 
England, this stone is alone used for all the best buildings, and 
as it is found most abundantly in the Portland rocks, on the south 
coast of the island, it is universally known throughout that coun- 
try under the name of Portland stone. When clean it is very 
nearly white, will bear fine carving, and it is very strong and 
durable, not being at all affected by water, frost, or exposure to 
air. It will not take a polish like marble; but as this stone is 
hardly ever polished on the exterior of buildings, the one stone 
can hardly be distinguished from the other, except on close in- 
spection. St. Paul's Cathedral, the Monument, the Royal 
Palace, and all the fine buildings of London, are built of this 
stone. A stone very nearly similar in appearance to it, is found 
in the northern states, and is called North River, or Hudson's 
river stone; but, as marble is so plentiful in this country, it does 
not appear to be much used, and the author has had no oppor- 
tunity of examining its qualities, to ascertain if it is as good as 
Portland stone. 

459. There are other varieties of free-stone, but they are very 
soft, particularly when green, a term applied by workmen to 
stone fresh from the quarry; for almost all stones either become 
hard by age and exposure to the atmosphere, or they slack, or 
become friable, and sometimes even drop to powder; and, of 
course, this last class is wholly unfit for building purposes. 
A very useful stone, called by mineralogists ooilite^ from its 
similarity in appearance to the roe of a fish, makes an exten- 
sive formation nearly through the middle of England, beginning 
in Somersetshire, and taking a north-east direction for about 150 
miles. It has a yellowish-white colour, is wholly calcareous and 
granular, its grains sometimes being as fine as sand, and, at 
others, hollow and as large as peas, when it is called pea-stone. 



252 ON BUILDING MATERIALS. 

They are united by natural calcareous cement, which is quite 
visible to the naked eye; but the fine grained stone is alone used 
for building, and the whole city of Bath is built with it, on which 
account it has, very generally, obtained the name of Bath-stone. 
When new, it is so soft that it is cut into any required form by 
a common carpenter's hand-saw, and is also worked by the chisel; 
notwithstanding which, and its being absorbent, it is not affected 
by weather, and hardens and preserves its form remarkably well. 
It is on this account considered valuable, for it may be worked 
very cheaply, and produces a handsome appearance. It is be- 
lieved that it does not exist in this country. 

460. Another soft stone is used in the ferruginous districts of 
England, called ferruginous sand-stone. It consists of coarse or 
sharp silicious sand cemented together by oxide of iron. It has 
a dark reddish-brown colour, is soft at first, but becomes very 
hard by exposure to air. It is common in Bedfordshire and the 
internal counties, and stone bridges, having arches of consider- 
able span, are built with it, and stand well. 

461. Soap-stone is another variety of soft stone which exists 
abundantly in Pennylvania, and may be readily cut to any form: 
when good, it withstands very violent degrees of heat, and is 
therefore valuable for building furnaces and fire-places, but it is too 
soft to be used for other building purposes. 

462. One of the hardest, best, and most durable stones for 
building is granite, and its varieties, which is placed last in this 
list, from a feeling of doubt as to whether it should rank among 
the free or refractory stones. It is so hard as to bid defiance to 
the saw, and almost to the chisel, but still it can be worked to 
any desired form, and to a fair, but not smooth face, and has no 
tendency to split into laminae, and for these reasons it may be 
considered as a free or workable stone. True granite is a com- 
pound of quartz, felspar, and mica, not chemically united with 
each other, but so closely aggregated, that when the grain is fine, 
it is difiicult to distinguish one from the other; but, if coarse, as 
at Haddam in Connecticut, the three materials appear almost 
distinct. In this stone the quartz may be said to be imperish- 
able. The felspar is durable, but still gradually decomposes by 
exposure, and the mica, which is always soft, and of no import- 
ance as to the value of the stone, soon gives way and disappears. 
The kind of stone now so much in demand for supporting store 
fronts, and of which several buildings have been constructed in 
the northern cities, though called granite, is not a granite, inas- 
much as it is without mica, and often contains little or no quartz, 
both of which are essential to the formation of the real granite. 
All the specimens the author has examined, are what mineralo- 



ON BUILDING MATERIALS. 253 

gists call sienite, a stone consisting of felspar and hornblende, 
This stone is commonly called Boston granite, but he is inform- 
ed it comes from quarries at Quincey, to the south of that city, 
and is very convenient for sea-carriage. It is got out and sold 
at from forty-five to sixty cents the cubic foot, increasing in 
value in proportion to its magnitude. It is harder and more 
difficult to work than real granite, and, in the writer's opinion, it 
is one of the best stones he has ever met with for building, where 
strength, neatness, and he believes durability are required. 
Neatness is here spoken of, because the stone is too hard to be 
worked into richly carved and florid ornaments; and, as to its 
duration, little doubt can be entertained, but this point cannot be 
decidedly known until it has stood the test of exposure to wind 
and water for at least a century. Its dark colour may be object- 
ed to by some; but the northern district produces a great variety 
of colours, from very dark to almost white, which is the charac- 
ter of the granite from Hollowei in Maine, but the white stones 
do not appear so compact and good as those of darker hue. The 
Quincey granite it is believed would make excellent street pave- 
ment, and even the small chips might be used with advantage 
for M^Adam roads. 

463. Slab stone, is stone of a decidedly lamellar construction, 
and appears to have been formed by the successive deposition of 
layers of hard material, one upon the other. The character of 
this stone is, that it splits into thin and parallel plates of greater 
or less thickness, with considerable ease; and in general possesses 
great tenacity or strength, in the direction of its laminae, and 
most varieties admit of being cut transversely by the saw. So 
far it resembles a free stone, but still it cannot be cut into any 
desired form, the capital of a column for instance, for it is re- 
fractory and brittle except in the direction of its natural joints, 
and at these it would separate under the vibrations produced by 
the mallet and chisel, if attempted to be worked, or if worked 
by great care and patience, the parts would separate at these 
joints, by exposure to time and weather. For the same reason, 
if this stone should be used in building, with its natural joints 
set vertically, the outsides would scale off*, and the stone would 
decay and fall to pieces unless it happened to be supported 
in the inside of solid work. It must therefore be always used 
with its joints in a horizontal or nearly horizontal position, if 
it is subjected to any load or weight, and then it will prove very 
durable. On this account, such stone is always used for the 
foundations of high and heavy walls, where it is advantageous on 
account of its being flat and smooth, and its large dimensions 
covering a great portion of the ground. It is also very good for 



254 ON BUILDING MATERIALS. 

paving the side or foot-paths of streets, or the bottoms of cellars 
or warehouses, for making the floors or platforms of balconies 
or verandahs projecting from buildhigs, for capping or coping 
walls, or making the treads of stairs, for covering roofs, and many 
similar purposes. All the varieties of slate rank under this 
variety of stone, and some of them are very large, strong, and 
handsome, running to lengths of twenty feet or more, by three 
feet wide, and from two to six inches thick, so that they are ad- 
mirably calculated for floors of balconies, which are very com- 
mon in the fronts of European houses. The Yorkshire paving 
with which the footways in England are alone paved, is of the 
same character, but is silicious grit stone, containing alumine, and 
forming a very hard and tough stone that splits into laminae of 
from two to six inches in thickness, and is very difficult to cut 
or work; it has the property of never wearing to a smooth or 
polished surface, which is a great advantage in foot pavements. 
It is found above the surface of the coal seams or veins in the 
northern part of England, and is transported, squared, and laid 
down in the streets for twenty-eight cents the superficial foot. 
Some stones of this description, which were considered a curiosity 
from their magnitude, were laid down a few years since near St. 
Pancrass church. They hold the enormous quantity of nine and 
twelve yards superficial in each stone, without a joint, having a 
width of three yards, by a length of three and four yardsj but 
when so large, they must be much thicker than ordinary, and 
are more expensive. 

464. The mica slate of this country is the nearest approxima- 
tion to the same kind of stone, unless, as is most probable, the 
same variety of stone may be found in the coal regions now so 
extensively worked. 

465. Shingles are unknown in Europe, or at least never made 
use of for covering buildings; sheet metal, and slates or tiles, being 
the only materials used. Slating is the most common covering 
for the best buildings, on account of its durability, its lightness, 
its appearance, and its efiectually resisting the action both of fire 
and of water from without; and these slates are the natural slate- 
stone split into laminae, varying from an eighth to half an inch in 
thickness, according to the size of the slate made use of, and 
from which they derive their names. 

466. A very variable compound stone called gneiss, which is 
a variety of granite, generally containing hornblende, in addition 
to the usual materials, assumes the lamellar formation, and may 
be divided into plates fit for paving or placing under foundations, 
but is not so regular and even as the varieties before noticed. 

467. Rubble or rough-stone, comprehends all such stones as, 



ON BUILDING MATERIALS. 255 

from their hardnesss, cannot be sawed, and from their brittleness 
or irregularity of grain, combined with hardness, resist the chi- 
sel and all attempts to reduce them to regular forms, except by 
grinding and the lapidary's art, which is too slow and expen- 
sive to be applied to building purposes. Flint stones, the trap 
rock formations, compact limestone, buhr-stone, of which French 
mill-stones are made, and porphyry, which is a variegated mix- 
ture of felspar and quartz, are of this description, notwithstand- 
ing the latter can be worked with great labour and expense, for 
the ancients formed columns and other ornaments of it, to which 
they gave a high polish. At present, such stones are only used 
for constructing rough or rubble work under foundations, or for 
filling in walls of more than ordinary thickness, and backing or 
strengthening them in places that are concealed from view. 

468. Large blocks of stone are only to be procured in rocky 
places, and the openings or excavations made for obtaining them 
are called quarries. When once a quarry has been opened and 
is found capable of yielding a large quantity of stone, the quali- 
ties of which have been tested by long use and experience, it be- 
comes a very valuable property, of which the Quincey works, 
near Boston, the marble works at East Chester, the granite quar- 
ries at Aberdeen, and those of slate in Wales and Westmoreland 
afford ample proof. From the weight of the material produced, 
a quarry is unworthy of prosecution unless it has the advantage 
of water conveyance, and of a rail-road for transporting the ma- 
terial to the water's edge, and even with every advantage it re- 
quires considerable forethought and skill to work it with con- 
tinued advantage. The Engineer may be so placed that he 
cannot have the advantage of the public quarries, and may be 
obliged to raise his own stone, in doing which the following ob- 
servations may be useful. A quarry is seldom a deep excava- 
tion like a mine, but consists of working a way into the side of 
a hill. One of the first things to attend to, therefore, is not to 
begin the work too low, so as to get the quarry into a hole, from 
whence it may be very troublesome, dangerous, and expensive 
to raise large masses of stone, but a road leading into it should be 
formed and maintained with as gentle a slope as possible, in order 
that horses may draw the stones up as produced. It is better in 
the first instance, to so arrange as to deliver the first stones ob- 
tained, down hill, instead of having to raise them. But it 
must be kept in mind, that the elevated stone, and particularly 
such as outcrops and is visible; and has been exposed to the air, 
perhaps for centuries, is never so good and sound as that which 
is hidden or has been protected; and pressure also seems to im- 
prove the formation of stone, for that which is deeply situated in 



256 ON BUILDING MATERIALS. 

the quarry is generally more hard, compact, durable, and better 
in every respect than that found near the surface, which is ten- 
der and friable. On this account it may be necessary to work 
downwards, but this should be done gradually and with caution. 
The first operation should be to remove the incumbent soil 
(which is called uncallowing) to such an extent as will expose 
the extent of the masses of stone fairly to view. They are called 
masses, because although the whole rock may seem to be but one 
mass of stone, yet on closer inspection it will be found, in almost 
every case subdivided by natural joints and fissures, too small, 
perhaps, even for the introduction of a common nail, but in which 
the stone has little or no natural adhesion; and consequently, at 
such places one block w^U readily part from another, without 
fear of breaking either of them, if the operation is conducted 
with due skill and care. The horizontal, or nearly horizontal 
joints or fissures, will be seen without difficulty from the front, 
and it seldom happens that they are more than from one to four 
feet asunder, or one below the other. Vertical fissures do not 
always exist, but if they do, they will be just as obvious as the 
others. Having found these, the top of the stone must be search- 
ed (first moving all that is above it) for the fissure in a nearly 
vertical position that corresponds with the front, and should this 
be found, the entire block of stone that can be obtained in one 
piece will be seen. The two end blocks that are contiguous to 
it must now be examined in the same way, in order to deter- 
mine which of the three blocks shall be sacrificed: for the great- 
est difficulty is to get out the first block, on account of its being 
tightly wedged or jammed in by the end ones. One or other 
must, therefore, be broken, either by a short and heavy miner's 
pick-axe, or by blasting with gunpowder, or by gads and the 
hammer; the gad being a thick wedge of hard steel that is held 
in its proper position, about four or six inches from the fissure, 
by the two hands of one workman, while it is powerfully struck 
upon with a sledge-hammer by another, until a sufficient quantity 
of stone is cut awa}^, to permit the stone that is required, to be 
shifted or moved in a sufficient degree by small wedges driven 
behind it, under it and on the undisturbed side of it, to cause it 
to become detached from its natural bed, when it will be ready 
for removal: and this, it might be supposed, would be effected by 
the application of strong iron crow-bars or levers to it in the first 
instance, so as to raise it sufficiently to get hard wooden rollers 
under it, by which it might be transferred to a platform, inclined 
plane, or truck* prepared to receive it, and such accordingly is 

* A truck is a more than ordinary strong four-wheel carriage, to run on rail 
or common roads. It has a strong platform but no sides, and is used for con- 
veying very heavy single stones or masses of cast iron. 



ON BUILDING MATERIALS. 257 

the method adopted for the removal of all large stones that come 
up with broken or irregular sides and edges, and which will, 
therefore, require to be scahhled or rough dressed by a stone- 
mason, before they can be delivered or used. But as the value 
of all large and fine stone is much enhanced by its magnitude, 
by having no cracks or flaws in it, and by having its faces as flat 
as possible, and its angles sharp or unbroken, so that the mason 
in working it need not cut much to waste, the introduction of 
wedges or levers of sufficient strength to raise its weight, could 
not fail to destroy its figure by breaking away the edges, and it 
is, therefore, found more advantageous to lift it from above, than 
to raise it from below, or at any rate, to have both forces in ope- 
ration at the same time, so as to cause the lifting action to di- 
minish the weight. This is effected by a very ingenious device 
well known to every mason under the name of a Lewis. If a 
stone is not lifted in the quarry by a lewis, it is sure to be so 
treated by the mason in setting it in its place when worked and 
finished, since this is almost the only way in which a heavy 
stone could be raised, lowered, and moved about with precision 
in any direction, without fear of injury to its sharp edges and 
angles. 

469. The lewis consists of three pieces of strong iron, formed 
and held together by a shakle and screw bolt, as shown at 
Fig. Ill, Plate IV., which is a front view of the instrument 
when put together. In the opposite direction the sides are pa- 
rallel to each other, or the pieces are of the same thickness 
throughout, which may be from one and a half to three inches, 
or more, according to the weight of the stone to be lifted. In 
front view, the two pieces c d, c d, are made angular, or to 
spread out so as to be at least twice as thick at the bottom d d as 
they are at c. These thicknesses may be one inch and two inches, 
and the pieces are both alike. The middle piece is parallel, or of 
the same size from top to bottom, and may be two inches thick; 
then, according to the above dimensions, when the three pieces 
are put together, as in the figure, the distance across from c to c 
would be four inches, and from d to d six inches; but on taking 
out the screw-pin, the central piece e may be withdrawn, and 
the two outside pieces brought close together, when the distance 
from dio d will be reduced to four inches; so that if a dovetailed 
cavity is sunk in the middle of the upper side of a large block of 
stone, four inches wide at the top and spreading to six inches at 
the bottom, and deep enough to take in the whole lewis, which 
may be from four to eight inches long, the two pieces c d may 
be separately introduced into that hole; and then, on putting the 
middle piece between them, with the bolt and shakle attached as 
33 



^58 ON BUILDING MATERIALS. 

in the figDre, the instrument will occupy the whole cavity, and 
no force can withdraw it from the stone without tearing away 
the upper part of the dovetail. The lewis, therefore, becomes a 
strong handle, by which a stone may be lifted up perpendicular- 
ly by a force applied above it. That force is produced by a pair 
of blocks and fall, or system of pullies, the end of the rope to 
which the power is applied being connected with the cylinder of 
a portable winding machine called a crab, being a series of cast 
iron cog-wheels and pinions, arranged in a proper frame for gain- 
ing mechanical power, and much used in quarries, and the con- 
struction of heavy masonry. The upper block requires to be 
attached to a crane or support of some kind, for sustaining the 
load, and the expedient resorted to in quarries is the same as that 
constantly adopted in ships for raising heavy goods. It is mere- 
ly a boom or strong beam of timber, fixed as nearly perpendicu- 
lar as possible, with its upper end and block over the stone, and 
its lower extremity so secured as to be incapable of slipping. 
The crab is placed near the foot of the pole, in order to make 
the draught of the rope as nearly coincident as possible with the 
direction of the pole, the top of which is sustained in the requir- 
ed position, or may be moved a short distance from it by three 
strong ropes called gui/ ropes or guides, meeting in opposite di- 
rections and terminating below in blocks and falls, firmly at- 
tached to the ground, trees, or neighbouring rocks, so that by 
tightening one and slacking the other at the same time, the posi- 
tion of the top of the pole may be shifted for taking up a stone 
in one place, and lowering it down in another, or on to a truck 
for conveyance. If the stone is very heavy it will be safer to 
use two poles united together at their tops like the letter A. By 
giving them considerable inclination while the stone is taking up 
from its bed, and then making them stand more erect by hauling 
in the guy ropes, a stone may be lowered on to a truck between 
the two poles. 

470. When the natural vertical fissures before spoken of do 
not occur in blocks of stone, or whenever it may be desirable to 
raise smaller blocks than they would produce, fissures or cracks 
must be produced artificially, and this is usually done by drill- 
ing a line of holes into the stone at regular short intervals, in 
the straight lined direction in which the separation is required; 
a row of conical steel points, rather larger than the holes, are 
then set one into each hole, and a number of men strike with 
hammers simultaneously upon them, which, if done equably, 
never fails to produce a separation of the piece of stone in the 
direction required. If the stone is found to cleave easily, dry 
wooden pegs, previously cut, larger than the holes and driven in 



ON BUILDING MATERIALS. 259 

the same way, will answer the purpose, and is most frequently 
resorted to for obtaining blocks both of granite and marble in 
this country. Should the wooden pegs fail, a bank or wall of 
clay must be built around them capable of holding water, and on 
filling this, so that the Vv^ater can sink into the pegs, they will swell 
with such force as never fails to separate the mass, provided 
hard and perfectly dry wood has been used. 

471. The drilling of hard stone cannot be effected by ordinary 
revolving drills. The drill made use of is a steel cold chisel, 
eighteen inches or two feet long, its breadth being equal to the 
diameter of the hole to be produced, and its edge being double 
bevelled, and not too acute or sharp. It is held by a workman 
over the place where the hole is to be made, and struck with a 
hammer in the other hand, or by a separate man when the stone 
is very hard, and the hole large. Between each blow of the 
hammer the chisel (called a drill) is turned partly round, and is 
kept revolving or moving backwards and forwards, so that two 
cuts or blows never come in the same direction, but make a se- 
ries of indentations like a star *, and the powdered stone falling 
to the bottom, is taken out by a kind of screw formed spoon 
like a screw auger. In this manner holes are made more speedi- 
ly than might be expected, and they are usually paid for by the 
inch, according to their size and depth. 

472. The process of blasting rocks by gunpowder requires the 
same holes to be drilled, but for this purpose they must be deeper 
and larger than for splitting rocks. From half an inch to three- 
quarters diameter, and six or eight inches deep will, generally, 
be sufficient for the splitting holes, while eighteen inches to two 
feet is a common depth for those used in blasting, and they should 
not be less than an inch in diameter. The gunpowder, for con- 
venience of introducing it, is sewed in a linen or flannel bag, or 
cartridge, having a train that is confined in a straw or small reed; 
or, if the hole is wet, the cartridge is made of tin, with a fine tin 
tube to contain the train. Having introduced the powder, dry- 
sand is put upon it, and rammed down, when the remainder of 
the hole is filled with sand a little moistened. This is called, 
tamping a hole. Some wild-fire, or powder kneaded with water, 
or slow match, made of paper, or old linen, soaked in saturated 
solution of nilre, is made to communicate with the train, and this 
must be so arranged as to give the person firing it, time to retreat 
before the powder explodes, as fragments of the stone are fre- 
quently dispersed with such violence as to be very dangerous. 
The most hazardous thing in shooting a hole, as miners call this 
operation, is when, by improper fixing of the match, the whole 
charge explodes the instant the fire touches it, or where it hangs 



260 ON BUILDING MATERIALS. 

fire, or is so long before it explodes that the workman imagines 
tlie match has been extinguished; and, perhaps, goes to inspect it 
at the very time when it explodes. From both these causes very- 
serious accidents have occurred, and no one ought to approach a 
hole after the match has been lighted, until such a period has 
transpired as must render an explosion impossible. Dr. Hare, 
of Philadelphia, has been engaged on some experiments on the 
means of producing ignition of the gunpowder by voltaic elec- 
tricity, conducted through long wires, without the intervention 
of a slow match, so that the ignition shall take place instantly, or 
not at all; and such a process, respecting the eiFicacy of which 
there can be no doubt, will confer a great obligation on such as 
are engaged in this business. 

473. As marble and granite have always to be transported, 
unless used upon the spot where they are produced, it may be 
useful to remark, that fourteen cubic feet are considered as equal to 
a ton weight, on which account a considerable loss frequently 
accrues to the purchaser; for the cubic quantities are taken by 
weight, to determine the freight, instead of by measurement; and 
as the above proportion is not a true one, the cubic feet rarely 
measure to what is marked upon the stone, or what they are sold 
for, particularly when it is hard, good, and compact. But lighter 
and more porous stone will, on the contrary, yield more than 
fourteen feet to the ton. 

474. Next in order to natural stone comes brick, which is an 
artificial or manufactured kind of stone, most extensively used in 
vast building operations. The brick offers some advantage over 
stone, arising chiefly from the expedition and ease with which 
the work may be conducted. No stone can be obtained from the 
quarry of a shape fit for use in close jointed work, without the 
tedious process of sawing or cutting it to a fair face; and as stones 
are large and heavy, there is great loss of time in transporting 
them, and raising them to their positions in the wall. Stone can- 
not always be procured, owing to local circumstances, but there 
are few positions in which brick-earth cannot be obtained within 
a few miles; and bricks are very portable, are square and ready 
formed, and if good, and used with good mortar, will produce a 
better and more durable wall than could be produced by small 
blocks of hard stone. The stability of a stone wall, with straight 
joints, depends more on the weight and magnitude of the stones 
than on the adhesion of the mortar. For as the harder stones are 
not absorbent, the mortar will not adhere to their surfaces and 
produce union; while, from bricks being of an opposite character, 
the brick and mortar, after a short time, become one, and their 
adhesion is so strong that it is difficult to separate them. 



ON BUILDING MATERIALS. 261 

475. Bricks have, accordingly, been used by all nations from 
the earliest antiquity. The bricks of Babylon, many of which 
bear inscriptions, are known at the present day, and many of the 
admired relics of the ancients, still extant in ruins, exhibit the 
perfection to which the art of brickmaking had arrived in these 
early days. Some of the structuresof Egypt andPersia,the walls of 
Athens, the Pantheon and Temple of Peace, at Rome, and many 
other buildings are constructed of brick. What is surprising, 
however, is that many of these bricks, which have stood the test 
of about 2000 years, do not appear to have been burnt or submit- 
ted to the action of fire, to produce their hardness and durability, 
w^hich can alone be attributed to the extreme dryness and heat of 
the climate in which they w^ere exposed; for these bricks, on 
being soaked in water, crumble to pieces, and disclose straws, 
reeds, and other vegetable matter, from the existence of which 
it is inferred they have never been submitted to any greater heat 
than that of the sun. At a later period all the bricks of the an- 
cients were burnt, and it is these that chiefly remain at the pre- 
sent day. 

476. A brick is nothing more than a mass of argillaceous earth 
or clay, properly tempered with water and softened, so that it can 
be pressed into a mould to give it form, when it is dried in the 
sun, and afterwards submitted to such a heat as shall bake or burn 
it into a hard substance. This method of forming bricks puts a 
limit to their magnitude; for, as the material of the brick is a bad 
conductor of heat, so, if they were made very large, the heat ap- 
plied externally would never reach the inside so as to bake it 
properly, without vitrifying and destroying the outside; hence 
bricks must be confined to such m.agnitudes as will admit of their 
being well and equably burnt throughout. In England, the size 
of bricks is determined by law, and no man can make bricks 
larger or smaller than the prescribed dimensions. This law is, 
by many, considered a hardship, but it was established for a two- 
fold purpose, first, because all bricks made there are subject to 
an excise duty or tax of about a dollar a thousand, which tax 
could not be equalized, unless a size was fixed for the brick; and 
secondly, it enables a person building, to know the exact quan- 
tity of work he can erect for a certain sum of money, and pre- 
vents brickmakers taking advantage by sending out small bricks, 
or making them so large that their insides may not be hard and 
well burnt, a circumstance that would produce unsound work, 
deficient in durability. 

477. This law, as far as regards the determination of the size 
of the brick, the writer is now convinced is good. No regula- 
tion appears to exist in the United States, beyond the custom of 



262 ON BUILDING MATERIALS. 

the place and the caprice of the maker. One man makes a large 
and full brick, and gets a good price for it, because fewer bricks 
will do a given quantity of work. Another sells cheaper, but he 
manufactures a smaller article; and it. frequently happens that 
when a builder cannot get his whole supply from one maker, he 
is compelled to go to another, when probably his size will not 
work in with the first, unless a previous bargain has been made 
as to dimensions. The writer having occasion to use a large 
quantity of bricks, and having consumed the first quantity de- 
livered, had occasion to order many thousands more from a 
stranger^ for which a written contract was made, and on their 
delivery he found each new brick an inch and a half shorter than 
those previously used. On remonstrating, he was told that no 
dimensions had been specified in the contract; that those deliver- 
ed were of the usual size, in that part of the country, and no re- 
dress could be had; notwithstanding it took nearly one-fourth 
more bricks to do the same quantity of work, as would have been 
necessary had they been of the proper, or usual standard size, 
which in London is eight and three-quarter inches long, four and 
three-eighths wide, and three and three-quarter inches thick; 
the intention of these dimensions being, that each brick laid end 
to end, or every two bricks side to side, with the necessary 
quantity of mortar between them, shall make exactly nine inches 
of work; or that four bricks laid one on another, will make a foot 
perpendicular, or twelve courses to the yard. In Philadelphia, 
the general run of bricks is eight and a half inches long, and four- 
teen courses with mortar to the yard perpendicular, thus con- 
suming more bricks and mortar than the English gauge, for the 
same quantity of work. The young Engineer must, therefore, 
not only attend to the quality, but to the size of bricks, when- 
ever he makes contracts for their purchase. 

478. Although clay has been named as the proper material for 
making bricks, yet every clay will not answer equally well. Pure 
clay is quite white, and in burning does not change its colour, as 
may be noticed in tobacco pipes, which are made from it. The 
brown colour of common clay is usually derived from oxide of 
iron, and this causes the brick to assume a red colour when burnt; 
but as red bricks are not approved or used for outside work in 
London, where more bricks are made and consumed than in any 
other part of the world, the brickmakers have contrived means 
of changing their colour in burning to a pale buff, very much re- 
sembling the colour of Bath-stone, and which gives buildings a 
much handsomer appearance, and closer resemblance to stone, 
than would be expected. The mode of colouring is kept as se- 
cret as possible, among the manufacturers, but it is partly pro- 



ON BUILDING MATERIALS. 263 

duced by mixing powdered chalk with the clay, and is, probably, 
greatly dependant upon the firing of the kiln and the fuel used, 
since many bricks that exhibit a beautiful and perfect bufi'hue on 
their outsides, are red and dark within, if broken. 

479. A stiff, tenacious, plastic clay is unfit for making bricks, 
as they generally split and fall to pieces in burning. Brick- 
makers call such clay strong earth, and they prefer what they 
term a Tuitd earth; that is, one of less tenacity, and having more 
the character of loam. When the loamy soil is not found natu- 
rally, it is imitated by adding sand in considerable quantity to 
earth that is too strong. The London brickmakers, in addition 
to sand, constantly add a considerable quantity of breeze to their 
clay, and they assert that it is this material that gives the pecu- 
liar character of colour, hardness, and durability to London 
bricks. This is somevvhat corroborated by the country bricks, 
made without breeze, being red and of a very different character. 

480. To explain the term breeze, which seems to perform so 
important a part, it becomes necessary to say that throughout the 
immense metropolis London, no fuel is used in any of the houses 
but bituminous or blazing coal, very similar to that known in 
this country as the coal from Richmond in Virginia. Every 
house has what is called a dust-hole, in some external part of the 
premises, into which the ashes and refuse of these fires are put, 
and the same place is also a depository for any other offal of the 
house, which must not be thrown into the streets. The parish 
authorities contract with persons having horses and carts to clear 
these dust-holes about once a week or oftener, without any ex- 
pense or trouble to the housekeeper, and the stuff collected is all 
carried to certain fixed depositories on the outskirts of the town. 
Here hundreds of men, women, and children, are daily employ- 
ed in assorting and looking over the mountains of discarded 
treasure thus brought in, and now become the property of the 
contractor; apparently worthless in the eyes of the public, but 
not so in fact, for most of the men who have undertaken this 
business, in conjunction with that of scavenger or street-cleaner, 
have in almost every instance amassed immense fortunes. The 
heaps of soil are carefully raked over, and every atom of them 
passed through several gradations of sifting, with sieves of vari- 
ous fineness. Rags, old iron, metal, bones, and such things as 
are usually thrown away, mixed with the refuse fuel, form the 
aggregate of the mass, and all these things are separated and 
placed in separate heaps. Here the paper-maker gets supplied 
with much common rag for packing-paper. The old iron is re- 
turned to the forge to be manufactured into scrap iron. The 
hartshorn and ivory black manufacturer gets supplied with bone, 



264 ON BUILDING MATERIALS. 

much new and unconsumed coal and cinders are obtained, and 
this furnishes the only fuel with which all the bricks of London 
are burnt, while the small and almost incombustible matter, conr 
sisting of very small cinders, and new coal, fire-dust, decayed 
animal matter, and whatever else may be mixed in the mass is 
breeze. This breeze is mixed with the clay, is in a great mea- 
sure combustible when exposed to the high heat required to burn 
bricks, and it is said to assist the brick in getting red hot through- 
out its substance, and otherwise to improve it very materially. 

481. A great deal of care and trouble is necessary in prepar- 
ing the earth for making good bricks, in order to reduce it to one 
uniform texture, and to deprive it as much as possible of all 
stones that might destroy the form of the brick, by breaking in 
the fire, or becoming vitrified. The bricks of Philadelphia are 
in general so good, that we will describe the process used there 
for making them, and point out where it differs from that pur- 
sued near London. The clay in both places is invariably dug in 
the autumn, and during the winter before frost sets in. The 
ground is divided out into square allotments called spits, four feet 
wide and sixteen feet long, which surface when dug a foot deep, 
furnishes the right quantity of earth for one thousand bricks, and 
of course each foot in depth is equivalent to the same quantity. 
This earth is shifted by barrows to an adjoining piece of ground 
previously levelled to receive it, and sunk a little under the 
general surface to prevent water running off. On this it is work- 
ed, if in a fit state to make bricks, if not, sand is added in suffi- 
cient quantity, according to the judgment of the workman, to 
make it sufficiently short or mild, and at this period the London 
brickmaker adds his breeze, which, answering the purpose of 
sand, it is added in less quantity. It is then cut, slashed, and 
worked with the spade, adding water to it to soften it; and the 
quantity of two spits being added together in one heap, sufficient 
earth to make two thousand bricks is exposed to the frost in each 
heap, and the more severe the frost is, the better incorporation 
will take place. Nothing more can be done with it until spring, 
when the warm weather thaws the heaps, and if the frosting 
has been effectual no lumps will remain, but the whole will be 
converted into a uniformly soft and yielding mass. If too wet, 
the heaps are opened and spread to dry, or if too dry, more 
water is added, before the last working with the tool called tem- 
pering, in order to render the whole mass uniformly smooth; it 
is then pressed and patted down, and covered with boards, cloths, 
or bushes, to prevent the injurious effects of the sun and air, and is 
now ready for the moulder. The moulder works at a table or 
bench in the open air, covered by a shed roof only, to protect 



ON BUILDING MATERIALS. 265 

him from sun and rain, and the clay is brought to him in a bar- 
row from the tempered heap, and is placed by the boy who 
brings it on the left hand end of his table; another boy supplies 
him with dry silicious sand previously dug or provided, and 
placed on the right hand end of the table, and a third boy stands 
in front to remove the bricks as fast as they are formed. The 
mould is formed of mahogany or other hard wood, bound with iron 
for strength, and cased with iron plate on its top and bottom, or 
is sometimes lined with thin iron throughout; moulds have been 
formed wholly of iron, but they are too heavy for expeditious 
work, and cold to handle in early spring. The mould is four 
sides of a box without either top or bottom^ as the moulding 
table forms the bottom, and must be very smooth, on which ac- 
count, and to prevent wear, it may be covered with sheet-iron. 
The moulder first covers his table thinly with sand, and cutting 
off a sufficient quantity of the prepared clay with his two hands, 
finger-end to finger-end, to form about a brick and a quarter, he 
kneads it on the table, by pressing on it with the palms of the 
hands, first drawing it towards him and then pushing it from 
him, and patting the ends to bring it to a form similar to the 
mould into which it is to be introduced, (the mould having been 
previously sanded,) and presses it down with force, so as to fill 
up all the corners. The superfluous earth is now cut off by run- 
ning a steel tool like a large thick knife, called a plane, along the 
top of the mould, when the top of the brick is sanded, and a 
thin board, called a turning board, as wide as the mould, and three 
inches longer than it is, is laid over it, and the whole being in- 
verted, the mould may be raised carefully by the two hands, and 
the soft brick will be left on the turning-board, in which state it 
is taken away. Should any clay remain about the mould, it is 
now cleaned out and sanded, to prepare it for the next brick. It 
should here be observed, that the mould must be full half an inch 
or more longer, and a quarter inch wider and higher, than the 
brick intended to be produced, as all clay will sink thus much 
in drying, and sometimes more. 

482. In order to receive the bricks when moulded, a high and 
open piece of ground is provided called the floor, and this is 
formed into what are called hacks. The hacks are perfectly 
level projections of earth about two feet wide, and rising six 
or eight inches above the surface of the floor, and are fifty yards 
or more in length, for receiving the bricks to be dried, and they 
should run in a north and south direction, in order that both 
sides of the pile may receive its due proportion of sun-shine, and 
they must be about four feet apart to allow wheeling with a bar- 
row between them. The boy that receives the bricks from the 
34 



26Q ON BUILDING MATERIALS. 

moulder, holds them by the ends of the turning-board and places 
them on a barrow constructed for the purpose, with a high rais- 
ed stage of frame-work, that is level when the barrow is running, 
and holds twenty bricks. It must run upon planks to prevent 
concussion to the yet tender brick. He carries them to a hack 
and lays them regularly upon it, leaving the turning boards under 
them until the row is nearly filled, and this allows time for the 
bricks to dry and become a little hard on the surface, which they 
will do in half an hour in fine weather. Another who is in at- 
tendance at the hacks, takes them up and moves them to the next 
adjoining hack, previously covered with sand raked smooth, and 
in doing so places them on their edges by inclining the turning- 
board with one hand, and applying the other to the brick, while 
he slides away the boards to be returned in the empty barrow to 
the moulder. The soft bricks are thus disposed in an angular 
manner like a worm-fence, but in no case more than two inches 
asunder in the widest part, and not touching anywhere. The 
row or hack being finished, the bricks are sanded on their tops, 
and if the hack is long, the bricks at the end first put down, 
will be dry enough to permit a second tier to be laid upon them, 
and so on until eight tiers or layers are so disposed, which is the 
greatest number that can be placed without danger of crushing 
or spoiling the shape of the lower bricks, and this number should 
not be attempted unless the hacks are long, and the weather fine 
and dry. The object of placing the bricks in this open manner, 
is to permit the air to blow through and dry them as effectually 
as possible, but they must not dry too rapidly, as that will cause 
them to crack. Should the sun be too powerful, the hack will 
require shelter, which is obtained by constructing a number of 
light frames of a kind of basket work of twigs and straw inter- 
woven. They are six feet long, as high as the hacks, and made 
as light as possible. These straw hurdles are so useful, no brick- 
maker should be without them; they afTord shelter against both 
sun, rain, and frost, (which are the greatest enemies of the brick- 
maker in this stage of the business,) or they are set up in angu- 
lar positions to catch and direct the wind into the hacks, if the 
bricks dry too slowly. Should violent rains come on which 
might destroy all the work, the top of the hacks must be thatch- 
ed, by placing long wheat or rye straw transversely across their 
tops, keeping it from blowing away by planks laid lengthwise 
on them. The hacks are raised above the natural soil, for the 
purpose of keeping the lower tier of bricks out of the wet, should 
rain occur. 

483. In about a week the bricks will be sufficiently dry for 
turning, which is done by moving them from the hack on which 



ON BUILDING MATERIALS. 267 

they were first dried, to the adjacent one left empty to receive 
them. They are now disposed as before upon their edges, but 
are put parallel to each other, about one inch apart, and the side 
that was before downwards is turned upwards. In the second 
tier or course, each brick is placed over the opening between the 
two below, and so of all courses that succeed until the eight tiers 
are again completed. In this manner they still expose consider- 
able surface to the air, and as the bricks have now become tolera- 
bly dry, and do not require sun, the last drying hacks are some- 
times covered for their whole extent with a slight thatched roof, 
to protect them from rain; or if the kiln is not ready, they are 
sometimes moved into a building for safety. The hacks some- 
times require turning three or four times before the bricks are 
sufficiently dry for the kiln, and the drying usually takes from 
three to five weeks, depending on the state of the weather. 

Bricks are always made by piece work near London, where a 
skilful moulder, having all things in good order around him, 
will mould and hack from five to seven thousand in a day of 
fourteen hours work, or about five hundred bricks per hour; but 
to accomplish this he will require six hands to wait on him, all 
of which are children. They supply him with the tempered 
clay and sand, and water to dip his tools into, remove the bricks 
as fast as they are moulded, and return the turning boards. 

484. When small quanties of brick are required in a country 
where they cannot be obtained, or for particular jobs, the clay 
may be tempered and mixed by placing it on a hard bottom, 
and working it by a shovel or spade with water, and trampling 
it in the manner already described for puddling (391,) instead of 
waiting for a frost to break it down. In this case more water 
must be added than is fit for tempering brick earth, but it can be 
got rid of afterwards by draining it away, or exposing the earth 
to dry; when the moulding and drying must be conducted as 
above described, but on a smaller scale. 

485. In the vicinity of London, where the demand for bricks 
is enormously great, the large brickmakers adopt a different 
method to that above described for tempering and preparing 
their clay, but there is no variation in the manner of moulding 
and drying upon the hacks. The clay is dug in autumn and 
frosted as usual; but instead of being piled in ridges or small 
heaps, the whole is wheeled into one immense pile, as frosting 
the interior is of less importance when machinery is used. At 
the breaking up of the frost the clay is carried in navigators' 
barrows to a mill called a pug-mill, v/here it is worked by horse 
power, and incorporated with the necessary quantity of sand, 
chalk, or other material, and water, which is often pumped up 



26S ON BUILDING MATERIALS. 

and delivered into the mill, by the same power, in such quantity 
as will reduce the whole earth to so thin a state that it is just 
capable of running from an opening made in the bottom of the 
mill for its discharge. It is received upon a wire sieve or 
strainer, that stops all stones or foreign ingredients, if their size 
would prove prejudicial to the bricks about to be made. Two 
capacious ponds or reservoirs, about three or four feet deep, are 
formed for receiving this diluted earth, and they are so placed 
in respect to the mill, that its produce can be discharged into 
either at pleasure, by means of wooden shoots or spouts. The 
pugged stuff is conducted into one reservoir until it is quite filled, 
when it is turned into the other; and while the second is filling, 
the earthy matter subsides in the first, leaving nothing but clear 
water at the surface, and this is carefully drawn off by withdraw- 
ing pegs, that are placed very close, one below the other, from 
holes in a thick plank let into the upper part of the reservoir. 
In this way the water is drained off and runs to waste, leaving a 
finely divided and most equable mud in the reservoir, which be- 
comes of such consistence by draining, that it can be taken up 
by shovels, put into barrrows, and be taken away. The dis- 
charge of the mill is then again turned into the first reservoir, 
which fills, while a similar draining and removal of the contents 
of the second is taking place. In this manner the clay is more 
minutely divided and broken up, or tempered, than could possi- 
bly be done by the former process of hand labour, and in its soft 
state, when first moved, is in excellent condition for receiving 
finely sifted breeze, or any thing else that may be necessary for 
improving the quality or colour of the brick. After this, all 
that is necessary for rendering the earth fit for the moulder, is a 
few days exposure to the air, to make it sufficiently dry for his 
use; and then the process proceeds exactly as before described, 
unless indeed a patent moulding machine should be employed, 
instead of a hand moulder, for forming the bricks, and then the 
compost is delivered to the machine, of which there are several 
varieties, said to produce more compact bricks than hand mould- 
ing, because greater pressure is exerted to compress the clay into 
the mould than can be exerted by a man working the whole day 
through. 

4S6. The form of the pug-mill^ and its connexion with a 
pumj) for supplying it with water, is shown at Fig. 118, Plate 
IV, It consists of a very strong kind of conical tub a, formed 
of oak staves of two inches in thickness, and bound together by 
strong iron hoops, like a barrel. Its dimensions must depend 
on the quantity of work to be performed, but it is usually four 
feet diameter at the bottom, and three feet six at the top, having 



ON BUILDING MATERIALS. 269 

a height of about six feet. It has no bottom, that being supplied 
by the level ground into which it is sunk a little, and the earth 
may be banked up round it to render it more steady. It should 
stand on a platform of clay or earth impervious to water, pre- 
pared for it. This barrel or external case is to hold the clay, and 
expose it to the action of the revolving rakes or agitators, seen 
in J^ig. 119, (which is a sectional and internal view of a similar 
mill on a larger scale,) in which 5 is a vertical square iron shaft, 
the bottom of which ends in a pivot that works in the cast-iron 
box or step c, driven into the ground, or what is better, attached 
to a horizontal beam of wood let into the ground; this shaft 
carries several horizontal arms of wood or iron d d, and others in 
a cross or right angled direction as at e e, all of which are equip- 
ped with a number of iron teeth like those of a harrow, and about 
the same length and size. These teeth all incline or point forwards, 
or in the direction the shaft is moving in, in order that they may 
have a tendency to raise or lift up the clay, which by its weight 
falls through them towards the bottom of the tub; and thus by 
the two actions, the lumps are broken and mixed with the water, 
and the clay is more effectuall}'" and speedily broken, and reduced 
to a uniform mass, than it could be by hand labour. An inclin- 
ing flat blade or scraper, the length of which is very nearly equal 
to the radius of the bottom of the tub, is fixed at f, for the pur- 
pose of scraping the bottom, and keeping it free from adhesion 
of the clay, which might otherwise block up the orifice through 
which the pugged clay is to be discharged. Fig. 118 shows the 
arrangement for fixing and giving motion to the mill. A long 
beam of timber g is supported upon two posts firmly let into 
the ground, and properly braced, to make the whole frame stiff 
and strong. The upper end of the upright raking shaft b is con- 
fined in the cast-iron box or bearing A, so that it can revolve 
freely. A wooden arm i is keyed on to the upright shaft, close 
above the tub, and to the yoke at the opposite end of this the 
horse is attached, and walks round the tub in a track that should 
not exceed sixteen feet in diameter, or the motion will be too 
slow. If the mill is large, and the clay stijQf, it may be necessary 
to have a double arm z, and to employ two horses on opposite 
sides, but this will not be required if the mill has a good supply 
of water. The water is often pumped into the mill by a hand- 
pump fixed in a reservoir that is kept full, or may be supplied 
by the horse's motion, if a crank k is fixed on the top of the ver- 
tical shaft, and connected by a rod rn to the bent lever /, which 
works the pump jo, the water of which is conveyed by the shoot 
or trough 7^ n into the mill. This trough should have a hole in 
its bottom to be stopped with clay, in order that if the pump de- 



270 ON BUILDING MATERIALS. 

livers too much water, a part of it may be stopped and made to 
run to waste. Planks are laid from the heap of clay to the top 
of the frame-work g, and 5^ is a hopper by which the barrows 
of clay are discharged into the mill, in which it is retained until 
sufficiently worked; and this is regulated by the sliding door r, 
by the opening or partial closing of which, the pugged clay may 
be drawn ofif as slowly or rapidly as required. The contents are 
discharged into a short drain ,s, passing under the horse-track, and 
this delivers it into a box or hopper containing a wire-sieve for 
stopping stones, or any thing too large to be mixed with the 
b#ick soil. This sieve is placed at the end of the moveable shoot 
that conveys the stuff into one or other of the two reservoirs at 
pleasure, as before mentioned. 

487. All that now remains to be done, is the burning of the 
bricks, which is an operation of great nicety, because, if not burnt 
enough they will be soft and worthless, and, if over done, they 
vitrify, loose their shape, and often run together so as to be in- 
separable and useless. Accordingly, various methods have been 
adopted for producing the due degree of firing as it is called. In 
general, bricks are burnt, both in this country and in England, 
in a kind of building constructed for the purpose, and called a 
brick-kiln; but in London, the burning constantly takes place in 
the open air, the bricks being made up into immense quad- 
rangular piles, consisting of from two to five hundred thousand 
bricks in each. The built kiln is thought by many to produce 
the best bricks, or at all events, a larger proportion of good 
bricks out of any given quantity, and must certainly consume 
less fuel, but as they are never adopted in the immense brick 
manufactories of London, where no pains or expense for con- 
ducting the concerns in the best and most advantageous manner 
is spared, this is evidence that there must be some objections to 
them, for if they possessed real advantages, there can be no 
doubt but they would be adopted. 

488. A brick-kiln, as usually constructed, is formed of bricks 
built into a square form like a house, with very thick side walls, 
and a wide door- way at each end, for taking in and carrying out 
the bricks; but these doors are built up with soft bricks laid in 
clay, while the kiln is burning, and a temporary roofing of any 
light material is generally placed over the kiln to protect the raw 
bricks from rain while setting, and so made that it may be re- 
moved after the kiln is fired. The English kilns are generally 
thirteen feet long, ten feet wide, and twelve feet high, which 
size contains and burns 20,000 bricks at once. Wood is the 
usual fuel used in these kilns, and they are frequently built with 
partitions, for containing the fuel and for supporting the bricks, 



ON BUILDING MATERIALS. 271 

in the form of arches, as will be presently described. A brick- 
kiln has no flue or chimney, as its chief purpose is to direct the 
heat of the fire through the body of bricks piled above it. To 
effect this they must be placed in a particular form with great 
care, and this operation is called setting the kiln, and is perform- 
ed by one or two men who understand the business, and to whom 
the raw bricks are delivered in barrows. The form of the set- 
ting is pretty nearly the same in the country kilns, or London 
clamps, except that in the latter the arches are much smaller, be- 
cause wood is only used for kindling and not for burning. 

The bottom of the kiln is laid in regular rows, of two or three 
bricks wide, with an interval of two bricks between each, and 
these rows are so many walls extending lengthwise of the kiln, 
and running quite through it; they are built at least six or eight 
courses high, so as to give the kiln the appearance shown in Fig. 
120, which is an end view of it. And this is permanent work, 
or work that remains in the kilns that have fire-places built in 
their floors, or has to be formed every time the kiln is set, when 
it has a flat bottom. The intervals between the walls are laid first 
with shavings, or light and dry brushwood, or any thing that will 
kindle easily, then with larger brushwood cut into short lengths, 
that it may pack in a compact manner; and, lastly, with logs of 
split hickory, or strong burning wood. This done, the over- 
spanning or formation of the arches is commenced; for this pur- 
pose every course of bricks is made to extend an inch and a half 
beyond the course immediately below it, for five courses in height, 
taking care to skintle well behind, that is, to back up, or fill up 
with bricks against the over-spanners. An equal number of 
courses, on the opposite side of the arch, is then set as before, and 
thus the arch is formed, which is called rounding, and is a nice 
and important operation, for if the arch fails or falls in, the fire 
may be extinguished, or many of the bricks above the arch may 
be broken. The intermediate spaces between the arches are now 
filled up, so as to bring the whole surface to a level, and then the 
setting of the kiln proceeds with regularity until it obtains its full 
height. In setting the kiln, not only in its body, but in the 
arches also, the ends of the bricks touch each other, but narrow 
spaces must be left between the sides of every brick for the fire 
to play through, and this is done by placing the bricks on their 
edges, and following what is called the rule of three upon three, 
by brickmakers, reversing the direction of each course as shown 
at Fig. 121. The kihi being filled, the top course is laid with 
flat bricks, so disposed, that one brick covers part of three others, 
which process is called platting. 

489. The kilns of Philadelphia are constructed and managed 



273 ON BUILDING MATERIALS. 

in a manner very nearly according with the above description of 
the country kilns of England, but they are larger, having an 
average width of twenty-eight feet in the clear, and are higher; 
but the bricks are not laid more than thirty-five or thirty-six 
courses. There are seven arches or firing holes in the end, each 
two feet high by sixteen inches wide, and the distance between 
each arch is three bricks. Such a kiln holds 140,000 bricks, and 
consumes from forty to fifty cords of wood for burning them. 

490. The kiln being built, or finished, the firing succeeds, and 
this is the most delicate operation, and one that requires practice. 
The fuel is kindled under the arches, but requires close watch- 
ing and attendance, for being in a large body, it would burn vio- 
lently and produce so sudden a heat as would crack and spoil the 
lowest bricks. To check the burning, the arch holes or mouths 
are closed with dry bricks, or even smeared with wet clay, in 
order to prevent the entrance of air, and rapid combustion that 
would ensue. The fire must be made to smother rather than 
burn, in order that by its gentle heat it may evaporate away the 
humidity that remains in the bricks, and produce drying rather 
than burning. The slow fire requires to be kept up about three 
days and three nights, by occasionally opening the vents, to sup- 
ply air and additional fuel, and closing or partially closing them, 
until the fire gets up, as the workmen call it, that is to say, until 
it has found its way through all the chinks and openings between 
the bricks, and begins to heat those at the top of the kiln. To 
ascertain the progress of the fire, the top of the kiln must be 
watched, and as soon as the smoke changes colour from a light 
to a dark hue, the drying is complete, and the fire may be urged. 
The first, or white smoke, called water-smoke, is, in fact, little 
else but the steam of the water while evaporating, and when that is 
gone, the real smoke of the fuel succeeds, and now the vents may 
be opened to admit full draught, and a strong fire kept up for 
from forty-eight to sixty hours; but the heat must not be white 
or so strong as to melt or vitrify the bricks, and whenever it ap- 
pears to be increasing too rapidly, the vents must be partially 
closed. By this time the kiln, if it contains thirty-five courses, 
will be found to have sunk about nine inches: but the stronger 
the clay the more it will shrink, and it is by this sinking that 
the workman knows when the kiln is sufficiently burnt. The 
experience of burning a few kilns will show how much the clay 
of that particular place yields to the firing. When it is thus as- 
certained that the kiln is done, the vent-holes, and all other chinks 
through which air can enter, are carefully stopped with bricks 
and clay, and in this state it remains until the bricks are cold 



QK BUILDING MATERIALS. 273 

enough to be taken down, when they are distributed for use. 

491. From the nature of the above process it will be evident 
that bricks of very different qualities will be found in the same 
kiln; for as the fire is all applied below, the lower bricks in its 
immediate vicinity will be burnt to great hardness, or, perhaps, 
vitrified; those in the middle will be well burnt; and those at the 
top, which are not only most distant from the fire, but exposed to 
the open air, will be merely baked, and not burnt at all; conse- 
quently, if they can be used, they must be reserved for inside 
work, that is not exposed to weather, or they will soon fail and 
crumble to pieces. 

492. In the London method of open clamp burning, without 
any kiln, the piling and disposition of the bricks is the same as 
above described, except that the bottom arches are much smaller, 
as they are only intended to contain brushwood to produce the 
first kindling, and not for the future supply of fuel. No fuel is 
used except the breeze cinders and small coal before described, 
and this is distributed by means of a sieve, with wires about half 
an inch apart, over every course as it is laid near the bottom, and 
over every alternate course, or every third course higher up in 
the kiln. The first layers of this fuel are from an inch to an 
inch and a half in thickness; but they diminish as they ascend, 
because the action of the heat is to ascend, consequently there is 
not the same necessity for fuel in the upper, as in the lower part 
of the kiln. The brushwood in the bottom ignites the lower 
stratum of fuel, and from the nature of its distribution, the ver- 
tical as well as horizontal joints will be filled with it, and thus 
the fire gradually spreads itself upwards, and the whole clamp 
is nothing but a mass of bricks and burning fuel. The heat is 
therefore much more generally distributed throughout the whole 
mass, and in order to confine it, the entire outside of the clamp 
is thickly plastered with wet clay and sand, the bottom holes 
being opened or shut as occasion may require for regulating the 
draught of air. 

493. Notwithstanding the heat is much more equably distri- 
buted throughout this form of kiln, yet the outside bricks all 
around receive very little advantage from the fire, and are never 
burnt; but being on the outside they are easily removed, and are 
reserved for the outside casing of the next clamp that may be 
built; and being then turned with their unbaked sides inwards, 
some of them become available. On taking down the clamp, 
the bricks are assorted, in London, into three separate parcels or 
varieties, according to their perfection and goodness. Those 
that are burnt very hard but have not lost their figure or shape, 

35 



274 ON BUILDING MATERIALS. 

are called malms, or malm -facings, or malm-paviors, and are 
used for facing good work; or for paving, for which their hard- 
ness makes them peculiarly suitable. The main body of the 
clamp produces well burnt and regularly formed bricks called 
stocks, with which the generality of houses are built; and such 
as are imperfectly burnt, and are soft, are called place bricks. 
These last are used for inside partitions, backing walls that are 
to be plastered upon, and other work that is neither exposed to 
the eye or the weather. These several varieties of brick have 
each a separate price, the best being worth almost twice as much 
as the worst. If the fire has not been carefully attended to, and 
has been permitted to get too violent, a few of the lower bricks 
will become distorted by partial fusion, and may fuse and adhere 
together, when they are called clinkers, and are useless for build- 
ing purposes, but form an excellent road material. In this coun- 
try the names of bricks are different, but derived from the same 
source, being called hard burnt or arch bricks, body bricks, and 
soft or salmon bricks; though this last name is generally altered 
by workmen into sammy. The goodness of a brick is derived 
from its regular shape and appearance, its tenacity and hardness, 
its sound, and by its not absorbing water, or being affected by 
frost. The tenacity and hardness are judged of by striking one 
brick against another, or letting them fall upon stone pavement. 
Good bricks should have a sound approaching to that of a metal 
vv'hen so treated, and they ought to ring, and bear a very hard 
blow with the edge of the trowel, before they divide. If they 
readily break with a blow, or crumble to dust by a fall, such 
bricks are of the soft or sammy kind, and are unfit for introduc- 
tion into a heavy wall, particularly on the outside of it, as they 
will be sure to be attacked by frost, and crumble to pieces. The 
absorbency of bricks is judged of by weighing them in the 
dry state, and then soaking them in water for an hour, and 
weighing them again. Those bricks that take up the greatest 
quantity of water, are the least fit for use, when they are to be 
exposed to its action. The average weight of a sound and dry 
London stock brick, is four pounds fifteen ounces avoirdupois. 

494. Independent of the above, two other kinds of brick are 
made, called cutters or rubbers, and fire-bricks. Cutters or 
rubbers are very common in London, but not so generally used 
in this country. They are made of the best and most select 
materials, passed through a much finer sieve or strainer than the 
other bricks, and the whole manufacture is conducted with pecu- 
liar care, on which account they are expensive. They derive 
their name from their being so perfectly homogeneous, and free 
from stones or hard parts, that they may be cut with a saw, or 



ON BUILDING MATERIALS. 275 

chopped to any form, and then rubbed on a rubbing-stone until 
they obtain a perfectly flat surface. They are only used for or- 
namental puposes, such as constructing gauged or rubbed arches 
over doors or windows, niche heads, and the like. 

495. Fire-bricks are used for lining the insides of furnaces of 
all kinds, in which the heat may be so great as to fuse and vitrify 
bricks of ordinary materials. They are also used for that part of 
the setting of steam-engine boilers that is most exposed to the 
fire, and for lining the insides of fire-places intended for burning 
anthracite coal. Until the last few years, these bricks were im- 
ported from England, where two varieties of them are made, 
called Stourbridge and Windsor fire-bricks, both excellent, but 
of very different qualities, and they both derive their value from 
the peculiar local earth of which they are formed. The Stour- 
bridge brick is always larger than other bricks, of a pale yellow 
or red colour, and when well burnt so hard that it will give 
fire with steel, and has no absorbent power. When broken, it 
may be seen that this brick consists chiefly of the same brick 
previously burnt, and reduced to coarse powder, and then made 
over again with an additional quantity of the same fire-clay. 
The Windsor brick, on the contrary, is made below the usual 
size, and is so soft and tender, that it can scarcely be handled 
without breaking, and when broken its whole substance is dis- 
covered to be nothing but sand, cemented and held together by 
a very minute quantity of argillaceous earth. This brick is of 
a deep, but bright red colour throughout, and is so soft that it 
may be cut to any required form by a common sau^ or knife, 
notwithstanding which, it withstands a higher heat than the 
former kind, and becomes very hard and durable after it has been 
exposed to such heat. On this account it is constantly used for 
forming the arch over wind or reverberating furnaces for melting 
iron. A similar brick is made at Cheam in Surrey, and as they 
are all stamped with PP, they are known under the name of 
PP or nonsuch bricks. Each of the above kinds fetch fifty 
dollars a thousand in London. Within the last few vears, the 
Stourbridge brick has been most precisely imitated in this coun- 
try, as to size, colour, texture, and quality; the writer has tried 
these bricks against those of England, and finds them fully equal 
in goodness and power of resisting heat. They sell in Baltimore 
for something less than the English brick, which makes them 
much cheaper than those that are imported. He has never seen 
any attempt to imitate the nonsuch brick, but has no doubt they 
might be made as well as the others. The hard brick should be 
used in all furnaces subject to blows or concussions, as when large 
logs of wood are thrown in, or the fire has to be raked with large 



276 ON BUILDING MATERIALS. 

iron pokers; but for domes, or places not likely to be disturbed, 
and where the heat is very great, the soft bricks will be found 
preferable. Large blocks, called lumps, are made of the Stour- 
bridge material, and are very useful in the construction of many 
furnaces. Fire-bricks are often made wedge-formed for building 
arches, and in segments of circles, for building round furnaces or 
flues. 

496. Common brick earth is frequently formed into what are 
called drain bricks; they are made large enough to admit of 
having a semi-circular cavity of about three inches diameter sunk 
into one of their sides, so that two of them inverted, one over 
the other, form a three inch tube, with a square outside. 

497. Tiles are a kind of thin brick, made exclusively for 
covering buildings, and they are so little known or used in the 
United States, that it appears hardly necessary to mention them, 
except that our account of bricks would be incomplete without a 
notice of them. In London, almost every ordinary house is 
covered with tiles, as they, with slates, form the only roof cover- 
ing, except in some few instances where copper or sheet lead are 
used for flat roofs. Slating is only adopted in the more elegant 
and expensive buildings, as forming a much lighter covering, 
and one more elegant in its appearance than tiles. Indeed the 
only objection to tiles is their weight, in consequence of which 
they require stronger timbering in the roof. But still they pos- 
sess advantages over both the other materials. Metal is objec- 
tionable on account of its ready transmission of heat and cold to 
the building below, the noise that rain occasions when falling upon 
it, and the liability to expansion and contraction, which causes 
it to crack and admit water. Slates on the other hand from being 
very thin and light, are frequently affected, and even lifted by 
high winds; are so brittle that they are easily broken by passing 
over them, and they transmit heat and cold very readily, while 
tiles are too heavy to be affected, are bad conductors of heat, are 
strong, and may be said to be imperishable; for the older tiles 
are, the better they are considered, because they lose their ab- 
sorbency by age, and while they are cheaper than the other 
coverings, they are perfectly weather-tight, resist fire, and seldom 
need repair. 

498. Tile-making is quite a distinct business from brick- 
making, and they are never carried on by the same persons. 
Tiles require a stronger clay than could be used for bricks, a 
smaller proportion of sand, and no breeze. The clay is some- 
times worked by the pug-mill, but generally by hand labour, as 
a much smaller quantity of it is required than for bricks; but 
tiles are moulded in very nearly the same manner, are dried in 



ON BUILDING MATERIALS. 277 

the open air, and then burnt in very large and high conical brick 
buildings called tile-kilns, in which they are treated in a manner 
very similar to pottery-ware. 

490. Tiles are confined to three varieties or shapes, called, 
plain tiles, pan-tiles, and ridge-tiles, and each variety is always 
made of the same size, so that whether bought at one establish- 
ment or another, they fit and work together. The plain or flat 
tile is the kind most approved and used, as affording a neat look- 
ing and perfectly water-tight roof, and with this tile most of the 
houses in England are covered. Plain tiles are ten and a half 
inches long, six and a quarter wide, and five-eighths of an inch 
thick, and each tile weighs two pounds five ounces. There are 
two small holes made near the end of each tile to receive wooden 
pegs, by which the tile hangs on to strong laths nailed from one 
rafter to another, and these tiles are often laid dry, or without 
mortar, overlapping each other just like shingles. If bedded, 
or laid in a very small quantity of mortar, plain tiling not only 
resists rain, but the drifting of snow likewise; and as tiles are 
very bad conductors of heat, so a bedded plain tile roof protects 
the building over which it is placed from the vicissitudes of at- 
mospheric temperature in a remarkable degree. 

500. Ridge-tiles are a plain tile of larger dimensions, bent at 
the time of making, into a curved form, for the purpose of being 
placed over the ridges, or angular edges, where the two sides of 
tiling meet, to make a finish and exclude water. They are 
always set in mortar, and in addition, are held down by a pecu- 
liar thin nail with a large head, made for the purpose, and driven 
between each tile into the timber ridge piece, so that the head of 
one nail confines two tiles, and prevents their being blown off, 
or otherwise displaced, even after the mortar decays. 

501. Pan-tiles are a tile so curved that by one edge of the tile 
being bent down, and the other turned up, while a hollow is left 
between them, one tile fits under and over the adjoining one; and 
thus a water tight roof is produced by only one single layer of 
tiling, in a manner that will be understood by referring to Fig. 
122, Plate IV., which shows the disposition of a few tiles laid 
on a roof. Each tile has a projection formed on the under side 
of its top part, by which they are hung upon laths or slats of 
wood, nailed at proper distances to receive them, and to permit 
the lower end of the highest tile to overlap the upper end of that 
immediately beneath it, as will be seen in the section of this 
tiling, shown by Fig. 123. Pan-tiles are thirteen and a half 
inches long; cover nine inches of width; and, consequently, are 
about twelve inches wide before they are curved, and half an 
inch thick, and each tile weighs about four pounds eleven ounces. 



278 ON BUILDING MATERIALS. 

They are much used for shed or temporary roofs, as from the 
ease with which they are laid on, a large space may be covered 
in a very short time, and they are the cheapest and lightest kind 
of tile covering. They keep out rain very effectually, but ex- 
pose openings through which air and drifting snow can pass; but 
they are much esteemed on this account for covering founderies, 
blacksmiths' shops, and chemical establishments, where much 
smoke or bad fumes are produced, as they pass off readily between 
the tiles, and the rooms covered with them are kept well ven- 
tilated, and supplied with fresh air; but if pan-tiles are laid in 
mortar and pointed, they make a perfectly good and sound roof, 
and many dwellings are covered by them so laid, although their 
general use is confined to stables, manufactories, farming build- 
ings, and houses of small dimensions. 

502. The tile-makers also prepare excellent hard paving tiles, 
of twelve and ten inches square; the first, inch and a half thick, 
and weighing twelve and a quarter pounds each, and the lat- 
ter, one inch thick, and weighing eight and a half pounds each. 
When bedded in sand and mortar they make an excellent paving 
for manufactories, kitchens, dairys, and other buildings, and are 
very level, durable, and cleanly. 

Section II. — Of Lime, Mortar , and Cements. 

503. The stones and bricks, spoken of in the last section, 
would be of little avail in the building art, was it not for some 
material by which they could be united together, so as to convert 
the small separate pieces of material into one united mass; and 
this is effected by the intervention of mortar or cement. The 
general character of mortar and its use are well known; and ce- 
ment, among builders, is a name given to such kind of mortar as 
is capable of setting, or becoming hard, under water, a property 
that common mortar does not possess. 

504. Common mortar is composed of quicklime and sand duly 
prepared, and mixed with w^ater until it becomes a paste of pro- 
per consistence, to be applied by that well known instrument 
the trowel. It is applied by making a sufficiently thick layer, 
or bed of it, and then placing the stone upon it with artificial 
pressure, if its weight is not sufficient to produce the necessary 
setting or compression; when the quantity of superfluous mortar 
that squeezes or oozes out of the joint, is removed by the trowel 
for future use, and the outside of the joint being passed over and 
made smooth by the point of that instrument, the stone is left for 
the mortar to set or get hard. There is a great variety in the 
nature of quicklime, as well of the materials of which it is form- 



ON BUILDING MATERIALS. 279 

ed, and some art in preparing and using it, therefore some ob- 
servations on these heads will be necessary. 

505. Limestone is one of the most abundant products of the 
earth, existing in all countries to a greater or less extent, and 
often in mountain masses. Lime is, however, never pure or un- 
mixed, unless in rare mineral specimens, but is always mixed 
with carbonic acid gas, sulphuric acid, or some of the strong 
mineral acids. The carbonate of lime is alone fit for the purpose 
of making mortar, and this, as before observed, assumes a great 
variety of forms, possessing little or no external similarity. 
Thus, all the marbles are carbonate of lime. Carbonate of lime is 
sometimes beautifully crystallized in detached crystals, or is 
found in masses evidently crystalline. Some of the mountain 
limestones possess this character, while others are earthy and 
even lamellar. The hard masses of dark grey limestone, used for 
rubble work in building, are often of this character. Chalk, 
which forms high clifis, and even mountains, in the southern 
parts of England, is entirely carbonate of lime, and nearly all the 
lime that is consumed in London is nothing more than burnt 
chalk. Lime also exists in animal formations, for the shells of 
oysters and other fish, consist almost exclusively of carbonate of 
lime, which is also the case with many of the madrepores and 
corallines, of animal formation, found in the sea. 

506. All the carbonates of lime efiervesce when touched, or 
brought into contact with the strong chemical acids, such as the 
sulphuric and muriatic, or hydrochloric acids, and are soluble in 
them, if in excess, and this is one of the tests by which lime is 
known. They are all very nearly, if not quite, insoluble in pure 
water, and they part with their carbonic acid on being exposed to 
a red heat. This, therefore, is the reason why limestones are 
burnt or heated. The heat dissipates or drives off the carbonic 
acid, and a large portion of the water that was previously com- 
bined with the limestone, and after this process, whatever may 
have been its previous colour, it is rendered quite white, or of a 
light brown colour, and is now called quick, or caustic lime. 
The term, caustic, is applied to it from its property of apparently 
burning things, for it has so very strong a disposition to unite 
again with carbonic acid and humidity, that it will even destroy 
the flesh to get at these ingredients; and if water is added, to a 
certain extent, to quicklime it will disappear, and become solidi- 
fied in the stone, which bursts to pieces, and afterwards falls into 
a very fine powder; great heat being given out while the combi- 
nation is taking place. The lime is then said to be slaked. 

507. Lime in its caustic state is slightly soluble in water, con- 
verting it into what is called lime-water; and if carbonic acid is 



280 ON BUILDING MATERIALS. 

thrown into this water, it will combine with the lime, and by ren- 
dering it insoluble again, will cause it to appear; in doing which 
it first makes the water turbid or milky in appearance, and the 
lime is soon precipitated to the bottom in its former state of car- 
bonate of lime. This seems to point out the use and operation 
of mortar. If raw or crude limestone in its natural state should 
be powdered and mixed with water, it has no greater disposition 
to form a paste or adhesive mass, than sand would have; and 
when it becomes dry by the evaporation of the water, the lime- 
stone will again be found in the state of powder, without any 
union or tendency to form a solid or compact mass. But if that 
same limestone is burnt, so as to become deprived of its carbonic 
acid and natural humidity, on being mixed with water, a combi- 
nation will take place, a part of the lime will be dissolved in it, 
and a paste will be formed which gradually imbibes carbonic 
acid from the surrounding air, by which it is rendered insoluble, 
and the water now gives back the lime it had previously dis- 
solved, which probably shoots into a kind of crystallized or 
rather interlaced formation, by which not only one particle of 
lime is held to another, but adhesion is produced to the stone, 
brick, or other substance, with which the lime may be in con- 
tact. 

508. The lime in setting or hardening, becomes re-converted 
into a kind of stone, and it is a singular fact, that the hardness 
of this artificial stone, bears a relation to the hardness of the 
original stone before it was burnt, thus giving a decided charac- 
ter of superiority to one kind of limestone over another, for the 
purpose of burning lime for mortar. London and Philadelphia 
offer a striking contrast in this respect. Nearly all the lime con- 
sumed in London, is produced from burning chalk, and is there- 
fore called chalk-lime. Chalk is of two kinds, stone chalk, and 
soft chalk; stone chalk is hard and compact, contains hard and 
gritty particles, and will rather scratch than mark upon a board, 
if used for the purpose of marking or writing. Soft chalk, on 
the contrary, is equable and smooth in its texture, and marks or 
writes freely; but it exists only in small quantities compared 
with the other, and is wholly unfit for making building lime, 
although it makes the best for agricultural purposes. Of course 
the lime-burner selects the hardest chalk he can obtain, and the 
mortar made from it is tenacious and durable.; but still after it 
has been used in buildings even for a year or two, no difficulty 
will arise in driving a nail into the joint between two bricks, 
and the mortar is easily raked out of the joints for pointing. 
But if the same trial is made upon the lime of Philadelphia 
burnt from marble, or the dark-blue limestone, which are alone 



ON BUILDING MATERIALS. 281 

used, the nail would inevitabl}^ be bent, and would be unable to 
penetrate the joint, even though it might not be more than six 
months old, the mortar being quite as hard as the brick. The 
excellence of the lime and bricks in this city, permits much 
thinner walls to be erected with confidence than could be done 
in London, where the mortar is of inferior quality, and where 
stone-lime is only used in buildings intended for great duration, 
on account of the additional expense of its transportation from 
distant places, rendering its price higher than the lime generally 
used. 

509. Limestone and chalk are burnt near London, and indeed 
wherever coal is abundant, by coal in preference to wood fuel; 
the coal being broken into very small pieces or almost to powder. 
As coal works cannot be conducted without producing a large 
quantity of this dust coal, it is reserved, and furnished to the 
lime-burners at a lower price than coal in large lumps. And 
many of the London coal dealers screen their coal, so as to sup- 
ply private families with large coal, at a little advance of price, 
which enables them to sell the small coal at an equivalent reduc- 
tion. 

510. A. lime-kiln as usually constructed, is placed, if possible, 
in the side of a natural hill to avoid the expense of brick- 
work or masonry in its construction; and as the lime is generally 
of chalk, it is easily formed by an excavation into a cliff or hill 
of that material. Indeed lime-kilns should always be built in 
the immediate vicinity of the stone to be burnt, to save its trans- 
portation, and if they cannot be formed in the natural soil, they 
must be wholly built. The kiln itself is an inverted cone exca- 
vated out of the soil, or formed in the brick-work or masonry, 
and must be lined with fire-bricks, or the hardest bricks that can 
be procured. Its form, as shown at Fig. 124, the cone « a is 
usually from twelve to fifteen feet in diameter at its top or largest 
end, and diminishes down to about three feet in diameter at 6, 
which is the draught-hole or ash-pit; and this opens by an arch- 
way to the front of the kiln, and should be high enough, near the 
front, for a man to stand upright to work in it. The cone should 
be from twelve to fifteen feet deep from its top to the base. Two 
strong iron bars, called bearing-bars, seen in section at c c, are 
fixed in the brick-work to bear or support the fire-bars that lie 
upon them, at about an inch asunder. These fire-bars are of 
wrought iron, about an inch and a half square, and more than 
two feet longer than the opening they have to cover, so that their 
ends d, project into the arch. The bars being properly arranged, 
a large fire of brushwood is made upon them, and coals are thrown 
upon it by baskets, from the circular platform e e, formed round 

36 



282 ON BUILDING MATERIALS. 

the top of the kiln. When the fire is properly ignited, a layer 
of chalk or limestone, broken into pieces, is in like manner 
thrown upon it, until the layer is about nine inches thick. Some- 
time afterwards a layer of coal is deposited in the same manner, 
and if the mass appears to burn well, the whole kiln may be 
filled with alternate layers of broken stone and coals, in a propor- 
tion that must be determined by trial upon the stone that is burn- 
ing, as some kinds take more fuel than others, but chalk will burn 
if the layers are in the proportion of ten to one. This is deter- 
mined by the baskets from which the materials are thrown into 
the kiln; they hold a bushel, and ten bushels of chalk require 
about one bushel of coal. When once the kiln is set properly to 
work, the fire requires no re-kindling, but its operation may be 
continued for months together, by merely supplying fresh mate- 
rials to the top of the kiln in the same proportion as the lime is 
drawn away from the bottom. The kiln is usually drawn every 
twenty-four hours, by taking out, or pushing to one side, one or 
two of the fire-bars d, when a quantity of the bottom or fully 
burnt lime falls down into the ash-hole b. If the lime does not 
fall fast enough, it is agitated by a bar of iron with its end turn- 
ed up about a foot. This is introduced up the hole between the 
bars, and the lime is easily got down. It is then drawn to the 
front of the arch by an iron hoe, and when cold, is ready for 
measuring and carting away. The workman judges from his 
experience how much lime he may draw at once, and if pieces 
fall that are not sufficiently burnt, they are returned to the top 
of the kiln again; but this seldom happens, because an ex- 
perienced kiln man will cease drawing before such pieces appear. 
The drawing having closed, the fire-bars are re-instated in their 
proper places, and the kiln is not touched again until the follow- 
ing day. 

It might be supposed that rain falling on a kiln of this descrip- 
tion, would be detrimental to the burning of the lime, and that 
a roof would be necessary for its protection. The heat is how- 
ever so great, that any rain water is evaporated without sinking 
into the kiln; and in dry weather the top of it is sometimes 
watered, as the presence of moist vapour in the upper part of the 
kiln is thought to assist in the escape of the carbonic acid gas. 
Some of the best modern lime-kilns have been built in the form 
of two truncated cones applied base to base, so as to contract the 
upper opening, and reflect the heat downwards, which no doubt 
must produce an economy of fuel, and this form ought to be 
constantly adopted in all kilns where the lime has to be burnt 
by wood; because this fuel will not admit of mixture with the 
body of the limestone, and must be apj^lied wholly from below. 



ON BUILDING MATERIALS. 283 

The upper part of tlie kiln is therefore deficient in heat, and any 
form that will augment or economise it, is advantageous. In 
lime-kilns for using wood, a fire-brick arch forming a dome or 
kind of oven, is built over the fire-place, and pierced with holes 
large enough to let the heat rise up, but not to permit the lime 
to fall through them, and the largest pieces of limestone are put 
into the bottom of the kiln, to insure large interstices for the 
flame to play through. The lime is withdrawn when burnt, by 
an arched door in the side, made independent of the firing oven, 
and this door must be bricked up while the lime is burning. 

511. As the fuel for burning lime, and the trouble and labour 
attending the operation, render it much more expensive than the 
raw materials that nature affords; and as burnt lime, however 
hard it may become, is more liable to decay by time than bricks 
or natural stones, and lime undergoes considerable shrinking as 
it dries, so mortar is never made of lime alone, but of lime and 
sand; and the goodness and durability of the mortar depends 
much on the quality of the sand used. Pure siliceous or flinty 
sand is imperishable by time, and is, therefore, the most suitable 
for the purpose; and as this consists of grounded grains like peb- 
bles, or of such as are sharp and angular, and experience seems to 
prove that the lime crystallizes around, or takes better hold of 
that which is sharp, so sand of that description is always pre- 
ferred. The great point to be attended to in selecting sand for 
mortar, is to get it as purely siliceous and free from materials 
that will wash away or decay, as possible. Good pure sand may 
be judged of by inspection, and by rubbing a quantity of it in a 
damp state between the hands; if it soils them by leaving dirt, 
clay, or any thing but sand upon the hands, it must contain clay 
or some soluble foreign matter. The best proof of its purity is 
to put a handful or two of the sand into a wash-hand basin, and 
having poured clear water upon it, to stir it about. If the sand 
is quite pure, it will scarcely soil the water in falling to the bot- 
tom; but if it contains much clay, vegetable matter, or other ma- 
terial, it will produce such a muddiness and discoloration of 
the water as will render the sand invisible, and as it produces 
more or less of this effect, it may be pronounced more or less 
pure. Mr. Smeaton, who in the course of a long and meritorious 
attention to his profession as an Engineer, found that when mor- 
tar, though otherwise of the best quality, was mixed with a small 
proportion of unburnt clay, it never acquired that hardness which 
it would have attained without it; and, consequently, sand of this 
description should be avoided. 

512. The best sand as to form, size, and purity for making- 
mortar is sea sand, such as is found on sea beaches; but there is 



284 ON BUILDING MATERIALS. 

one great objection to its use, which is the salt it contains, and 
from which it is very difficult to disengage it; and unless the sand 
is perfectly free from salt it crystallizes in dry w^eather, and 
deliquesces when it is damp, so as to spoil the appearance of any 
work done with it, and to keep the mortar in so damp a state as 
to prevent its setting well. Sea sand should, therefore, never be 
used until it has been thoroughly soaked and washed in several 
successive changes of fresh water, which is too troublesome to be 
adopted in works on a large scale. Fresh water river sand, or 
pit sand, that is, pure sand dug out of inland pits, are the kinds 
generally resorted to; and a preference is generally given to pit 
sand, on account of its being more pure and sharp than that ob- 
tained from rivers, the grains of which are, generally, rounded 
by attrition. Among the London builders sifted road sand is 
preferred to any other kind. This sand is procured from the mud, 
scraped after wet weather, from the much frequented high roads, 
and as these roads are all made and repaired with the hardest 
flint stones alone, the finest particles of this sand, even the dust, 
must be siliceous with very little admixture of any thing else. 

513. Much difference of opinion exists as to the quantity of 
sand to be mixed with lime for making the best mortar. Work- 
men like a large proportion of lime, because the mortar is more 
plastic, tenacious, and easy to work when that predominates; 
while, on the contrary, when the sand is in excess, the mortar 
will not hang together, and is said by the workmen to be too 
short. The facility of the workmen must not, however, be al- 
lowed to interfere with the stability of the work to be executed; 
and experience fully proves that brickwork, in which a super- 
abundance of lime has been used, though it may be strong for the 
few first years, is never so durable as when it exists in less 
quantity. 

Dr.Higgins, of England, whose name standshighly distinguished 
as one of the originators of the atomic theory in chemistry, was the 
first person who undertook a correct investigation of the mechani- 
cal and chemical action of mortar* on the true principles of science, 
and after many experiments and trials he gives the following as 
a result for the best mortar, viz: newly slaked stone quicklime, 
one bushel; fine siliceous sand, three bushels; and coarse sand of 
the same description, four bushels; making a proportion of seven 
parts of sand to one of lime. But he confesses this to be a very 
short mortar, and one with which it is difficult to work; "but," 
he adds, "that if a quarter of a bushel of bone ashes, or calcined 
bones in powder, is added to the above quantity, it will give it 

* Higgins on Calcareous Cements, 8vo., London. 



ON BUILDING MATERIALS. 2S5 

sufficient tenacity, and will render it much less likely to crack in 
drying.^^ In order to define what is meant by fine and coarse 
sand, which he says must be free from clay, salt, gypsum, or any 
thing less hard than quartz, he directs that the sand shall be sifted 
under the water of a running stream, in a sieve of wire-cloth, 
No. 16, that is, in which each hole or mesh is the sixteenth of 
an inch square. The sand that passes is collected, and sifted 
again through another sieve, in which the wires are thirty to the 
inch; all that will not pass through these sieves must be rejected, 
and the produce of the two sieves will give the fine and coarse 
sand above referred to. 

514. This mortar, the writer has no doubt, may be very good, 
but it would be very unpleasant and annoying to the workman. 
His opinion is that nature cannot be too closely copied in the 
formation of a mortar; and Portland stone may be considered as 
a natural mortar; for, as before observed, when examined even 
with a magnifier, it will be found to be nothinor but fine sand as;- 
glutinated together by a lime or calcareous cement, in too small 
a quantity to be perceived. It is, by geologists, ranked among 
the oolitic formations, but on examining the obvious oolite or 
Bath stone, in which the grains are much larger, the cementing 
material is distinctly visible, and the stone is much weaker. It 
may be imitated by wetting clear siliceous sand with strong lime 
water, that is so pellucid that no lime appears in it, yet after ex- 
posure for som.e time to the atmosphere, the grains will adhere, 
which shows how small a quantity of lime is necessary for the 
cementing process; but still a sufficient quantity must be allowed 
to produce facility and stability in the work. In the construction 
of a large quantity of brickwork, executed at the West Middlesex 
water-works, the only mortar used consisted of six measures of 
sand, (without the precaution of sifting and separating it as above,) 
to one measure of excellent lime, obtained from Merstham in 
Surry, about twenty miles from the works, that being the nearest 
good stone lime that can be obtained at London, and that work 
stood and looked remarkably well. It was the same materials, 
and the same proportion that had been previously used in the 
buildings of the London and West India docks. 

515. Chalk lime, and the weaker limes, will not bear any thing 
like this quantity of sand, and the general proportions of the 
London builders is one and a half hundred weight, or thirty- 
seven bushels of lime to two and a half loads, or fifty-five bushels 
of sand. The measures in both cases being struck or not heap- 
ed. The writer is, however, persuaded that this proportion of 
lime is too great. There is scarcely any mortar in which the 
lime has been well calcined, and the composition well beaten 



2SQ ON BUILDING MATERIALS. 

and mixed together, that will not take two parts of sand to one 
of lime; and it is worthy of remark that the more the mortar is 
beaten or chafed, the less proportion of lime will suffice. 

516. In the vicinity of the sea, where oysters, clams, and 
other shell-fish abound, while limestone may be scarce, the only 
lime used is that procured from the burning of shells. This is 
a very excellent lime, and is much used in the eastern parts of 
Virginia. It is of course called shell-lime. 

517. All quick-lime, from whatever substance it may be pro- 
duced, requires to be slaked before it can be made into mor- 
tar. The slaking is nothing more than pouring water in proper 
quantities upon the lime, previously spread upon the ground in 
a j^arcel of eight or ten inches thick. The water should be care- 
fully distributed over the whole surface of the heap, not in such 
quantity as to make the lime wet, or to run away from it, but 
merely to make it damp. If it was made wet, it would spoil 
the sifting or screening, which is the next process it has to un- 
dergo; and, as the sand has to be screened, as well as the lime, 
they are generally mixed together in their proper measured pro- 
portions before the screening begins. The sand being placed first 
on the ground, and hollowed into a kind of basin in which the 
lime is put, and the proper quantity of water having been pour- 
ed upon the lime, some of the sand is drawn over it by a hoe, 
and the parcel is left a short time. The lime absorbs the water, 
which of course disappears, great heat is evolved, and the lumps 
of lime shortly swell and burst into a most impalpable powder. 
The heap is opened and moved about with a hoe, to ascertain if 
the slaking is complete, or whether any solid lumps remain, re- 
quiring more water; if not, the mass is moved about to produce 
incorporation of the sand and lime, and if the process has been 
properly conducted, the whole will be found in a very nearly 
dry state, as the lime will absorb most of the water out of the 
sand, and any superfluous quantity will be driven off in steam, 
owing to the great heat of the mixture. The sifting or screen- 
ing now begins, and produces a most perfect mixture of the sand 
and lime, as they pass through the sieve together. The most 
convenient screen for this purpose, is one about six feet high 
and a yard wide, having projecting sides like a box, and covered 
by strong wire work, the wires of which are from a quarter to 
three-eighths of an inch apart. This screen is propped up, so as 
to stand at an angle of 45°, and the lime and sand are thrown 
against it by a shovel; what passes through it is fit for mortar, 
while all that falls in front will be either stones that were con- 
tained in the sand or unslaked lime, or pieces of the latter, which, 
for want of sufficient calcination, remain in the state of limestone, 



* ON BUILDING MATERIALS. 287 

and therefore are incapable of slaking. Such refractory material 
is called lime-core. 

All the fine stufi* that passes through the screen may now be 
made into mortar by merely adding as much water to it as will 
convert it into the proper consistency for use. The quality of 
mortar does not appear to be at all affected by the quantity of 
water added to it, provided it is not in such excess as to cause a 
separation, or subsidence of the sand from the lime. Indeed all 
mortar should be used in a rather wet and thin state, particularly 
for brick-work, because as bricks are absorbent in a greater or 
less degree, if the mortar is too dry, the bricks when laid upon 
it will take away a part of its water, and render it so dry and 
hard that it will be incapable of yielding to the weight of the 
brick, or even to any pressure exerted upon it, and the work 
will therefore not be so even and sound, as if the mortar had 
been in a thinner and more yielding state. Perfect contact, 
amounting almost to incorporation is necessary between the mor- 
tar and the brick or stone, and to produce it, it is advisable to 
dip each brick into water, as it is laid, or to throw buckets of 
water upon the pile of bricks as they are used, particularly when 
the season is very hot and dry; and it is always better to slide 
the bricks on to their mortar bed, than to put them down by 
direct pressure, whenever it is desirable to produce very sound 
work . 

518. It is generally admitted that the best and strongest mor- 
tar is produced from fresh or recently burnt lime, and for strong 
work, the sooner the mortar is used after it is burnt, the better. 
The reason of this may be, that when lime is fresh from the 
kiln, it is as completely deprived of its carbonic acid and hu- 
midity as possible, and is therefore in a more soluble state, and 
better suited for combining with water; and as mortar after it is 
made becomes re-converted into carbonate of lime, if exposed 
to the air, so the sooner it is used the better, because then its 
changes take place in the wall, instead of upon the ground. A 
quantity of quick-lime thrown down and exposed to tlie air will 
slake itself in a few days without any suffusion of water, because 
it will imbibe sufficient humidity from the air to produce this 
effect, and will fall to powder as effectually as if the slaking had 
been artificially produced; and lime thus spontaneously slaked 
may be made into mortar, but it will not possess the strength, 
tenacity, or durability of lime slaked by the quick artificial 
method. 

519. All mortar, made from the ordinary kinds of lime, re- 
quires to be kept tolerably dry in order to insure its setting pro- 
perly in the work in which it has been used; consequently it 



288 ON BUILDING MATERIALS. 

will not answer for use under water, or in wet positions. In these, 
a peculiar mortar called Cement, must be used; that is, a mortar 
composed of such materials as are capable of setting, or becoming 
hard very suddenly, so that if water is let in upon the building 
immediately after its completion, it will suffer no injury; and some 
of the best and most perfect cements will even set under water. 
The setting of a cement appears to be dependent entirely upon 
the materials of which it is composed, rather than on its mode of 
preparation, for that is merely burning it like ordinary lime; and 
no satisfactory explanation has ever yet been oifered of how the 
hardening takes place, or why one kind of earth should produce 
a lime so perfectly different and superior to another. It was for- 
merly believed that the effect was due to a certain mixture of 
metal with the limestone, and that it owed its character to the 
presence of iron, or m.anganese, or the oxides of these metals in 
the stone before it was burnt. Indeed, the French chemist 
Guyton de Morveau, in his early researches into this subject, 
came to the conclusion that all calcareous stones that produce ce- 
ment, or as it is very commonly called hydraulic lime, must 
contain manganese, and he gives a process by which such lime 
may be produced artificially, which is by mixing ninety pounds 
of common hard limestone with four pounds of pure dry clay and 
six pounds of black oxide of manganese, all in powder, and cal- 
cining the whole together, when, nothing but water will be ne- 
cessary to produce a good hydraulic cement. That the oxides 
of some of the metals do improve mortar, is well known to every 
workman; for it is a common practice, in England, for bricklay- 
ers to get the scoria from smiths' forges, (which is a protoxide of 
iron,) and after pounding it, to mix a little of it with common 
mortar, which not only makes it set quick, but become very hard. 
Mortar for pointing the joints of old brick work, is constantly 
made with this addition of oxide of iron. 

520. The material generally used in England as a cement for 
water-works, bridge building, lining tanks to make them water 
tight, and other similar purposes, is called Parker's cement, or 
Roman cement. Mr. Parker obtained a patent for the material 
and mode of preparing it, within the last half century, and he 
called it Roman cement, from a supposed resemblance that it had 
to a mortar or cement used by the Romans, and which is only 
known by its great hardness and apparently imperisliable nature 
in the ruins of their former buildings. Parker's cement was 
found so excellent, that it soon became an article of general con- 
sumption, not only in England, but in countries to which it was 
exported; and it is now known pretty generally over the world 
under the above names, or Wyatt's cement. Since the expira- 



ON BUILDING MATERIALS. 289 

tion of the patent it has been manufactured by many persons; but 
was always sold under its former names on account of their 
celebrity. This cement was at first manufactured from a natural 
boulder or pebble, found only near the Isle of Thanet, on the 
east coast of the county of Kent, and supposed to belong to that 
particular locality; but having since got into great request, it has 
been searched for, and is now ascertained to be one of the accom- 
paniments of the immense formation called the London clay 
basin, which extends to the sea-side in a north-easterly direction, 
and surrounds London in an almost circular form. The boulders 
were at first found on the surface only, having been washed out 
by the waters of the sea and the river Thames; but they are now 
discovered to be disseminated throughout this formation, which 
extends to several hundred feet beneath the surface of the soil, 
and they have also been found in other localities. The boulders 
are precisely similar in form and external appearance to those 
used for paving streets, and they vary in size from two to four- 
teen or fifteen inches in diameter; but, as they are not sufficiently 
hard for paving purposes, they were neglected until Mr. Parker 
discovered their valuable property of making hydraulic cement. 
On breaking them, they present a curious appearance, which is 
sometimes very beautiful; the body of the stone being a compact 
light brown argillaceous limestone that is dull or without polish, 
traversed by various veins of bright and highly crystallized 
white carbonate of lime, which cross each other in nearly right 
angled directions, so as to divide the stone into a number of septse 
or cavities, and give it an appearance similar to that shown by 
Fig. 125, Plate IV., which represents a section of one of these 
boulders. On account of their peculiar formation they are now 
called septarii by mineralogists, and in some of the older writers 
this stone is distinguished by the name of Ludus Helmontii. They 
have been found abundantly at Boulogne sur Mer in France, 
across the channel, and nearly opposite their first discovered lo- 
cation in England. See Journal des Mines, Vol. XII. These 
stones are broken and calcined in a dome or reverberating fur- 
nace, (510,) to convert them into quicklime. On leaving the 
kiln or furnace, they are as hard, or nearly so, as when they went 
into it, therefore this lime requires to be reduced, or brought into 
a state of powder, by grinding it in a mill formed of a pair of heavy 
stones called runners or edge stones. From this mill it is taken 
up as speedily as possible, and packed into close casks about the 
size of flour barrels. The casks are placed under a stamping ap- 
paratus while they are filling, by which the powdered cement is 
driven down with such force as to render it nearly as compact as 
solid stone; an expedient that is resorted to to prevent the ce- 
37 



290 ON BUILDING MATERIALS. 

ment being injured by exposure to air, which soon spoils it. 
The casks are then closely headed, and the material may be kept 
or transported without fear of detriment, provided the casks are 
kept in a dry place. In using this cement, a small quantity is 
taken out, and mixed with from four to five times its bulk or 
measure of very clean, sharp, and rather coarse sand, (such as 
passes the wire sieve, No. 30, (513,) is the best,) and sufficient 
water added to make it work, and the cement is ready for use. 
If the cement is fresh and good, no more ought to be mixed than 
can be consumed in half an hour; because in that time it ought 
to set, and become hard, and, consequentl}'^, unfit for working; 
and when once it is set hard, there is no method of reviving or 
softening it again. In many cases, where pure cement and sand 
would be too expensive for use, it may be mixed or incorporated 
with good fresh stonelime mortar, and even in the proportion of 
four or six to one, it will improve the quality of the mortar very 
sensibly. 

521. The celebrity of Parker's cement, and the scarcity, as to lo- 
cality, of the stone from which it is made, caused this cement to 
be very carefully analyzed and examined by many eminent Che- 
mists and Engineers; but still nothing could be discovered, fur- 
ther, than that the stones consisted principally of argillaceous 
limestone, that is, lime and argil, or clay, combined by nature, 
in the proportion of about two-thirds of the former to one-third 
of the latter, mixed with a small quantity of oxide of iron; and 
that the traversing veins were pure carbonate of lime; so that 
when an entire stone was reduced to powder, the quantity of clay 
or argil, was very nearly equal to that of the lime. This at once 
disproved the hypothesis of Guyton de Morveau, that all hy- 
draulic cement must contain a considerable portion of manga- 
nese. The composition of the Kentish boulder-stone, appeared 
simple and easy to imitate by art; and, accordingly, in 1818, M. 
Vicat of the Corps des Fonts et Chaussees, announced in a work 
he then published on the subject of limes and mortar, that he 
had succeeded in discovering a process by which all kinds of lime- 
stone whatever, might be cheaply converted into cement, or hy- 
draulic lime. His operation was truly synthetical, being derived, 
in the first place, from an analysis of the natural stone, by which 
he discovered the nature and proportions of its several compo- 
nent parts; and then, getting materials as nearly like them as 
possible, putting them together, and producing their union by 
aid of fire. 

522. The process consists in slaking the lime, and mixing it 
with pure or brown clay, and sufficient water to convert the 
whole into an adhesive mass, of which balls are formed; and 



ON BUILDING MATERIALS. - 291 

being dried in the sun, they are baked in a kihi, and produce 
lime of qualities entirely different from that at first used; which 
qualities are variable with different proportions of the materials. 
The clay is added in the proportion of from five to twenty per 
cent, to the lime for common purposes; but if forty per cent, is 
used, the mixture is said to become solid in a very short time 
after it is immersed in water. 

523. It has been before observed, that whenever raw clay en- 
ters into the composition of mortar, it is injurious to it; and M. 
Vicat remarks, that if the clay is baked alone, powdered, and 
added to the lime in any of the above proportions, it will mere- 
ly act as sand, without altering the character of the mortar; and 
that no benefit will result from the admixture of clay unless it is 
baked in combination with the lime, from whence he infers, that 
the fire acting at the same time upon the two substances, pro- 
duces some change in their internal arrangements, by which the 
character of the compound is affected, but what the real nature of 
this change may be, has never been satisfactorily accounted for. 
M. Vicat believes that a real chemical change and combination 
takes place between the lime and the clay. This subject has beea 
prosecuted with great energy and industry by several of the most 
distinguished Engineers and Chemists of France, and they all 
agree in the fact, that clay and lime burnt together, will produce 
hydraulic cement. M. Berthier states, that one part of common 
clay and two parts of chalk burnt together, makes a good hydraulic 
lime, and that all natural limestones that contain clay as a part 
of their composition, make much better mortar-lime than such 
as are pure. Many natural limestones are found that produce 
hydraulic cement. Thus the locks of the Great Canal in the 
state of New York, and the Union Canal of Pennsylvania, were 
both built with local limestone. And the Aberthaw lime of Lan- 
cashire, in England, is justly celebrated by Mr. Smeaton for its 
excellent hydraulic qualities. But the component nature of ce- 
ment was not understood in his time; and if these limestones 
were analyzed, there is little doubt but that their valuable pro- 
perties would be found to be dependent upon a certain quantity 
of clay, entering into the composition of the limestone. Lime- 
stone that contains but six per cent, of clay, is found to be per- 
ceptibly hydraulic; when it contains fifteen to twenty per cent, 
it is very good, and with from twenty-five to thirty per cent, 
the mortar sets almost instantly. This has been proved by 
Bruyere and Treussart, who assert that the free access of air during 
the calcination of argillaceous cements, is of great consequence to 
the tenacity of the mortar, and the quickness with which it 
hardens; and, therefore, that the common form of lime kilns is 



292 ON BUILDING MATERIALS, 

not the best for burning these materials; and, perhaps, as good a 
method as any for exposing them to heat is the reverberating 
furnace, described in the section on iron foundery, except that as 
the heat required is not so great as is necessary for melting iron, 
the width of the arch and floor may be considerably extended, 
and the well made much more shallow. 

524. Independent of the hydraulic cements above described, 
there are two natural substances which have been used to a great 
extent for mixing with mortar, in order to cause it to set under 
water, which are called Puzzolana, and Dutch Tarrass, or ter- 
ras. Puzzolana is evidently of volcanic origin, and is found in 
the vicinity of volcanoes. Its external appearance is that of a 
ferruginous clay that has been exposed to a high heat, having a 
great variety of colour, dependent probably on the heat it has 
undergone, and the proportions of the materials that enter into 
its composition, which by analysis are found to be clay, flint, 
lime, and iron. Mount Vesuvius has produced it in large quan- 
tities, and it is extensively found between Naples and Rome, this 
locality being the principal one from which it is imported to dif- 
ferent parts of the world for use. From its natural position it 
became known to the Romans, who, according to Vitruvius, used 
it very extensively, not only in their public buildings, but in 
erecting quays and other buildings in the w^ater, in the bay of 
Baiae, and as it was obtained principally from the town of Put- 
eoli, and was never used until ground to powder, it obtained the 
name of pulvis puteolanus; but as the best kind is now obtained 
from Puzzoles near Naples, the moderns have given it the name 
of Puzzolana. This substance when ground, sifted, and mixed 
with water, is capable of producing an hydraulic cement with- 
out sand; but on account of the expense of its transportation, 
it is always used with it, and frequently with lime also as a means 
of improving mortar and rendering it fit for water building. 
From the vicinity of Rome to the place where this material 
abounds, and is found in the highest perfection, it is very pro- 
bable that it formed a principal ingredient for the union of the 
stones and bricks used in the ancient Roman edifices, the strength 
and durability of which has so much excited the surprise of all 
the modern visiters and investigators. 

525. Tarras, or as it is very frequently called, Dutch tarras, by 
way of designating that of the best quality, was originally 
brought from Andernach near the Rhine, and possesses proper- 
ties similar to those of Puzzolana, in forming a compost with 
lime that hardens under water. It is believed to be a decompos- 
ed basalt of volcanic production, and in mass is so hard, that 
millstones may be made of it, and it is frequently used as a build- 



ON BUILDING MATERIALS. 293 

ing stone. When reduced to powder and mixed with lime, it 
forms the mortar or cement used by the Dutch, in their exten- 
sive sluices and other hydraulic works; and in that country such 
works are carried on to a greater extent than in any other nation. 
It is even probable that the Dutch were acquainted wuth the 
method of preparing artificial cements antecedent to the investi- 
gations of the French on this subject, for the privileged cement 
of Holland prepared at Amsterdam, and analyzed by Bergman, 
was of this factitious kind; but half its composition was silex or 
flint, and a very small proportion of it lime; the remainder being 
made up of clay and oxide of iron, in nearly equal quantities. 

526. These two materials are little known or used in the 
United States or England, since Parker's cement has become 
common, and the method of making artificial cements from 
native materials has been discovered and practised. Indepen- 
dent of which, there are many natural stones in this, and indeed 
in all countries, which, if tried and known, would yield good 
hydraulic cement. The young Engineer would therefore do 
well when he finds any stone or clay that he is unacquainted 
with, to test its quality for himself by actual experiment, which 
is very easily done, with no other preparation than a strong 
common fire, urged, if necessary, by bellows; or a smith's forge, 
should greater heat be required. If the earth be clay alone, it 
will, when previously dried, be converted by such heat into a 
hard insoluble mass in the nature of brick. Should the clay be 
pure, it will become white and hard, like common tobacco pipes; 
if less pure, it will turn red or brown; and should it become 
soft and friable, will be unfit for making bricks; while, on the con- 
trary, if it is not only hard, but withstands every heat that can 
be put upon it without fusion or vitrification, it will be fit for 
fire-bricks. If the mass should be burnt into a lime or cement, 
it will slake on adding water to it; in which case a quantity of 
it may be powdered, and made into a paste or mortar, which 
should be placed in the bottom of a bowl of water; and if, after 
standing a short time, it sets into a hard insoluble mass, it will 
be a water cement, while, on the contrary, should it continue 
soft, it can only be regarded as common mortar. 

527. A very clear idea of the manner in which these hydrau- 
lic cements set and become hard, may be derived from noticing 
what takes place with Plaster of Paris, which is a lime made by 
burning as before described; but the stone burnt is sulphate, and 
not carbonate of lime. Plaster stone, as the raw material is 
usually called, retains its solid form after burning, and will not 
slake or fall to powder on the addition of water. The burnt 
stone, therefore, requires to be ground to powder in a mill, and 



294 ON BUILDING MATERIALS. 

in that state is called Plaster of Paris. On mixing water with 
this powder, heat is produced, though in a less degree than with 
quick lime; and a paste or mortar may be formed without sand 
or any other ingredient, that will adhere to bricks or stone; but 
it must be very speedily used, for in less than a quarter of an 
hour the paste will become hard and compact, even under the 
presence of a superabundance of water, and in a short time after- 
wards will assume a stony hardness. It might therefore be 
supposed, that this material would supercede the necessity of 
searching for any other cement, but it is found inapplicable to 
the common purposes of cement: first, because in setting, it 
swells or augments in its dimensions to such an extent as would 
disturb the regular form of stones or bricks set in it, if used in 
large quantities; and secondly, it is perishable, or decomposes by 
the continued action of air and water, in which particular it is 
quite opposite to limes made from good limestone, for they in- 
crease in strength and hardness by time, even in wet or damp 
situations. It is therefore much more difficult to pull down an 
old, than a recent wall, if it has been built with good mortar. 
Plaster of Paris is however a very useful building material for 
many internal and ornamental purposes, where it is not exposed 
to weather. It is the mortar or cement constantly used by 
marble workers for uniting the parts of marble in chimney pieces 
and other ornaments. It enters into the composition of plaster- 
ing for ceilings and walls; and from its property of setting hard 
even when mixed with such an excess of water as will render it 
fluid enough to run into hollow moulds, it is extensively used 
for casting plaster figures, enriched cornices for rooms, orna- 
ments for ceilings, and many similar purposes. 

528. Another kind of mortar is much spoken of by the 
French Engineers, under the names of Concrete and Beton, 
and it has also been called gmh-stone mortar. It is very little 
resorted to in England, and is not w^orthy of being treated under 
a separate head, because it is nothing more than any of the hy- 
draulic cements rendered more hard, solid, and capable of filling 
up hollow spaces, by being mixed with small fragments or chips of 
any hard stone, or even with gravel pebbles. It is rather an appli- 
cation of mortar or cement, than one possessing distinct and sepa- 
rate characters from others, and in this respect it may class with 
^roz^/ or liquid mortar, therefore an account of the use and applica- 
tion of both these maferials will be reserved for the chapter on 
masonry and brick-work, when their use and applications will 
be pointed out. 

529. It has been before observed, that the more mixing, beat- 
ing, or chafing mortar receives, the better it is, not only to work, 



ON BUILDING MATERIALS. 295 

but for the solidity of the work done with it; and when so treat- 
ed, every lime will bear a larger proportion of sand without 
detriment. But as the proper beating of mortar is hard work, 
there is often great difficulty in getting the labourers to attend 
properly to this business. In all large concerns where a con- 
siderable quantity of mortar is required, it is therefore better to 
employ a mill worked by a horse, to produce the due incorpora- 
tion of the materials, than to trust to hand labour: and the kind 
of mill generally used, is in form and construction exactly like 
the pug-mill before described, (400,) Fig. IIS, Plate IV,, 
with the exception only of the rakes or cutters which require to 
be of a different form, because there are no lumps, or any thing 
solid to be divided or broken in mortar, all that is wanted being 
a perfect mixture and incorporation of the materials. This may 
be brought about by a number of oblique scrapers or revolving 
shovels, like f in Fig. 119, or by alternating these with rakes, 
such as are shown in the figure, but in which the teeth are 
smaller, closer together, and upright, instead of oblique. When 
a mortar mill is used, the lime is slaked and mixed with the sand 
and some water, as if it was about to be made in the ordinary 
way, but it is left sufficiently dry to admit of its being conveyed 
in barrows without loss, and the remaining quantity of water to 
render it thin enough for use is added in the mill. 

530. Another form of mortar mill is shown at Fig. 126. It 
consists of a large and strong wooden wheel or cylinder A, which 
is maintained in its vertical position by an axle running through 
the wheel, and which is a continuation of the timber arm i, the 
end of which, nearest to i, passes through a morticed hole in the 
upright revolving post k, so that the cylinder h is constrained to 
move in a circle round this post, which circle is formed of brick- 
work with sloping sides, in the form shown in section at //, and 
motion is given to this cylinder by attaching a horse at m. The 
two sides of the cylinder are closely boarded to prevent any 
mortar getting into the inside of it, and its breadth should be 
very nearly equal to that of the bottom of the circular channel //, 
into which the lime, sand, and water are introduced in due pro- 
portions. As the cylinder revolves it presses the materials before 
it, and raises them up in the two cavities / /, from whence they 
fall behind it, and the mortice joint at z, permits the cylinder to 
rise and fall for passing over the materials if they are unequally 
distributed. The horse is placed within the channel / /, for the 
purpose of keeping the outside of it constantly clear and open 
for the workmen to come and fetch mortar from all sides of the 
circle, or for introducing fresh materials. Cement may be mixed 
in a mill of this kind, provided a great quantity of it is wanted 



296 ON BUILDING MATERIALS. 

in a short time, otherwise it is always better to mix it by two or 
three shovels full at a time, as rapidly as it is consumed. Most 
of the cements work short under the trowel, or are wanting in 
the tenacity that belongs to well made mortar, and they are con- 
sequently more difficult to apply. 

531. Of late years, an oil cement has been introduced in Eng- 
land, under the name oi mastic, which is particularly well suited 
to forming external mouldings and ornaments, or for plastering 
exterior walls to protect them from humidity, but it is not suited 
for the joints of walls unless a great additional quantity of oil 
should be used, which would render it too expensive. It is a 
French invention, and has given great satisfaction wherever it 
has been used, but works in so short and brittle a manner that it 
requires experience in the workman who applies and uses it. 
It is composed of very clean and sharp sand, mixed with about 
a twentieth part, by measure, of slaked stone-lime in powder, 
and a sufficient quantity of red-lead and litharge, to insure its 
drying. These ingredients are carefully incorporated together, 
and at the time of using them are mixed with as much linseed oil 
as will barely convert the dry powder into a paste. The oil 
should not be in greater quantity than about three or four quarts 
to a hundred pounds weight of the dry powder, and the wall or 
other surface to which it is to be applied must be perfectly dry. 
Mastic will adhere to brick, stone, slates, lathing, glass, and even 
wood, if properly applied, but it is necessary to lay a coat of the 
same oil upon the surface a day or two before the mastic is applied, 
in order to insure its adhesion. 

The methods of using mortar and cement will be described in 
the chapter allotted to masonry and brick-work. 

Section III. — Of Tiinbcr, 

532. One of the most useful and important of the materials 
for building is timber, but as the means of using and converting 
it constitute the art of carpentry, to which a separate chapter is 
appropriated, and such observations as are necessary in regard 
to its strength and mode of application, will be found in the 
tenth chapter, so nothing more is required in the present sec- 
tion than to give an account of the varieties of timber generally 
made use of, and the forms into which it is cut to render it avail- 
able for building purposes, and to show the manner in which it is 
measured, or its quantity ascertained while in the rough or un- 
wrought state. 

Timber is the production of nature, being the stems or trunks 
of trees, and it requires no other preparation for the builder's pur- 



ON BUILDING MATERIALS. 297 

pose, than seasoning it, and cutting it into the necessarj^ forms. 
The seasoning of timber is an object that requires particular at- 
tention, because the goodness and durability of the timber is 
materially influenced by it. By seasoning is meant the gradual 
dissipation of the natural juices of the plant, by which it becomes 
dry and fit for working. These natural juices are the sap, or 
food, or nutriment of the plant, imbibed by the roots from t] 3 
earth, carried up the stem or body, and distributed through the 
branches to the leaves, by a series of most minute tubes or ves- 
sels, by which the distribution is rendered very general. This 
sap is frequently sweet to the taste, and contains much saccharine 
matter, is generally fermentable, and is found by experience to 
be much more detrimental to the duration of the wood than pure 
water. The sap is thought by many to circulate, that is, to rise 
into the tree at one season and descend from it in another; but 
the probability is that it moves in one direction only. It is 
known to rise in the spring, when its elevation and presence are 
necessary in the upper part of the tree, for the production of 
young shoots and leaves; and it continues to flow as long as the 
leaves are augmenting in size, or fruit is forming. But when 
once these have attained their full size and maturity, there is not 
the same occasion for nutriment, and the supply becomes less 
abundant, or in all probability stops entirely when nature no 
longer requires it. At all events, whether the sap rises and falls 
again, or whether it flows abundantly at one season of the year, 
and not at all at another, there are periods in which every tree 
is much more full of sap than at others; and as it is desirable to 
have all timber for construction as free from sap as possible, this 
at once points out that one season is more favourable than another 
for cutting or felling timber, and the most favourable of all is 
winter, up to the period when the appearance of buds or young 
leaves first bursting forth indicate that the sap must be rising 
for their developement and growth. So soon as the leaves ap- 
pear, and during the summer, no trees ought to be cut down for 
timber, for then they are more full of sap than at any other time. 
When the leaves have attained their full size and vigour, about 
the month of July, timber may also be cut, because then the 
leaves carry ofi' the sap as fast as it is brought up, but afterwards 
when they do not require so much nutriment, or even begin to 
decay, the draught upon the trunk diminishes, and it is again 
found full of sap. Hence the only seasons at which trees should 
be cut down for timber, are the winter, and close of summer, 
and experience gives a preference to the former period. 

533. The trunk or body of a tree is composed of three parts. 
The pith in the centre, the wood which surrounds it, and the 
2>^ 



2&8 ON BUILDING MATERIALS. 

bark which forms the case or external covering. When a young 
tree or a shoot first grows, the pith is of large dimensions, and is 
surrounded by a narrow cylinder or casing of wood, and that is 
covered by a thin bark. The secretions of the tree are perform- 
ed principally by the bark, or between the bark and the wood, 
and there it is that the portion of sap or vegetable nutriment 
destined to form w^ood is deposited. The process goes on during 
the summer, but is suspended in the winter season. But when 
the spring returns, a new portion of wood making sap, is brought 
up and deposited between the bark and the last year's wood, form- 
ing a new layer or hollow cylinder of wood, which, while it ex- 
tends the bark, and causes it to crack and become uneven by re- 
newal, compresses the former formation of wood, and renders it 
more close and compact. This process is renewed every year, 
in consequence of which, the body and branches of trees when 
cut transversely through, exhibit a series of rings, by which the 
years of its growth may be counted. These rings are only con- 
centric in close forests, where the wood is little exposed to the 
sun's heat and light; but in open or single trees that enjoy these 
advantages to the full extent, the \y.ood is always more thick 
and better developed on the south side of the tree. The pith 
never enlarges, and though very large in proportion to the quan- 
tity of wood in the first year's growth, probably becomes nearly 
useless afterwards, and being compressed by the growth of the 
surrounding wood, nearly disappears, and as the tree approaches 
maturity, bears no sensible proportion to the quantity of the wood 
surrounding it, so that the tree may then be said to consist of two 
parts only, viz: the wood and the bark. The w-ood from the 
nature of its formation, varies materially in difierent parts, for 
as the central rings are the oldest and most condensed, so, like- 
wise, they are the hardest, most compact, and durable, and this 
part of the tree, or of the timber cut from it, is distinguished by 
the name of heart. For the same reason, as a tree begins to 
grow from the ground, the lowest extremity of it next the root 
is older, and more compact than the wood produced in the upper 
part, and is the most valuable part of the timber for use. This 
at once shows the impropriety of cutting timber in the manner 
practised in the woody part of this country, so as to leave stumps 
of from two feet to thirty inches high standing in the ground. 
The argument is, that timber is so plentiful, that the waste of 
this quantity is not important, or worth putting into competition 
with the inconvenience the woodman would suffer from having 
to stoop to make a low cut. But the great evil is, that two or 
three feet of the best timber in the whole tree is thus thrown 
away J and a part that is least likely to rot and decay, is left upon 



ON BUILDING MATERIALS. 299 

tlie land. For the same reasons that the central part of a tree 
furnishes the best timber, so the external part is the worst, for 
its last layers or rings can only be a few years old, and they 
(especially the last one) have their sap vessels large, and full of 
the circulating juices of the tree, in the operation of dispensing 
which, they co-operate with the bark; and hence this external 
wood is denoted by the name of sap^ when speaking of timber, 
and this part of the wood is not only soft, but liable to very 
speedy decay, on account of its spongy and absorbent nature, 
and the great quantity of natural sap, saccharine matter, and gum 
with which it is always charged. The external bark contains 
nothing that is valuable for the purposes of building, and there- 
fore need not be regarded. 

534. From the above account it will be seen that two prin- 
cipal objects present themselves to the consideration of the pro- 
ducer of timber, one of which is, to diminish as far as possible, 
the production of this soft and worthless external sap-wood; or 
if produced, to harden and ameliorate it; and the other is to 
discharge and get rid of the natural juices of the tree, so as to 
render it dry, hard, and not liable to internal decay, and make 
it fit for the purposes to which it is to be appropriated. The first 
of these has been attempted to be attained by what is called 
girdling and harking the tree, while growling; and the latter is 
called seasoning, and cannot be commenced until the tree is cut 
down. 

535. Girdling is making a deep incision entirely round the 
tree, near to its root, by means of an axe, so as to sever the sap 
vessels, and destroy any communication through them, between 
the root and upper part of the tree; and to do this effectually, 
the incision should not only pass through the external bark, but 
extend some depth into the sap-wood; and barking is the strip- 
ping off and removal of the bark from the external surface of 
the trunk of the tree while yet growing. 

536. Both these expedients are of great antiquit}'", for Vitru- 
vius and other old writers say, that the density and strength of 
wood is much improved by causing the tree to die standing, in 
consequence of resorting to either of these processes; and Du- 
hamel and Buffon tried many experiments to ascertain the truth 
of this assertion, and which of the two methods might be most 
beneficial to the timber. The result was unequivocal; for a de- 
cided superiority was given to the timber in both cases, but the 
advantage as to the quantity of real sound timber obtained was 
greatly in favour of the barking operation. It was found that 
when a tree was girded to a sufficient depth, its death very soon 
followed, and of course no further natural change ensued. The 



300 ON BUILDING MATERIALS. 

timber was therefore obtained in very nearly the same state as to 
its external rings, as it was in when the girdling took place, ex- 
cept that they became partially dried and seasoned. By barking, 
on the contrary, the death was not so sudden, and the sap-wood 
almost disappeared. BufFon states that some oak trees thus treat- 
ed, showed no symptoms of disorder until about four months after 
the bark had been removed, and then their leaves became yellow 
and fell. Some of these trees were left standing until the follow- 
ing summer, and in the spring their leaves shot forth as vigor- 
ously as if the tree had not been injured, but they languished, 
did not come to maturity, and soon fell. This last efibrt of vege- 
tation must have been carried on through the sap-wood, and 
therefore it might reasonabl}^ be expected that some physical 
change should take place in it, and on cutting down the trees, the 
sap-wood was found to have almost disappeared, or rather it was 
so changed in its nature, that it could not be distinguished from 
the wood of the heart. It had become dry, hard and compact, 
and was to all appearances as good, though not quite so heavy, 
bulk for bulk, as the wood in the centre; and in the experiments 
tried with it, it was evidently improved in strength and tenacity. 
The weight of equal masses of oak timber that had been barked, 
was greater than those felled in the ordinary manner, and the 
strength of the one was to the strength of the other as 81 to 74. 

537. These experiments, and others that have been tried, show 
a marked advantage from barking trees at the period of full 
growth and vigour, when they are intended for timber, and let- 
ting them stand at least one year after the operation. In this 
way, the sound wood is not only improved in quantity, but in 
quality also, and at the same time it undergoes a partial seasoning, 
under circumstances very favourable to that process. It is often 
resorted to in England, and other parts of Europe, especially 
with oak trees, not so much perhaps with a view to the improve- 
ment of the timber, as on account of the demand for oak bark 
by the tanners, and the timber is often unintentionally improved 

■ in this way. 

538. The seasoning of timber requires great care and atten- 
tion, and is better effected by time than by any artificial method. 
It consists of getting rid of the natural juices of the wood, but 
if they are dissipated too rapidly, the timber will crack, and 
become so full of flaws, or shakes, as they are called, that it may be 
greatly diminished in value, or may be rendered useless; on the 
contrary, if the natural moisture is permitted to remain in it, it 
will undergo partial decomposition, or decay, particularly on its 
outside, if the bark is permitted to remain upon it. The bark 
should therefore bo speedily removed, and if the timber is want- 



ON BUILDING MATERIALS. 301 

ed in a square form it will also be necessary to hew it roughly 
into that shape, by which a great proportion of the sap-wood will 
be removed, thus affording better egress for the humidity from 
the heart of the tree. On this account squared timber always 
seasons more favourably, and with less injury than that which 
is round. 

539. Timber is generally brought from the countries that pro- 
duce it by water carriage, but instead of loading it into dry ves- 
sels it is made into rafts, or placed in craft that are not particu- 
larly water tight, provided it has not to be carried over the seas. 
This mode of conveyance is not adopted for economy alone, but 
to produce seasoning, since nothing contributes more effectually 
to this purpose, than soaking timber for some time in fresh water. 
The water dissolves and incorporates with the natural fluids of 
the wood, which are thus removed, and the water takes their 
place; and as the water is not viscid, and so corruptible as they 
are, it is more easily evaporated, and does not prove so injurious 
to the timber. Timber that is imported into foreign countries, 
must, however, be carried in close vessels, because if it imbibed 
sea water, its salt is deliquescent, and such timber would require 
a great length of time to dry, or it might never become perfectly 
dry, and therefore unfit for all the purposes of sound and dry 
work. Timber brought by sea is usually discharged into fresh 
water rivers, where it is formed into rafts, and kept a consider- 
able time before it is sawed or converted to use. 

540. In places that do not offer the advantages of water steep- 
ing, and where squared timber has to remain upon the ground, 
it may be piled one log upon another; but the logs ought never 
to be in contact with each other, or with the ground, unless it is 
intended for immediate use, as this is apt to produce decay or 
dry rot, particularly in recent timber. A small opening between 
one log and another, and between the ground and those at the 
bottom, should always be left so, to insure a free circulation of 
air; and this is easily efiected by putting sticks or short timber 
between them. No protection against rain will be necessary, for 
that does good; but the logs should be screened from the effects 
of hot sun by putting them in shady places, or covering them 
with boards. 

541. When logs have remained a sufficient time in the water, 
they should be drawn on to dry land a day or two before they 
are sawed, in order to dry them, and make them more fit for 
work. This however produces no advantage to the timber, and 
as it gives additional trouble, it is seldom attended to, and the 
logs are most commonly drawn directly from the water to tlie 
saw-mill, or saw-pit, where they are cut to any required dimen- 



302 ON BUILDING MATERIALS. 

sions. It is then that the timber receives Its last and final drying, 
for when cut into planks or scantling, the quantity of surface 
is so much increased, that evaporation now goes on very rapidly; 
so rapidly indeed that it requires checking, by placing the cut 
timber in places where it is not exposed to the action of wind or 
sun. The boards or pieces should be placed with intervals be- 
tween them, for the reasons before assigned, and the triangular 
mode of piling, with the end of one board or piece resting on 
the others, is very convenient, as it forms spaces for the air to 
pass through, and affords security, as the top pieces only can be 
moved, and the pieces are very easily counted. 

542. Different soils, climates, and exposures, occasion very 
sensible differences even in timber of the same kind. Thus the 
timber of hot and humid countries is of very rapid and luxu- 
riant growth, and is seldom hard and good, while that of colder 
regions has an opposite character. In general, those trees that 
are of the slowest growth, and take the longest time to come to 
maturity, yield the strongest and most durable timber. But 
this is not a general rule, for some hard woods of slow growth, 
belong to warm climates, and the torrid zone produces a few of 
the hardest woods known. Knots in timber are occasioned by 
the pushing forth of branches from the trunk or main limbs of 
a tree, and they always produce contortions of grain with in- 
creased hardness, in their immediate vicinity, notwithstanding 
which, they greatly impair the lateral strength of a piece of 
timber. The production of knots depends very much upon the 
place where a tree is grown; for all vegetables require air and 
light, and should they be deprived of it, will seek it out most 
mysteriously. In close forests when the trees shade one another, 
the timber is constantly tall and straight, because trees so placed 
naturally shoot upwards in search of air and light, and as such 
positions are unfavourable to the production and growth of side 
branches, they seldom occur either in great numbers, or of much 
magnitude; consequently, the timber of such trees will be long, 
straight grained, and free from knots, or at any rate from large 
ones; and when timber or planks are thus clear from blemish or 
imperfection, they are, in the language of carpentry, said to be 
clean. The best white American pine timber, affords a good ex- 
ample of this variety. It grows to great length and width, and 
is so perfectly clean, or free from knots, inequalities of grain, or 
other imperfections, that it is almost exclusively used in England 
for ornamented doors, mouldings, and internal fittings of the 
best houses. 

543. As to the kind of timber selected for building purposes, 
that must depend upon the facilities of the country for obtain- 



ON BUILDING MATERIALS, 303 

ing it. In this respect England and America present a striking 
contrast. The British isles being of small extent, and England 
in particular being highly cultivated for agricultural purposes, 
cannot be considered a timber growing country, it being found 
more profitable to use the land for raising live stock, and grain, 
than timber. The few forests that remain in it are considered 
as part of the royal domain, and are reserved only for the culti- 
vation of oak for ship building, and that generally of the crook- 
ed kind, for knees and other parts of vessels requiring curved 
timber. The pine is almost unknown? except in pleasure shrub- 
beries and plantations, but the elm, the straight oak, and the 
beech are very common. Notwithstanding the paucity of pine 
in this country, that is its standard timber, and almost the only 
one that is used in houses, and all ordinary constructions. This 
timber is all imported from Riga, Memel, Dantzic, and other 
ports in the Baltic and north of Europe, for strong and external 
purposes, and from America for internal and ornamental work, and 
all goes under the common names of white and yellow deal. Oak 
is used for purposes where greater strength and duration are re- 
quired, and this is only known to builders under two varieties, 
called English oak, and wainscot, the latter being an imported 
wood, of a handsome grain or texture. English pine and pop- 
lar, are small and soft, and held in no estimation; but the beech 
and elm grow very large, and the former is a very close grained 
and hard wood, of superior quality, and is very durable under 
water, and useful in the construction of tools and machinery. 
Mahoghany is an imported wood that is extensively used for 
furniture, doors, handrails of stairs, and other fittings^ in the 
most elegant and expensive buildings. 

544. America, on the contrary, was but a few years ago an 
almost universal forest, and will continue to yield a most plenti- 
ful supply of timber, in every variety, not only for her own 
wants, but for exportation to foreign countries, for years to come. 
The oak and pine exist here of many species, though but few of 
them are used for the general purposes of construction. A very 
fine and compact oak that is exceedingly hard and durable is 
found in Virginia, and is called there post oak, probably from 
the circumstance of its being a straight grained timber that never 
reaches a very large diameter. But the white barked oak, or 
white oak, grows generally very large, and is chiefly resorted to 
for large framing, and heavy machinery, for which it is a most 
excellent material. The pine also exists in many varieties, but 
is distinguished, as in England, into twc^ sorts, the white and 
yellow. White pine is the kind chiefly exported to Europe. 
It derives its name from the colour of its wood, which is a very 



304 ON BUILDING MATERIALS. 

light yellow inclining to white. The wood is very soft and clean; 
it is very absorbent of humidity, and therefore liable to great ex- 
pansion and contraction in wet and dry weather; but, notwith- 
standing this, it is durable, particularly for inside work, and 
being nearly free from turpentine, or resinous matter, it works 
well with the plane, and is an excellent wood for holding by 
glue, although a very bad one for retaining nails. This material 
is the white deal of England, and grows chiefly in the northern 
states of America. 

545. The yellow pine, on the contrary, is very full of turpen- 
time, insomuch, that it will frequently ooze from the surface 
of the wood when cut, even though it may have been long sea- 
soned, and the excess of this material gives the wood a reddish 
yellow colour, from which its name is derived. It is much more 
strong and durable than white pine, as the turpentine it holds is 
a great preservation of the wood, and renders it very slightly 
absorbent of water. It is much used for building and strong 
framing, attains large size, and is a most useful and valuable 
timber, though not well suited to small and neat work. 

546. Hemlock is another variety of fir, agreeing very nearly 
with the Memel and Bruwick timber imported into England. 
It occurs in large logs, but is much more knotty and coarse in 
its grain and appearance than the other pines. It is very strong 
and durable, and may be used with advantage in roofs, girders 
or any places in which whole, or unsaw^ed, or large timber is 
required, but does not answer so well to cut into boards or small 
scantling, on account of its knots and inequalities, which render 
it difficult to plane, and render it uncertain as to its strength. 

547. In addition to the above timbers, which are used in com- 
mon, both in England and America, the latter country has its 
locust, red and white cedar, Cyprus, live oak, and several other 
useful varieties. The cedars and cypress are much esteemed 
for their durability, and resistance of decay from humidity, and 
are therefore much used for foundation work, posts to be insert- 
ed in the ground for fences, and likewise for the shingles with 
which almost every house and building in this country is cover- 
ed; the cypress grown in the swamps being preferred for this 
latter purpose. The live oak is a very peculiar tree, hitherto 
found only in the south-eastern states of this country, and then 
only upon and within a few miles of the sea coast. Like all 
other trees growing near the sea, it never attains high growth, 
but is occasionally of considerable diameter. It affords a very 
fine grained and comp{K',t wood, which is harder and more dura- 
ble than any other kind of oak, and is interesting to the Engi- 
neer and mill-wright, because it is found particularly well suited 



OF TIMBER. 305 

for the formation of the wooden teeth or cogs of mill wheels. 
Formerly a very hard wood called hor^nbearn, was used exclu- 
sively in England, for this purpose; but of late years, consider- 
able quantities of live oak have been exported, and it is much 
esteemed by all who have given it a trial. It is also an excellent 
material for ship building, and for all purposes where a compact, 
hard, and durable wood is desirable. Dog wood is a very valu- 
able material for many purposes, particularly for turning, and on 
this account is much used for the formation of all turned or round 
patterns, for casting iron or brass from, as will be explained in 
the next section. 

548. Timber, or lumber as it is generally called in this coun- 
try, obtains different denominations, from the manner in which 
it is cut or prepared for use. Thus, when a tree is cut down, 
the top and lop, consisting of all the branches are cut off, as well 
as the small top end, and these parts in England where wood is 
scarce, are again cut up into two varieties, called billet d^ndi faggot 
wood. The billet wood consists of the larger branches divided 
into four feet lengths, and is synonymous with the small or unsplit 
cord wood of this country, and is used for the purpose of fuel; 
and faggots are the small branches and twigs, cut to two feet 
lengths, and tied into small bundles for kindling fires. The quan- 
tity of top to be cut away from a tree, is regulated by the circum- 
ference; for nothing is called, or considered timber, that has a 
less girth or circumference than 24 inches. The body of the 
tree thus left naked, is called a stick of round timber. If four 
of its sides are hewn or chopped to such an extent only as not 
to render it square, but with an octagonal section, consisting of 
four flat and four curved sides, it becomes a baulk or log of rough 
hewn timber; but if the hewing has proceeded to such an extent 
as to have made it quite or nearly square, then it is called a die 
square stick or piece of timber; and all timber ought to be reduc- 
ed to this form by hewing or sawing before it is sawed or divided 
into smaller pieces. These several denominations are not affected 
by the length of the pieces. 

549. Timber is divided into smaller pieces by sawing; an ope- 
ration that was formerly carried on by hand labour only, but 
which is now better and more cheaply and expeditiously per- 
formed by the saw mill; so that hand-sawing is only resorted to 
when the convenience of the mill cannot be obtained. If a stick 
of round timber is sawed, the pieces taken from its two opposite 
sides will be flat on one of their sides, and will partake of the 
rotundity of the tree on the other, and such pieces are called slabs. 
They are not of much value, on account of their round side, rough 
edges, and their being external, and consequently sappy wood, 

Z9 



306 ON BUILDING MATERIALS. 

but are used for covering drains, making temporary fences, and 
they are occasionally, though improperly, put for planking under 
the foundations of brick and stone walls. 

When timber is cut or divided, it has different names applied 
to it, depending upon the size and form of the pieces so produced. 
Thus, when a stick of timber is sawed longitudinally, so as to 
produce a number of plates of timber, the sides of which are pa- 
rallel to each other, such plates are called planks or boards, which 
names are applied according to their thickness. Every piece 
that is two inches thick, but does not exceed four or five inches, 
is called a plank; and planks are distinguished by their thick- 
ness, length, and species of timber. Thus we have 2 inch 
pine plank twenty feet long; and the various kinds of plank are 
thus designated, by always naming the thickness, length, and kind 
of wood; and the thickness always varies by half inches, so that 

2 inch, 2^ inch, 3 inch, 3^ inch, 4 inch, 4-|^ inch, and 5 inch 
plank constitute all the varieties. In England pine planks of 

3 inches thick are called deals, consequently, whenever deals 
are mentioned in quoting prices in British newspapers, or price 
lists, this dimension is always understood ; the length of the planks 
being generally added, and the place they come from, by which 
their quality is in some measure known. Thus 20 feet Christiana 
deals, would indicate 3 inch planks, each 20 feet long, from 
Christiana in Norway, and as that place always sends a superior 
kind of plank into the market, they fetch a higher price than 
deals from other countries. In describing pine planks or boards, 
it is also necessary to state whether they are white or yellow, 
and clean. 

550. Any parallel plate of timber less than two inches in thick- 
ness, is called a board, consequently there are quarter inch, half 
inch, three-quarter inch, inch, &c. boards, until the thickness 
reaches two inches, when the board would be called a plank. If 
no thickness is specified for a board, one inch is always imder- 
stood; so that if a carpenter was desired to board up a partition, 
or other piece of work, he would of course use boards one inch 
thick. Flooring boards are, however, always considered to be 
one inch and a half, or one and a quarter thick, and would accord- 
ingly be so used, unless directions were given to the contrary. 
Boards are frequently sawed out of whole sticks of timber, but 
the best are those that are produced by sawing planks, because 
boards ought to be well seasoned before they are used, and nothing 
seasons timber more effectually than keeping it in a state of plank 
for a considerable time, before it is subdivided into thin boards. 
It is likewise a common practice in this country to produce planks 
or boards at once out of round timber, when of course the edges 



OF TIMBER. 307 

of the thin pieces will be rough and ragged, partaking of the ori- 
ginal rotundity of the tree. Such planks or boards are called 
rough edged, and in measuring them, the purchaser has the right 
of deducting as much from the quantity as will convert them 
into square edged stuff, because all planks and boards should be 
sold with straight and square edges, which can only be produced 
in the first instance by converting the round log of timber into 
the die square form, before the sawing process commences. 
When a piece of timber or a plank is sawed into boards, particu- 
larly when they are thin, each board is called a leaf, from the 
resemblance to a book, so that if five cuts are made in a three inch 
plank, it will convert it into six half inch leaves or boards. Some- 
times the cuts are not all parallel to each other, but the board pro- 
duced is made one inch wide on one edge, and only half an inch 
at the other, as when boarding is wanted for covering the sides 
of frame buildings, and it is then called feather edge or weather 
hoarding. The best floors are laid with battens, which is the 
name of narrow boards being from 3 to 6 inches wide, cut out 
of the heart or best of the timber, and they are consequently free 
from sap. The best battens are likewise clean or free from knots, 
and are, therefore, the best and most expensive kind of boarding. 
55 1. When timber is cut in two longitudinal directions at right 
angles to each other, so as to leave the corners square, the pieces 
are called scantling, or quartering, which last term was probably 
derived from the entire stick of timber being cut into four quar- 
ters, by being first slit down the middle, and each half being 
again divided. Scantling is, however, any thing that is above 
two inches square, and less than a whole stick of timber; and it 
is always designated by the dimensions of its sides. If one di- 
mension only is given, then all sides of the piece are alike. Thus 
2 inch, 3 inch, or 4 inch scantling imply a long piece of timber, 
each side of which measures two, three or four inches, conse- 
quently it is square. But if the two sides differ, their two dimen- 
sions must be given, as 4 by 2 J inches, or 3x6 inches, &c. ; this 
imports that its two opposite sides each measure the same, so that 
it will have two sides 4 inches wide, and the other two 2\ inches. 
Four by two and a half inches is the most usual size of scantling 
used in brick buildings, because it is the same size as the end of 
a brick, and therefore works in very conveniently with brick- 
work. For this reason scantling of this size is commonly called 
regular quartering, and is the kind of material almost constantly 
used for the common rafters of roofs, and for lath and plaster par- 
titions between one room and another in a house. Such parti- 
tions are frequently called quarter partitions by workmen, on 
account of their being formed of quartering. 



308 ON BUILDING MATERIALS. 

552. In addition to the above forms into which timber is cut, 
some of the most valuable and expensive woods are divided into 
very thin leaves, varying from the tenth to the twenty-fourth of 
aa inch in thickness, when they are called veneers, and are used 
for ornamenting furniture, and doors, by glueing them upon the 
surface of the thing to be ornamented, when it is said to be 
veneered, and this term is frequently used in opposition to solid 
w^ork, which means work made of the same kind of wood through- 
out, and it is, therefore, more substantial and durable. 

553. Timber when cut into any of the forms above described 
has the general name of rough or unconverted timber, and in this 
state it is always sold by measure to the carpenter, builder, or 
consumer; and in pursuance of the observation made at the close 
of Chapter III. (210,) this subject will be concluded by practical 
directions for measuring the several forms of timber, an opera- 
tion that should always be performed on receipt of it upon the 
work, or before any part of it is used or converted. 

554. The practice for round timber, that is whole trees, before 
they are squared or hewn, is to take one quarter of their mean 
circumference. The circumference in timber measuring is called 
the girt of the tree, and consequently a fourth of it will be its 
quarter girt, a term quite familiar to those who are in the habit 
of measuring timber, and it is usually obtained by straining a 
string, strap of leather, or cord round the tree, and afterwards 
doubling it in four equal parts; the length of one of which is then 
measured in inches by a common inch ruler. A better way is to 
take the girt with a measuring tape (373) in inches, and divide 
the quantity by four, because if the string is large a loss of its 
length will occur at each fold. 

Any part of a tree that is less than two feet round, or six inches 
in the quarter girt, is not deemed timber, and consequently m.ust 
not be measured as such. If a tree tapers regularly from end to 
end, its girt may either be taken in the middle, or half the sum 
of the girts at the two ends may be used to obtain the quarter 
girt; but when the tree does not taper regularly, or if it contains 
branches or arms, it must be divided into two or more parts, the 
dimensions of each of which must be taken separately. In some 
cases, where from the irregular form of a tree a difficulty may 
arise as to the proper girt, the position is settled between the 
buyer and the seller, previously to taking the dimension. When 
trees are measured with the bark upon them, an allowance is 
made for it. In oak and elm the deduction is at the rate of an 
inch in the foot, from the quarter girt; ash, beech, and such trees 
as have thinner bark, have from half to a quarter of this allow- 
ance, according to the state of the bark. This deduction is, how- 



OP TIMBER. 309 

ever, a matter of agreement between the buyer and seller, and 
if nothing has been said about it, the purchaser has a right to 
make it at the rate above mentioned. 

Having ascertained or agreed upon the quarter girt of any piece 
of timber, it has to be squared or multiplied by itself, when the 
product is multiplied by the length of the stick in feet, and the 
result divided by 12, and again by 12, or at once by 144 to obtain 
the solidity in cubic feet, provided the quarter girt is taken in 
inches, but if the tree is so large as to permit its girt to be taken 
in feet, this division is unnecessary. 

Example. — What quantity of timber does a tree contain, the 
quarter girt of which is 14j inches, and its length 34 feet? 

14.25x14.25=203.06x34 ft.= 6904.04-i-12=575.33-f-12=47.94 ft. 

If the above had been an oak or elm tree with the bark upon 
it, but still measuring to the same girt, its quarter girt would 
have been called 13j after making the deduction for bark. 

555. In order to avoid the long computations that become ne- 
cessary in measuring large quantities of timber, timber measurers 
are in the constant habit of using Gunter's sliding rule, w^hich 
may be bought at any instrument-maker's, and is the common 
two feet carpenter's rule with a slider applied to one of its sides. 
This part of the rule contains four logarithmic lines of numbers, 
marked at one end by the letters A B C D. The two middle 
lines, B and C, are upon the slider, and the other two upon the 
ruler, but in close contact with the slide, and as the figures or 
numbers on the slide are placed between the two divided lines, 
they serve for both of them. The three lines ABC, are called 
double lines, because the figures from 1 to 10 are contained twice 
in the length of the slide, and the lowest outer line D contains 
only one set of divisions and numbers from 4 to 40, and is called 
the girt line, on account of its great utility in computing the con- 
tents of trees and timber of all forms. 

The other blade of the ruler under the slider is usually filled 
up with tables that are useful in computing quantities of timber 
and its value, so as to render the instrument exceedingly useful 
for all the purposes for which it is intended as comprehended 
under its name, which is the sliding rule for measuring timber. 

The use of the double lines A and B is for working propor- 
tions and finding the areas of plane surfaces; and the use of the 
girt line D, and the other double line C, is for measuring solids. 
The only difficulty the learner will find in using this rule, is the 
correct reading of the divisions; but the method of notation is 
very simple when once understood. To avoid filling the scale 
with figures, every tenth division only has a figure set against it, 



310 ON BUILDING MATERIALS. 

and the intermediate divisions have to be counted. The num- 
bers begin at the left hand, and proceed towards the right; and 
when 1 at the beginning is accounted one, then 1 in the middle 
will be 10, and the 1 at the end 100. But if the first 1 is called 
10, the central 1 will be 100, and that at the extreme end 1000, 
and so on; and of course all the small or intermediate divisions 
must be proportionally varied in reading them off. So soon as 
the mind has become accustomed to this instrument, the speed 
and accuracy with which problems may be solved never fails to 
surprise. With a well divided rule, in skilful hands, a solution 
to about the 200th part of the whole may be relied upon, and 
will be obtained in as short a time as would be necessary to set 
down the figures without working the operation; for in using the 
slide rule no quantities need be set down, and the result is ob- 
tained by inspection, the moment the slider is moved into its 
proper position. Thus, if it was required to work the foregoing 
example by this ruler, all that is necessary is to find that divi- 
sion upon the line C that marks 34 or the length of the tree, and 
to bring that mark opposite 12 on D. Then look for the quar- 
ter girt 14|- on D, and this will stand against 48 on C, agreeing 
very nearly with the result 47. 94 before obtained by figures. 
The slide rule, if not quite as exact as figures, has one decided 
advantage over them, which is, that from the nature and con- 
struction of the instrument, an error cannot occur if the first 
points are set right; while with figures worked in haste, in the 
open air, where timber is constantly measured, the chances of 
error will be very frequent. 

556. The method above described of measuring round timber 
by the square of its quarter girt, is so general among all timber 
measurers, that it would be in vain to attempt any alteration or 
innovation upon the process, notwithstanding it is not a correct 
one; for it gives a result of very nearly one-fourth less than the 
true quantity in the tree, or very nearly what the tree will hold 
after it is trimmed and squared. This has been used as an argu- 
ment by some for continuing this mode of measurement; because 
as it has become a standard rule of practice, the vender is satis- 
fied with it, and the purchaser gets his squared log fit for use 
without the loss that would be attendant upon cutting the slabs 
to waste. The round external pieces, being seldom convertible 
to useful purposes, ought not to be paid for at the same rate as 
the hard square wood in the centre, and this is another reason 
why they should not be fully included in the measurement; but 
in general they will more than pay the cost of sawing off slabs, 
or of hewing, when the chips are valuable as fuel. 

557. The only true rule for finding the contents of tapering 



OF TIMBER. 311 

round timber is that which has been given for finding the solid 
contents of the frustrum of a cone (Prob. XLV. 190); but it is 
too tedious for despatch in business, and is considered too nice for 
the ordinary kinds of timber. As a proof, however, that the rule 
in general use does not give a correct result, we have only to 
consider the three following cases extracted from Dr. Hutton's 
excellent treatise on Mensuration, (8vo. 1802,) in which it will 
be seen that several distinct measurements may be obtained from 
the same tree, all correct according to the rule, and yet all differ- 
ent; while, if the rule was a correct one, the result must be the 
same, by whatever process it may be obtained. 

Example 1. — To cut a piece of round timber in such away 
that the two parts measured separately by the ordinary method 
shall produce a greater solidity than when cut in any other part, 
and greater than if not cut at all. This object will be obtained by 
cutting the tree through, exactly in the middle of its length. 
Thus suppose a tree to girt 14 feet at its large, and 2 feet at its 
small end. Its average girt will then be 8 feet, and if it is 32 
feet long, the whole tree, by the common process, will measure 
to 128 feet; but when cut through in the middle, the thick end 
will measure 121 feet, and the small end 25 feet, whose sum is 
146 feet, being 18 feet more than the entire tree contained. 

Example 2. — To cut a tree so that the greater end may mea- 
sure to the greatest possible quantity. 

Make the cut at that place where the girt is one-third of the 
greater girt. Thus, taking the same tree as in the last example 
32 feet long, and with 14 feet for its greater girt, a line of 4 feet 
8 inches being one-third of the large girt, must be measured off 
and applied round the smaller end of the tree until it fits or be- 
comes the girt; this will take place at about 7 feet from the small 
end, and here the cross cut must be made. The large end or butt 
will now measure 135 J feet, while the whole tree only measured 
to 128 feet. This is a rule that the venders of timber are well 
acquainted with, and often practice, but it is only applicable when 
the greatest girt exceeds three times the least. For when the 
least girt is exactly equal to one-third of the greater, the tree has 
the most advantageous dimensions for measurement, and nothing 
can be cut away without diminishing the quantity. 

Example 3. — To cut a tree so that the part next the greater 
end may measure very nearly the same as the whole tree would 
measure to. 

Call the sum of the girts at the two ends of the whole tree s, 
and their difference d, then multiply d by the sum of d and 4 s, 
and from the root of the product take the difference between d 
and 2 s; then as 2 (^ is to the remainder, so is the whole length 



312 ON BUILDING MATERIALS. 

to the length to be cut off from the small end. Thus using the 
same tree as in the foregoing examples, we shall have ^=16, 
d=l2, and length = 32 feet, and on working the rule it will be 
found that 13.6 feet have to be cut oflf the small end, leaving the 
butt 18.4 feet long. The girt where the cut must take place 
will be found 7.099 feet, and the girt at the large end being 14 
feet, the mean will be very nearly 10.5, one-fourth part of which, 
2.625, will be the quarter girt. Now 2.6252 xl8.4=126. 88 feet, 
being very nearly the same that the whole tree measured to in 
the first example, notwithstanding that one-third part has been 
cut off its length. 

558. The above mentioned anomalies are interesting to, and 
ought to be constantly in the mind of the young engineer or 
builder when purchasing timber, because the small end of a tree 
never measures to much, and may often be useful as a stake or 
post, or even for fire wood, and it is, therefore, better to have 
it delivered than to have it cut off, especially as a larger quantity 
of timber may have to be paid for, after it is separated, than 
before, and the only reason for discarding small ends should be 
bad roads, or difficulty of conveyance, which may make the ad- 
ditional carriage more expensive than the value of the piece of 
timber would compensate for. 

559. Although the preceding is the only rule that timber 
measurers will consent to adopt, yet Dr. Hutton mentions another 
which comes much nearer to the truth. That is to multiply the 
square of one-third of the mean girt by twice the length of the 
tree, when the product will give the true content very nearly. 

560. Another process that has been attempted to be introduced 
in some parts of England, for accurate work, is to divide the 
mean girt by five and square the quotient, which in like manner 
has to be multiplied by twice the length, and this also comes very 
near the truth. 

561. It is frequently necessary to measure timber while it is 
yet standing, and for this purpose a set of divisions is frequently 
engraved on one side of the vertical semicircle e e, Fig. 77, PI. II. 
of the best theodolites, which, if the instrument is set truly level, 
and at a convenient distance from a tree, so that the telescope can 
be moved towards its upper part, will give the height of such 
tree in 100th parts of the horizontal distance of the tree at the 
time of observation. But as all persons who may wish to mea- 
sure timber may not possess a theodolite, and all these instru- 
ments do not contain this set of divisions, other expedients must 
be resorted to; and that which is most used, is to place an upright 
pole in the ground on a level with the root of the tree, and then 
to select a station at which the top of the pole (which is of course 



OF TIMBER. 313 

placed between the tree and the eye) shall appear to coincide 
with that part of the tree to which the measurement is required. 
Then measure the distance of the pole from the tree, and like- 
wise its distance from the place where you stood to make the 
observation, likewise measure the height of the pole and of your 
eye, and having deducted the height of the eye from the height 
of the pole, multiply the remainder by your distance from the 
tree, and divide the product by your distance from the pole. Add 
the height of the eye to the quotient, and the sum will be the true 
height of the tree. 

562. Another and less troublesome method is to provide a 
piece of thin board 10 or 12 inches square, the four sides of 
which must be perfectly straight, equal and at right angles to 
each other. To one corner of this board fix a plumb line of such 
length that its weight may hang about an inch beneath the lower 
corner of the board when it is held in a plane perpendicular to 
the horizon. From the upper angle to which the plumbet is 
attached, draw a strongly marked diagonal line to the opposite 
low corner, or what is still better make a saw cut in this direc- 
tion, or fix a tin pipe about a quarter inch in diameter over such 
line to guide the sight. To use the instrument so prepared, 
select a station upon level ground from which you can see the 
part of the tree you desire to measure to, through the tube or 
saw cut while the plumbet hangs in contact with the vertical side 
of the board, and then on measuring your horizontal distance 
from the tree, and adding the height of the eye from the ground 
thereto, you will obtain the perpendicular height of the tree. 

563. To find the girt of a regularly tapering tree while it is 
standing. First find the height as above directed, and take the 
girt at the bottom. Then, with a short ladder, or at as great a 
height as can be reached, take another girt above the bottom. 
Multiply the difierence between the first and second girts by the 
height of the tree, and divide the product by the distance between 
the girts, and on deducting the quotient from the first girt, the 
girt at the height required will be obtained. 

564. When large timber is squared on its sides, or is cut into 
rectangular pieces by the saw, no difficulty can exist as to its 
mode of measurement, but it must be observed, that the method 
of computing its value depends on the form and thickness of the 
pieces, for all boards are computed by superficial, and all large 
timber by solid or cubical measure. The distinction commences 
at two inches of thickness, therefore every piece of timber that 
measures two inches or upwards on one or both of its sides is 
subject to cubical measure, and of course planks of every descrip- 
tion are included in this denomination. 

40 



314 ON BUILDING MATERIALS. 

565. Boards and planks are always kept assorted, both as to 
length and thickness, and in measuring them it is proper to pre- 
serve this assortment, and to measure all pieces that have the 
same length and thickness together. It saves much time, because 
one dimension as to length and one as to thickness serves for any 
number of pieces, and the surface measure is, therefore, the only 
one that has to be taken. 

Boards of the same length are usually measured across by a 
string, the length of w^hich is determined after the operation is 
finished; but the measuring tape divided into inches is much 
more certain and convenient, as it gives the measure at once. The 
mode of conducting the measurement is to strain the string or 
tape across the width of the board, drawing it forwards with the 
right hand, while it is pinched or held to the edge of the board 
between the finger and thumb of the left hand. The part so held 
is then transferred to the right hand side of a second board, and 
the finger and thum.b of the left hand are then made to slide over 
the tape until its width is determined, and so on for any number 
of boards. The width of each individual board is not noticed or 
set down, as it is only the sum of the whole quantity that is re- 
quired. Fifty or a hundred feet of string or tape, are, therefore, 
frequently run over a lot of boards before any notice is taken of 
the amount; and when the operation is ended, the sum thus ob- 
tained of all the separate widths, is multiplied by the common 
length, and that gives the superficial measure of the whole quantity. 
As before noticed, all boards and planks should be straight and 
square at both their edges, and if they are not so, or if they are 
crooked, or contain such splits or imperfections as might render 
them useless, the purchaser only measures such part as will cut 
to a straight and fair board; and the same rule applies to their 
ends, which are frequently rough, split, and irregular, in which 
cases as much must be deducted from the length as, when cut off, 
will make them square and perfect. 

566. When the value of boards is spoken of, it always refers to 
such as are one inch thick, this being what is technically called 
board measure. Two half inch boards are worth more than a 
single inch board of the same length and breadth, by the cost or 
value of the sawing only; and for the same reason, a two inch 
plank is not quite as valuable as two inch boards, because the 
expense of sawing has not been incurred upon it. Feather edge 
boards, or weather boarding that is one inch thick at one edge, 
and half an inch at the other, is always valued as three-quarter 
boards, and all boards are estimated and sold by the hundred or 
thousand, which of course means 100 or 1000 superficial feet. 

Mahogany and the valuable woods, although sold in the log, 



OP TIMBER. 315 

are always estimated by superficial, or broad measure; so that a 
cubic foot of mahogany would be sold and charged as twelve feet, 
because it would cut into twelve slices, each of which would be 
equal to one superficial foot. And the still more expensive 
woods that are used by turners, and for ornamental purposes, 
such as box-wood, ebony, lignum-vitae, cocoa, ^c, are always 
sold by weight instead of measure. 

567. All the ordinary varieties of timber in pieces exceeding 
two inches square are measured and estimated by cubic measure; 
the method of taking which is so simple and so generally under- 
stood, that it hardly appears necessary to describe it. The super- 
ficial dimensions of the transverse section of the piece must be first 
obtained by multiplying the dimension of one side by that of the 
other at right angles to it, or what is generally called multiply- 
ing the side into the edge, and the product so obtained is again 
multiplied by the length of the piece. If all these dimensions 
are taken in inches, then the product will be the total number of 
cubic inches in the whole piece, and this sum must be divided 
by 1728, (the number of cubic inches in a cube foot,) to reduce 
it to cube feet; but if the area has been taken in inches, and the 
length in feet, which is usually the case, then the product must 
be divided by 12, and the quotient again by 12, or at once by 
144 to procure the necessary reduction. 

All. planks and scantlings of every size are measured in this 
manner, and reduced to cubic feet, adding the price of sawing to 
the cost of the timber, to determine the value. Sawed timber 
either in boards, planks, or scantling, is worth more than the 
mere value of such timber and sawing; because, when a whole 
stick of timber is bought, the purchaser cannot judge of its sound- 
ness throughout, and he takes it on his own risk, as to how it 
will open, as it is technically called. But sawing up a piece of 
timber exposes all its defects and blemishes, if any exist, and the 
buyer of boards or scantling having the right of choice wall of 
course select that only which is free from sap defect and blem- 
ish, and therefore in justice ought to pay a higher price, unless 
he takes a fair proportion of good and bad together. In Eng- 
land the price of timber is almost constantly quoted by the load 
instead of the cube foot, but this does not afiect the calculation, 
since a load is in London and many other places 50 cubic feet, 
but in Bedfordshire and some of the inland counties, 40 feet is 
called a load. The term is therefore vague and uncertain, and 
on this account is not insisted on. In reading English works on 
building or architecture, the price of timber is almost constantly 
given by the load, and if it should be necessary to reduce this to 
cubic feet, the price per load may, without much chance of 



316 ON BUILDING MATERIALS. 

error, be divided by 50, because that is by far the most general 
number of cubic feet considered as a load; and of course revers- 
ing the operation, or mxultiplying the price per foot, will give 
the price per load. 

56S. Sawing is always computed as to its value, and paid for 
by the superficial measure of the surface sawed through, and is 
usually charged by the hundred, meaning the number of hun- 
dred superficial feet that are laid open or exposed by the cuts. 
Wherever water power can be obtained, the sawing is much 
more cheaply and expeditiously performed by the saw mill; but 
where this advantage is not attainable it must be done by the 
hand labour of sawyers, who always w^ork in pairs. The upper 
man who stands on the piece of timber to be cut, is the superior 
workman, because he sets out the lines to be cut, guides the saw 
during the operation, and measures the work when finished; 
while the under man is only required to exert strength for pull- 
ing down the saw. For common timber the saw made use of is 
called a whip saw, and is a mere blade of steel with coarse teeth on 
one of its edges, and a cross handle at each end for the workmen 
to lay hold of. The blade of this saw must be of considerable 
thickness to give it sufficient stiffness and strength for its work; 
and as all saws require their teeth to he set, that is each tooth to 
be forced, in a small degree, out of the plane of the saw, or each 
alternate tooth to be bent, the first towards the one, and the next 
towards the other side of the blade, in order that the teeth may 
cut a wider opening than is necessary for the passage of the blade, 
to prevent its being pinched by the cut already made, which 
would introduce much detrimental friction, so this kind of saw 
wastes a considerable quantity of timber in cutting thin boards, 
and is not applicable to valuable wood; for the cut made is gene- 
rally near one-eighth of an inch wide, consequently, in eight or 
nine cuts, an entire inch board would be wasted by being con- 
verted into saw dust. The more valuable woods are therefore 
cut by a frame saw, which is a much thinner blade, with finer 
teeth, tightly stretched or strained in a light wooden frame, by 
which it is prevented from bending, and the cut made by it 
rarely exceeds the sixteenth or twentieth of an inch in width, so 
that it produces comparatively little waste. Veneers and very 
thin leaves are generally cut by circular saws. The saw in this 
case is a thin circular plate of steel with fine teeth formed on its 
edge, and it is made to revolve on a central shaft, or axle, with 
great velocity, by appropriate machinery. Rough timber is 
usually cut transversely to its length by a long stiff saw, having 
a handle at each end, to which two men apply their strength, and 
the implement is called a cross-cut-saw. In all machine sawing 



OF TIMBER. 317 

the saws move in such directions as are necessary to promote 
the cutting action of their teeth, but never change their places, 
consequently the timber to be cut has to be moved forwards to 
the saw as the cut proceeds, and this constitutes one of the nicest 
points in a good sawing mill that is intended to work on various 
timbers, because the velocity with which the wood moves for- 
wards must be proportioned to its hardness, and the knots and 
inequalities that occur in it, or the saws, will be broken. If the 
same size and quality of timber is constantly used, no such 
adjustment is necessary, because one uniform velocity may 
always be made to suit similar work. In hand-sawing, on the 
contrary, the timber is stationary, and the saw moves forward 
with a speed depending on the exertions of the workmen and the 
hardness of the timber they are dividing. 

569. As all timber is sold by the cube foot, this price of 
course regulates the price of all scantling; consequently if we 
calculate how much of any sized scantling will make a cube foot, 
and add the price of sawing, we shall at once determine the 
value of such scantling. This calculation is simple and easy, but 
it occurs so frequently, and for such a variety of sizes, that the 
following table, in which the quantities are shewn on inspection, 
will be very useful. 



318 



ON BUILDING MATERIALS. 



570. A TABLE shewing what length of timber of any scantling 
from 2 inches to 12 inches square, will make a cube foot of 
timber. 



In. 


/n. 


F^. 


In. 


Zn. 


In. 


Ft. 


7n. 


7n. 


In. 


Fl. 


In. 


2 by 


2 


requires 36 


: 


i 


by 


b\ requires 


6 


^ 


7 


by 7 


requires 2 


: 11 


2 „ 


2^ 


in length 28 


9 


4 


J) 


6 in length 


6 


: 


7 


JJ ''^ 


in length 2 


: 9 


2 „ 


3 


24 





4 


)) 


6i 


5 


• 6 


7 


J, 8 


2 


: 6 


2 „ 


3^ 


20 


7 


4 


;) 


7 


5 


1 


7 


J, 8i 


2 


: 5 


2„ 


4 


18 : 





4 


n 


7J 


4 : 


9 


7 


J, 9 


2 


: 3 


2„ 


4J 


16 





4 


)) 


8 


4 . 


6 


7 


„ H 


2 


: 2 


2„ 


5 


14 : 


5 


4 


)) 


8i 


4 


3 


7 


JJ 10 


2 


: 1 


2„ 


5i 


13 : 


1 


4 


j> 


9 


4 





7 


,j 10^ 


1 


: 11 


2„ 


6 


12 





4 


jj 


9i 


3 : 


9 


7 


,J 11 


1 


: 10 


2 „ 


61 


11 : 


1 


4 


J) 


10 


3 


7 


7 


JJ n^ 


1 


: 9 


2„ 


7 


10 : 


3 


4 


5) 


lOi 


3 : 


5 


7 


J, 12 


1 


: 8 


2„ 


7i 


9 : 


7 


4 


)) 


11 


3 : 


3 










2„ 


8 


9 : 





4 


)> 


lU 


3 : 


2 


8 


,j 8 


2 


: 3 


2" 


8| 


8 : 


6 


4 


>; 


12 


3 : 





8 


JJ 8^ 


2 


: 1 


2 „ 


9 


8 : 















8 


JJ 9 


2 


: 


2. 


9i 


7 : 


7 


5 


}) 


5 


5 : 


9 


8 


J, 9i 




: 10 


2 „ 


10 


7 : 


3 


5 


)} 


5i 


5 : 


3 


8 


,j 10 




: 9 


2„ 


lOi 


6 : 


10 


5 


j> 


6 


4 : 


10 


8 


„ 10^ 




: 8 


2 „ 


11 


6 : 


6 


5 


>j 


6J 


4 : 


5 


8 


JJ 11 




: 7 


2 „ 


lU 


6 : 


4 


5 


>} 


7 


4 : 


1 


8 


,j Hi 




: 7 


2„ 


12 


6 : 





5 
5 




8^^ - 


3 ; 
3 : 


10 

7 


8 


„ 12 




: 6 


3 „ 


3 


16 





5 


JJ 


8i 


3 : 


5 


9 


,j 9 




9 


3„ 


3i 


13 : 


8 


5 


JJ 


9 


3 : 


2 


9 


,j 9i 




: 8 


3 „ 


4 


12 : 





5 


JJ 


9i 


3 : 





9 


,j 10 




: 7 


3„ 


4i 


10 : 


8 


5 


JJ 


10 


2 : 


10 


9 


,j lOi 




6 


3„ 


5 


9 : 


7 


5 


JJ 


10^ 


2 : 


9 


9 


„ 11 




5 


3 „ 


5* 


9 : 





5 


JJ 


11 


2 : 


8 


9 


„ IH 




4 


3„ 


6 


8 : 





5 


JJ 


llj 


2 : 


6 


9 


„ 12 




4 


3„ 


6i 


7 : 


4 


5 


JJ 


12 


2 : 


4 










3 » 


7 


6 : 


10 












10 


,j 10 




5 


2" 


7J 


6 : 


4 


6 


JJ 


6 


4 : 





10 


JJ lOi 




4 


?" 


8 


6 : 





6 


ij 


6^ 


3 : 


8 


10 


JJ 11 




• 4 


2" 


8i 


5 : 


8 


6 


JJ 


7 


3 : 


5 


10 


,j lU 




3 


2» 


9 


5 : 


4 


6 


JJ 


7^ 


3 : 


2 


10 


„ 12 




2 


3„ 


9i 


5 : 





6 


JJ 


8 


3 : 













3" 


10 


4 : 


10 


6 


JJ 


8i 


2 : 


10 


11 


„ 11 




2 


^' 


lOi 


4 : 


6 


6 


JJ 


9 


2 : 


8 


11 


J, Hi 




2 


3„ 


11 


4 : 


4 


6 


JJ 


n 


2 : 


6 


11 


„ 12 




1 


3„ 


llj 


4 : 


2 


6 


JJ 


10 


2 : 


5 










3„ 


12 


4 : 





6 
6 


JJ 
J J 


lOi 
11 


2 : 
2 : 


3 
2 


12 


„ 12 


1 : 





!" 


4 


9 . 





6 


J J 


iH 


2 : 


1 










4 „ 


4i 


8 : 





6 


)) 


12 


2 : 













4„ 


5 


7 : 


2 




If 

















OP TIMBER. 



319 



571. A TABLE for expeditiously measuring round timber, 

(Seep. 554.) 



Quarter 


^rea. 


Quarter 


Area. 


Quarter 


Area. 


girt. 




girt. 




girt. 




Inches. 


Feet. 


Inches. 


Feet. 


Inches. 


Feet. 


6 


0.250 


12 


1.000 


18 


2.250 


6i 


.272 


I2i 


1.042 


18^ 


2.376 


6i 


.294 


12^ 


1.085 


19 


2.506 


6f 


.317 


12| 


1.129 


in 


2.640 


7 


0.340 


13 


1.174 


20 


2.717 


7i 


.364 


13i 


1.219 


20^ 


2.917 


7^ 


.390 


13i 


1.265 


21 


3.062 


7f 


.417 


131 


1.313 


21i 


3.209 


8 


0.444 


14 


1.361 


22 


3.362 


8i 


.472 


14i 


1.410 


22* 


3.516 


Si 


.501 


14^ 


1.460 


23 


3.673 


8f 


.531 


141 


1.511 


23^ 


3.835 


9 


0.562 


15 


1.562 1 


24 


4.0 


9i 


.594 


15i 


1.615 1 


24i 


4.168 


9^ 


.626 


15i 


1.668 


25 


4.340 


91 


.659 


151 


1.722 


25^ 


4.516 


10 


0.694 


16 


1.777 


26 


4.692 


lOi 


.730 


16i 


1.833 


26i 


4.876 


10^ 


.766 


IH 


1.890 


27 


5.062 


lOi 


.803 


m 


1.948 


27i 


5.252 


11 


0.840 


17 


2.006 


28 


5.444 


Hi 


.878 


17i 


2.066 


28i 


5.640 


lU 


.918 


m 


2.126 


29 


5.840 


111 


.950 


171 


2.187 


29i 
30 


5.944 
6.250 



EXAMPLE OF THE USE OF THE ABOVE TABLE. 

Having taken the quarter girt of any piece of timber by mea- 
surement, find the corresponding quarter girt in the table, and 
the number in the column headed '*area" that stands opposite 
being taken out, is to be multiplied by the length of the tree in 
feet, and the product will be the contents in cubic feet and deci- 
mals of a foot. Thus suppose a piece of timber 16 feet 9 inches 
long, (or 16.75 feet,) and its quarter girt to be 20 inches; its 
corresponding area is 2.717, therefore 2.717x16.75=45.50975 
feet the contents. 

Section IV. — Of Iron and other Metals. 

572. Iron and the metals have never been considered as regu- 
lar building materials, but are treated only as auxiliaries to the 



v: 



320 ON BUILDING MATERIALS. 

principal substances that have been ah'eady described; because 
the builder generally uses them merely as means of connecting 
other things together, or adding to their strength in the form of 
nails, screws, bolts, straps, or connecting bars, with the excep- 
tion of the sheet or flattened forms of tin, lead, and copper, 
which have been long used for the occasional covering of roofs, 
or for forming gutters and pipes for the conveyance of rain water 
from the upper parts of buildings, or for the pipes by which 
water is supplied, or is conveyed from one place to another. 
The use of the metals in ordinary buildings is therefore limited. 
But in the constructions of the Engineer, the case is very differ- 
ent. The many places in which iron is now manufactured ren- 
ders it cheap, and easily procured; while the facilities that have 
taken place in its mode of manufacture, and of working it, result- 
ing from its constant employment, have produced an almost entire 
revolution in the works of the Engineer and Millwright, inso- 
much that they now look upon iron almost as their staple com- 
modity, and it is constantly introduced into situations, and ap- 
plied to uses which half a century ago would have been deemed 
preposterous, if not impossible. 

573. The under-ground pipes that supply our cities with 
water were formerly bored out of whole trees, or were formed 
of stone or baked earthenware; the former material was subject 
to such rapid decay as to occasion constant repairs and expense, 
and the latter, being very brittle, was liable to frequent fracture, 
and great difficulty existed in making and maintaining the joints 
water tight, so that no great head or pressure of water could be 
put upon them; but now such pipes are superseded by those of 
cast iron, which seldom need repair, if well laid down in the 
first instance, and they are so durable and strong that no difficulty 
now occurs in sending water to the tops of the highest buildings, 
or drawing it from the bottom of the deepest mines without fear 
of failure or accident. The cog wheels of our mills and ma- 
chines, which a few years ago were made wholly of wood, liable 
to rapid wear and decay, are now constantly made of cast iron 
or other metal, and work with the perfection and precision of 
clock work. The chief members of our steam engines are now 
made wholly of iron; and it is substituted for wood or stone in 
roofs, in floors, in bridges and in rail roads, so that some infor- 
mation on the nature of iron and the other useful metals, and on 
the means of working and appropriating them, becomes quite 
essential and necessary to the Engineer. 

574. Iron is one of the most abundant mineral products of 
nature, but is very rarely met with in the proper metallic state 
in which it is used. All iron when exposed to humid air becomes 



OF IRON. 321 

rusty, or, in the language of chemistry, attracts oxygen from the 
atmosphere, and is converted (at least upon its surface,) into 
oxide of iron, and in process of time will become oxydized 
throughout its whole substance; for the rust of iron is a regular 
oxide, and iron has so strong an affinity for oxygen that it is a 
matter of difficulty to prevent this oxydation going on, notwith- 
standing our desire to avoid it. This at once shows why native 
metallic iron should be scarce, and why most of the ores of that 
metal that are met with should be oxides. The oxides of iron 
seldom present a metallic appearance, and vary in colour from 
bright red to reddish-yellow, or bright yellow, and are occasion- 
ally nearly black; and this metal is so generally disseminated 
over the surface of the globe that these oxides frequently give a 
tint of colour to the whole soil, rendering it brown, yellow or 
red. In these cases the iron exists in such small quantities as to 
render its obtention for useful purposes impossible. What are 
called iron mines are immense collections of the ore of iron form- 
ing in masses that are usually stratified in a nearly horizontal 
direction, and which are frequently from six to twelve or fifteen 
feet in thickness, and of great extent. These mines or forma- 
tions of iron ore are very common, and exist to a greater or less 
extent in all countries, particularly such as are mountainous; but 
the ore is useless without the proximity of a plentiful supply of 
fuel to reduce it, and of limestone, which is necessary for a flux 
to promote the flowing of the metal when produced from its 
original matrix. On this account many valuable deposits of iron 
ore are discovered, but cannot be worked, for iron is now sold at so 
cheap a rate as not to admit the expense of transporting any of 
the necessary constituents for its formation to a distance, and 
those mines only work to great advantage in which the iron ore, 
limestone, and wood or coal are found on the same location, 
which is by no means an uncommon case. 

575. The art of extracting and raising the ore and coal; build- 
ing the furnaces for the reduction and purification of iron; and 
the machinery that is used afterwards for converting it into bars 
and other useful forms, as well as the water-wheels or steam- 
engines by which they are set in motion, are parts of the Civil 
Engineer's business, and the planning and erection of such works 
are a branch of his duty; but as they belong more particularly 
to that division of the profession that embraces mining and metal- 
urgy, they will be passed over for the present; all that is intended 
by the present section, being to put the Engineer in possession 
of such information as will enable him to judge of the qualities 
of iron and the other metals, and to use them with advantage, 
after they are produced, and have reached the public market. 
41 



322 ON BUILDING MATERIALS. 

576. Iron has a strong affinity for most, if not all the natural 
combustibles, and in a hot state will combine readily with them; 
and it also combines or mixes with most of the other metals, 
forming alloys that alter the character of the metal very essen- 
tially. In proof of this, heat a bar of iron in a smith's forge to a 
nearly white, or what blacksmith's call a welding heat, and on 
rubbing it with a stick of brimstone or sulphur, the iron and sul- 
phur will simultaneously melt and fall down in drops, which be- 
come hard on cooling, but on examination will be found to be 
neither iron or sulphur, but a combination of the two, called by 
chemists sulphuret of iron, which is hard and brittle, without 
metallic lustre, and in fact possessing none of those properties 
that render iron valuable. It might be supposed that on heating 
this compound again, the sulphur would be evaporated and driven 
xtff; but this will not be the case. The combination is too strong 
to be dissolved by such means, and the iron is spoiled for all 
ordinary purposes. Iron combined naturally with sulphur, is a 
very common mineral production, found constantly in iron and 
other mines, and known generally by the names of iron or mar- 
tial pyrites, mundic, and marcasite, and it is one of the most 
bright and beautiful minerals, being crystalline with metallic 
lustre, and a colour between brass and gold, so that it has fre- 
quently been supposed by the ignorant to be this latter metal. 
This mineral, when it occurs, must be carefully picked out of the 
iron ore, before it is worked, as a small quantity of it will dete- 
riorate a large quantity of iron. 

577. Carbon, or the pure material of coal, unites with iron in 
the same manner as sulphur, though to a less extent, and is less 
detrimental to it; and as the reduction of iron ore consists in 
tilling a very tall furnace, built for the purpose, with alternate 
layers of iron ore, limestone, and fuel, which soon gets into a 
state of ignition by the fire previously made, and which is urged 
by the most powerful bellows or other blowing machinery, so as 
the iron becomes reduced by being deprived of its oxygen, and 
trickles down through the ignited fuel, it comes into constant 
contact with carbon, while both are at a very high temperature, 
and a union consequently takes place. In this manner, however, 
all iron is reduced in the first instance, and being obtained in a 
fluid or molten state, the bottom of the furnace is tapped, or a 
hole opened into it at stated periods, to permit the fluid iron to 
flow out; and when cold, it first assumes the character of metallic 
iron; but it is unfit for general use, being white and almost crys- 
talline in its fracture when broken, exceedingly brittle, and so 
hard that no file or other tool will touch it. In this state it is 
thick or viscid while hot, and does not flow or run easily, and is 



OF IRON. 323 

therefore unfit for the purposes of the iron founder; but large 
and heavy castings that require to be hard, and have no turning, 
drilling, or other operations of workmanship to be performed 
upon them, are often formed of this iron, which, on its first pro- 
duction, is called crude, or forge iron. 

578. From what has been already stated, it will be evident 
that the fuel used for the reduction of the iron will have consid- 
erable influence upon it. Most kinds of coal contain sulphur, 
which would be so prejudicial to the iron as to prohibit the use 
of that material for the purpose of smelting the ore. Wood, on 
the contrary, contains nothing that can injure iron; but, in its 
ordinary state, its humidity prevents rapid combustion, and it 
will not yield sufficient heat until it has been converted into char- 
coal; and then it is the very best fuel that can be used, but is 
expensive on account of the labour of preparing it, and its very 
rapid combustion. It is believed that Swedish iron, which has 
for many years preserved a higher character for strength, tough- 
ness, and ductility than the metal of any other country, owes its 
perfection to its being manufactured by the charcoal of pine wood; 
and those varieties of iron denominated charcoal iron, from a 
similar process of production, are more sought after for good work 
and command higher prices than other iron. Next to the char- 
coal of wood, mineral charcoal, or the cinders of bituminous coal, 
called coke, is the best fuel for reducing iron ore, or melting iron, 
and this fuel is alone used in Britain, where wood is scarce. It 
has also been introduced into several iron works in this country. 
Coke is pit coal broken into small pieces, ignited with free access 
of air, and permitted to burn until it ceases to give out flame or 
smoke, and the whole mass becomes red hot. It is then shut up 
so that the air cannot reach it, when further combustion becomes 
suspended, and in this state, after being permitted to cool, it is 
ready for use. The making of coke is carried on in a small way, 
by ovens built for the purpose, and which usually contain thirty- 
six bushels of coal. A door serves the common purpose of in- 
troducing the coal and admitting air, and a chimney is built to 
carry off" smoke and promote a circulation of air through the oven 
while the coal is burning, and as soon as the burning has been 
carried to a sufficient extent, the door and chimney are both 
closed, and luted with moist clay, so that no more air can enter, 
and in this state the oven is left some hours for cooling, when 
the coke is drawn out by a large wide iron shovel called a peel, 
which is supported by a chain from a small swinging crane or 
gibbet. Water is thrown on the coke after it is discharged, to 
prevent its rekindling, and it is likewise said to harden and im- 
prove it. After the coke is withdrawn, the oven will retain 



324 ON BUILDING MATERIALS. 

sufficient heat to re-kindle the next charge of ^coals, which is Im- 
mediately introduced, and each charge of 36 bushels generally 
requires 24 hours for its coking, so that the oven may be charged 
daily and kept at constant work. Coke swells so much in its 
formation, that 36 bushels of coal will produce from 45 to 48 
bushels of coke; and when it is good and well burnt it becomes 
very hard, has a shining and almost metallic lustre, and is very 
sonorous. 

Notwithstanding that coke is better and more economically 
made in a close oven than in any other way, yet such ovens are 
too tedious and expensive for large iron works at which the coke 
is constantly made on the open ground. The coal is piled up in 
long heaps, and after being ignited and suffered to burn a suffi- 
cient time, earth is dug and thrown upon them until the air is 
thought to be quite excluded, and the heaps are then watered 
through the earth, and are not opened until the coke becomes 
quite cold. 

579. From the above slight sketch of the manner of produc- 
ing iron, it will appear that it is constantly obtained in a melted 
or fluid state in the first instance; and yet it is obvious that it is 
met with in two distinct forms called bar or Tualleable, and cast 
iron, the characters of which are as yet as distinct as two separate 
metals. Malleable iron is only manufactured into long square 
or rectangular pieces called bars, or long cylinders called rods, 
or flat plates called sheet iron, and if good, it should be charac- 
terized by its toughness, ductility and capability of bending; its 
strength; its power of receiving and retaining a highly reflective 
polish; its fibrous texture; the facility with which it rusts or 
combines with oxygen, by its capability of welding when highly 
heated, so that two pieces may be united by hammering, and 
made as strong as if they had never been separate, (which is one 
of its most valuable properties,) and by its resistance to fusion by 
heat; for malleable iron may be rendered soft and ductile by high 
heat, and may be wholly converted into oxide, and will burn, but 
will not admit of fusion. Cast iron, on the contrary, has no 
ductility and but little toughness, will only admit of bending in 
a slight degree without breaking; is very inferior in strength to 
malleable iron; may be made smooth and polished, but will never 
have a highly reflective surface; has a granular instead of a fibrous 
texture; rusts or combines slowly with oxygen; cannot be united 
by welding: and it fuses and becomes liquid when exposed to a 
high heat. The iron in both cases is the same, and these extra- 
ordinary differences of character appear to depend entirely on the 
quantities of carbon and oxygen that have combined with the 
metal at the time of its reduction. Iron in its malleable state is 



or IRON. 325 

believed to be pure or free from alloy, and the more pure it is, 
the more perfect the metal will be; but cast iron is alloyed 
or mixed with carbon and oxygen, and the different proportions 
of these elements that are present, will sensibly affect the quality 
of the metal. Cast iron is not, therefore, strictly speaking iron, 
but a carburet of iron combined with some oxygen. 

580. The obvious process, therefore, of procuring malleable 
iron, is to refine or purify the imperfect carburet of iron that is 
obtained from the ore by the first process of reduction as above 
described, by taking from it the carbon it had imbibed; and this 
is done by melting the crude or forge iron a second time in a 
reverberating furnace, or one so constructed that the iron shall 
be exposed to a free current of air, and shall be subject to all the 
heat of the fuel, without being in contact with it. So soon as 
the iron is fused, it is kept constantly stirred and moved about 
by iron rods, so as to constantly expose new surfaces to the heat 
and air, which process is called puddling, and by which any car- 
bonaceous matter the iron contained is burnt and consumed, and 
other portions of iron combine with the oxygen of the air; in 
consequence of which changes, the iron shortly looses its fluidity 
and becomes ropy and tenacious like dough, and the workman, 
judging from his experience when this change has been suffi- 
ciently wrought, removes the mass of iron from the furnace, and 
places it on a large anvil where it receives a few blows from a 
very heavy forge hammer worked by machinery, and which 
forms it into the shape of a square bar of from two to three feet 
in length. The blows of this hammer not only form the bar, but 
they render the mass more dense and compact, and drive off all 
the oxide of iron that was formed during the puddling process. 
This flies off in all directions under the hammer, forming scintil- 
lating sparks of great brilliancy and beauty. The short bar while 
yet in a glowing heat is speedily carried to the forming rollers 
(of which Fig. 127, PI. IV., is a representation), and if a square 
bar is desired, it is presented into the square opening d, and is 
carried forward by the revolution of the two cast iron rollers b 
and c. If a smaller bar is required, the hot piece is returned 
back again through the next opening e, and afterwards through 
f, and so on, until it is reduced to the required size. If a round 
rod of iron is required, then the piece is in like manner present- 
ed to and passed through the round openings g h, &c., and thus 
the hot bar which was originally only 30 inches in length, is ex- 
tended to 10 or 12 feet, or even more, and is afterwards cut by 
shears to the required length of the bar. All bars of iron are 
now formed by passing them between rollers of this kind, and 
of course iron mills must possess a number of such rollers suited 



326 ON BUILDING MATERIALS. 

to the sizes and forms of the iron to be produced; because, by 
altering the indentations in the rollers, bar iron of any form may 
be produced, and it is in this way that rail-road iron of particular 
forms is made, or iron mouldings for hand rails and other pur- 
poses. The largest indentations are placed near the ends of the 
rollers, and the smaller ones near their centres, in order to pre- 
serve the strength of the rollers. For the production of sheet 
and hoop iron, the rollers are quite smooth, and without any in- 
dentations; but their general construction is the same in all cases. 
They are supported by two very strong cast iron side frames a 
a, united to a cross piece that is buried in the ground and so fixed 
as to insure the stability of the whole machine. The rollers and 
their necks or gudgeons are turned in a lathe to insure their being 
perfectly cylindrical, and their necks turn in brass bearings to 
diminish friction. The two strong screws i i act upon the tops 
of the brasses of the upper roller, and are for the purpose of 
forcing the two rollers into contact with each other; but in roll- 
ing sheet or hoop iron these screws are relaxed, to permit the 
rollers to separate to a distance equal to the thickness of the 
article to be produced. The two rollers are connected together 
by the two strong cast iron cog wheels k k, to insure their si- 
multaneous motion, and the power of the water-wheel or steam- 
engine that produces their motion is connected to the lower roller 
only. 

581. Before the introduction of rollers into iron mills, bar 
iron was shaped and produced by the blows of the forge hammer 
alone, which occupied considerable time, and did not produce 
bars of the same uniformity as those now manufactured; but there 
is no doubt of the hammering process being the best for the pro- 
duction of good iron. The effect of repeated blows is to con- 
dense the iron and render it more compact and strong, and at the 
same time to effectually drive ofi" all oxide, or carburet of iron 
that may hang about the piece, and which are not so eflfectually 
removed by the equable and steady operation of mere pressure. 
The rollers, however, produce bars with a velocity that is astonish- 
ing to those unaccustomed to the operation, and give them a 
smooth and uniform appearance far superior to what the hammer 
produces, and it is therefore the interest of the manufacturer to 
use rollers, notwithstanding the inferiority of the article, and the 
public, in general, are better pleased to get a handsome looking 
article for a low price, than to pay more for that which is really 
better, but less pleasing to the eye. To compensate for the im- 
perfect operation of the rollers, every bar passed through them 
should be reduced to a small size, and be then cut and doubled; 
a welding heat should then be applied to the two bars, when they 



or IRON. 327 

are again to be passed between the rollers to be consolidated into 
a single bar, and are reduced to the required size. When two 
or more bars are heated, placed together and welded into a single 
bar by the rollers or hammer, the process is called y«^^^e>/^m^, and 
the strength of the iron becomes much improved. Some manu- 
factures give an assurance that all their bars receive this treat- 
ment, which of course enhances the price of the iron, but it is very 
seldom resorted to in rods or round bars, and consequently they 
are considered less trustworthy than those of a square or rectan- 
gular shape. 

582. When malleable or wrought iron, as it is generally call- 
ed, is pure and good, it ought to bear bending even in the cold 
state without breaking; and the fracture when broken should ex- 
hibit a decidedly fibrous character, without much lustre; but if 
the iron is bad or brittle, it will not bear bending without break- 
ing, and the fracture will be brilliant with a granular texture. 
Iron will not draw into a long continuous wire unless it is good 
and pure, and the two varieties may, therefore, be very well ex- 
hibited and illustrated by breaking a piece of large iron wire, and 
a similarly sized cut nail, such as are now generally used. The 
wire must be bent backwards and forwards many times before it 
will give way, while the nail will break by being slightly bent. 
Notwithstanding the qualities of good iron should be always alike, 
yet it is so seldom met with, that three distinctive names have 
been adopted for it, viz: tough iron, and cold short and hot short 
iron. The tough variety (of which good Swedish iron is an 
example), is tough and strong both in the hot and cold state. 
Cold short iron is approved by the smiths because it is easily 
welded and works freely while red hot, but is short or brittle 
when cold. Hot short, on the contrary, will not bear hammer- 
ing while red hot, but is tough and tractable while cold, and is 
therefore useful for forming a number of small articles that do 
not need the aid of fire. 

583. The value of bar iron in the market is generally known 
by the marks or names that are stamped on each bar, indicating 
the manufactory at which it has been produced, and the character 
of which soon becomes known to the trade. But a stranger who 
is unacquainted with these marks or signs cannot select iron with 
any certainty, without breaking the bars and examining the frac- 
ture, in addition to which some of the bars should be heated at 
their ends and struck with a hammer to avoid obtaining hot short' 
iron, which is nearly useless in large w^orks, unless it has to be 
used merely for bars to support weights or strains. 

584. Scrap iron is a variety that is much approved for purposes 
where good iron is required. It derives its name from being 



328 ON BUILDING MATERIALS. 

formed of all the waste scraps and bits of iron that are cut from 
bars or produced in working them, as well as from all old iron 
that is saved. It is sold to the iron mills under the denomina- 
tion of bushel iron, and is there put up into bundles of about 
half a hundred each, and tied and retained in form by hoop iron. 
These bundles being placed in a proper furnace receive a weld- 
ing heat, when they are brought under the forge hammer to weld 
or beat them into a mass and expel the rust or oxide, after which 
they pass through the rollers (like other iron) to be converted 
into bars. The iron being'originally in small pieces, packed in 
all directions, the grain or fibre in this iron is more unequally 
dispersed and interlaced than in any other kind, and it produces 
a very superior bar when the scraps have been of good quality 
and are thoroughly incorporated. 

585. As the conversion of wrought iron to useful purposes is 
never carried on by the Engineer in person, it may seem unne- 
cessary to enter into any details of the manner in which this 
metal is worked; but as he can do very little without recurring 
to iron work, and will constantly have to give orders concerning 
its execution, it is quite necessary that he should know the kind 
of workmen to be employed, the operations which it is their 
business to attend to, and such of the technical phrases as will 
enable him to make his directions clear and intelligible to them, 
and these are therefore briefly given, as follows: 

586. Wrought iron work is performed by two distinct sets of 
workmen, called hlachsmiths and whitesmiths. The blacksmith 
is the first to commence the business, and he works exclusively 
at a fire urged by bellows, and o^dWedi a smithes forge\ he receives 
the iron, and after giving it its due heat in the forge fire, fashions 
it into the required shape by blows of the hammer upon an anvil, 
and certain tools to be used in conjunction with it. If the work 
is so small and light that the smith can blow his own bellows, and 
hold his iron in the left hand while he strikes upon it with a 
hand hammer in his right, he is said to work single handed, and 
the work produced is called single handed work; but in general 
the blacksmith has an assistant called his striker^ who blows the 
bellows, and afterwards strikes upon the hot iron, as soon as it is 
brought upon the anvil, with a heavy sledge hammer, used by 
both hands, and made to swing or revolve over his head in order 
to produce the most powerful blows. The blacksmith all this 
while turns the hot iron into its proper position for receiving the 
blow, uses his hand hammer to assist, as well as to keep time or 
regulate the succession of blows, and occasionally to point out to 
his assistant where he wishes a particular blow to be given, and 
this is continued until the iron becomes so cold that the hammers 



OF IRON. 329 

have little effect upon it, when it is returned to the fire to be 
heated again. Each separate heating is called taking a heat, 
and thus smiths will often say they can do a particular job at a 
single heat, or at two or three heats. When the work is very 
large, the wind from two pair of bellows is frequently carried 
into the same fire, and in this case one striker will not be suffi- 
cient, but two or three are employed, and strike in regular suc- 
cession, when a correct division of time is quite necessary, or 
they might injure each other, as well as the tools they work with. 
The smith's anvil has a beak for turning round or curved work 
upon, and it has a square hole at the opposite end for putting iron 
over to be punched, and for holding the shanks of what are call- 
ed bottom tools, or tools that fit on to the anvil; for if a piece of 
iron has to be rounded or made in the form of a moulding, it is 
done between top and bottom tools. These tools are of steel, 
and carry a concave mould, of the form the iron has to take, made 
in two halves. The bottom tool is inserted in the hole in the 
anvil, the heated iron laid upon it, and the top tool held by a 
long handle, is placed over it and struck by the sledge-hammer 
until the necessary form is given to the iron. Large bars are 
cut by a chisel-edged pair of tools, one of which is a bottom tool, 
and the top tool being placed directly over it, the bar placed 
between them is soon cut. Holes are very expeditiously made 
by punches, which are slightly tapering top tools of various sizes, 
and with blunt ends; the hot iron being laid over the hole in the 
anvil, the punch is held over that hole by its handle, and a few 
blows of the sledge will produce the required hole. Maundrells 
are generally cylindrical tools to be introduced into holes after 
they have been punched, in order to render them truly cylindri- 
cal and of certain size, which is quite necessary when the holes 
have been formed for converting into screws. Maundrells are, 
however, also made square and of various shapes. 

587. One of the most frequent operations of the blacksmith 
is the welding or joining pieces of iron together, which is techni- 
cally called shutting them together, or taking a shut upon them. 
The facility with which this is done adds much to the value of 
wrought iron, and is taken extensive advantage of in many of 
the works of the Engineer; for whenever the length of large bolts 
for fixing a piece of machinery cannot be exactly determined, 
each bolt is finished at its two ends, but sent home in two pieces 
which have to be shut or welded together, when the machinery 
is so far fixed that the necessary length may be ascertained. 
The heads of bolts are put on by forming a collar of square iron, 
which is fitted to the end of the bolt, and is there welded by a 
single heat, but small bolts may be headed by a kind of rivetting 
42 



330 ON BUILDING MATERIALS. 

process, for which purpose the piece of iron is driven into a 
square or cylindrical hole in a block of iron called a swage. 
The hole should be rather too small to admit the hot iron which 
is driven into the swage hole, by a hammer, and is thus made 
truly square or cylindrical, and if properly adjusted as to size, 
will form a head by the action of the ham.mer. The iron con- 
tracts as it cools and can be easily taken out of the swage, 
although it may have been driven into it with great force while 
hot. The swage is the fellow tool to the maundrell, one being 
to give a determinate size to the bolt, and the other to the hole 
the bolt is to pass into when screwed or otherwise finished; and 
as all large machinery is put together with screw bolts and nuts, 
the due fitting of these tools saves much labour afterwards. 

588. Another ordinary operation of the blacksmith is doubling 
and faggotting iron, as before described (581,) but on a smaller 
scale. Whenever a bar of more than ordinary strength is 
required, it is much safer to weld or faggot several bars together 
than to trust to a single one of the same size, more especially as 
large iron is seldom as good and as well wrought throughout its 
whole substance as small bars; for all good iron is rendered bet- 
ter and more tough by long hammering in a hot state, and the 
hammer, unless very heavy, does not produce an effect that is 
felt throughout the thickness of a large bar, as it does in a small 
one. Instead, therefore, of using a single bar of iron three inches 
square, it will be better to faggot or weld together nine inch bars 
to form one of the required size; and in like manner a two inch 
bar may be formed of four inch bars laid together. All nuts for 
screw bolts that are subject to great strain should be formed in 
this manner, by taking iron of the proper width, but of only half 
or one-third of the thickness required, and doubling or tripling 
it with a welding heat, so as to unite the several thicknesses. 
The only thing to be guarded against in shutting and faggotting 
iron is imperfect junction of the parts, owing to a want of suifi- 
cient heat, or to the presence of oxide upon the surfaces that are 
to come together, which will sometimes prevent their union, and 
produce what is called a cold shut or false shut. Such a defect 
may exist without being visible on the outside, and is the cause 
of many shafts, axles, and other parts of machinery breaking; 
but it is a defect that rarely occurs in the workmanship of a good 
and experienced smith, and is always guarded against by bring- 
ing new and clean surfaces into contact, and by sprinkling them 
with dry sand after they have become considerably heated; the 
sand fuses and vitrifies with the heat, and thus protects the sur- 
face of the iron from oxidation by forming a thin coating of glass 



OP IRON. 331 

over it, which is dispelled or driven from the joint by the first 
few blows of the hammer. 

589. Jumping is an operation that is always performed on 
the ends of iron bars that are about to be welded together. It is 
merely making them red hot, and driving them in a longitudinal 
direction against the side of the anvil, or against a block of cast 
iron fixed on the floor, in order to render the ends thicker than 
the rest of the bar; because in welding, the two ends have to be 
beaten together to produce union, consequently the joined part 
of the bar would be less in diameter than any other part, if the 
reduction had not been prevented by previously making the parts 
to be joined so much larger that the necessary hammering 
reduces them to the former dimensions. The joint is then finish- 
ed between a pair of top and bottom tools, and if well made, 
ought not to be perceptible. The great point to be attended to 
in obtaining perfect union is a correct heat, which can only be 
learnt by experience. As a general rule it may be said the heat 
cannot be too great, provided the iron does not burn. This 
burning is in fact conversion into oxide, for if iron is heated 
above a certain extent, it becomes very suddenly oxidized, and 
the then almost fluid iron burns with most beautiful corrusca- 
tions, and is destroyed in its qualities. This excess of heat must 
therefore be carefully avoided, and yet the smith must come as 
near to it as he can with safety. 

590. The fuel of the smith's forge is of great importance, for 
the best iron may be spoiled and rendered incapable of working 
by a bad fire, composed of coals containing sulphur, arsenic, lead, 
or other minerals that will combine with the iron at a high heat, 
and destroy its valuable properties. A small quantity of me- 
tallic lead thrown into a smith's fire will generally make the best 
of iron hot short, or in the smith's language, rotten in the fire, 
so that it will neither weld, or bear hammering without break- 
ing into pieces. Wood charcoal is the safest fuel to use in 
respect to the iron, because it contains nothing that can injure it; 
but it is troublesome in its management to those unaccustomed 
to it, and thr-ows ofi* so many sparks as to make it disagreeable 
to work with it, independent of its burning away very rapidly, 
and requiring the fire to be constantly supplied. Some varieties 
of pit coal make an excellent forge fire, of which the Tanfield- 
moor coal of Northumberland, in England, is an example. It 
is a small and bad coal for household purposes, but so excellent 
on the forge that it is eagerly sought after, even by the black- 
smiths of London and other distant places. 

591. All work produced by the blacksmith is said to be forged, 
and he delivers it in the black or unpolished state in which it 



332 ON BUILDING MATERIALS. 

leaves the fire; this accounts for the name of this class of work- 
men. From the blacksmith it passes to the whitesmith, who 
has nothing to do with the fire, but he files, polishes, and finishes 
the pieces for use; and the perfection of blacksmiths' work is to 
forge so neatly as to bring the pieces very nearly to their intend- 
ed shapes and dimensions, so as to leave the whitesmith little 
more to do than to file away or otherwise remove the black ex- 
ternal surface. In many instances one man goes through both 
operations, but in manufactories, where much is achieved by 
division of labour, it is found most advantageous to keep these 
branches distinct. 

592. The whitesmith works before a vice, which is a strong 
screw press for holding his work firmly and steadily, while under 
his hands, and his tools are cold chisels, saws, tiles, machinery for 
drilling holes in metal, rimers, apparatus for cutting or making 
screws, and a turning lathe. Cold chisels are made wholly of 
steel, and are urged or driven by a hand hammer. They are 
used like the saw, for cutting away portions of iron with greater 
expedition than a file, and they derive their name from their being 
used to cut iron and other metals in the cold state, instead of being 
heated at the forge. Coarse and heavy files succeed for bringing 
the iron under operation, very nearly to its intended size and form, 
and they are followed by finer files and burnishers which remove 
less metal, and produce the necessary smooth surface. Any ne- 
cessary holes that have not been punched by the blacksmith, or 
which may have been too small for his implements, he drills by 
steel drills, which are fixed for use in a strong cranked piece of 
iron called a brace, one end of which carries the drill, and the 
other is pressed upon by a lever and weight, for forcing the drill 
into its work, which is held in the vice, while the brace and drill 
are made to revolve by the hand, or occasionally by the power of 
machinery. Rimers are long tools of hard steel made slightly 
tapering, and with angular sides, and are used for enlarging round 
holes that have been drilled or punched, and for giving a bright 
surface to them. They are placed in the same position as a drill 
in the brace, and are used with it in the manner of a drill. Screws 
are formed by tools constructed for the purpose, and for large 
work they are taps, dies, and a stock or frame, and for small work 
taps and a screw plate. The tap in both cases is a short circular 
rod of the best steel, with a square head for turning it by the 
application of a spanner or screw wrench, which are the names 
applied to those tools by which Engineers and Millwrights turn 
all square headed nuts or screws requiring considerable power. 
The tap is made slightly conical or tapering towards its point, and 
a good and perfect screw or thread is cut upon its surface, when 



OP IRON. 333 

the point and some distance above it, is filed away until this part 
of the tap becomes square, and only carries the screw threads at 
its four angles. The tap is then hardened and tempered in a 
manner that will be explained where steel is described, and is 
ready for use. Being slightly conical, its point is introduced into 
the hole, or nut, in which a hollow or female screw is required, 
and by turning it around by the spanner while the nut is firmly 
held in the vice, the sharp angles will cut away the metal within 
the hole, and produce a concave thread exactly accordant with 
that formed upon the tap, which may be forced into the hole to a 
greater or less extent, as the concave screw is required to be 
larger or less in diameter. The dies are two small blocks of steel 
fitted so as to slide close together, or to a small distance asunder, 
in an iron frame, with two long levers or handles called the stock. 
The steel blocks are brought together by a screw passing through 
one side of the stock, and their two sides that face each other are 
filed out to form a nearly circular hole, in the inside of which a 
screw is cut by the tap before described, so that the impression of 
one half of the screw is in one block, and the other in that which 
is opposed to it, and indentations are filed across the screw threads 
to produce sharp and cutting edges. The bolt to be cut having 
been previously forged into a cylindrical form, is fixed vertically^ 
in the vice, and the part on which the screw is to be cut having 
been introduced between the dies, they are compressed upon it 
by their forcing screw, and made to pinch it tightly, when the 
stock is turned round by its long handles, and a screw thread is 
soon produced upon the bolt. As the cutting proceeds, the move- 
able die is pressed forwards by its screw, until the screw is finish- 
ed, or is cut as deep as required. Each size of screw requires a tap 
and pair of dies proper to itself, but they all fit the same stock, 
so that these tools are alwavs made in sets, and are one of the most 
expensive implements the whitesmith has to use. Small screws 
are not sufficiently deep in their threads to require moveable dies, 
and they are consequently cut by a screw plate, which is a thin 
plate of hardened steel containing a number of holes, each differ- 
ing in diameter, and in each of which a screw has previously been 
cut, so that any cylinder that will pass tightly into any of the 
holes, w^ill be cut or converted into a screw by the turning of the 
plate. The taps are alike for both implements. As an immense 
number of screw bolts and nuts occur in the construction of ma- 
chinery, the formation of them is generally done by piece work 
instead of time. The blacksmith forges bolts and nuts when they 
are all of the same length and thickness, at an agreed price per 
dozen or hundred, and the whitesmith screws them in the same 
manner, subject to the usual agreement that every bolt shall have 



334 ON BUILDING MATERIALS. 

a stipulated quantity of thread upon it, shall be cut home, that is 
shall be worked between the dies until the projecting edges of the 
thread upon the bolt are sharp and smooth, instead of being rough 
and ragged as they will be at first; and that every nut shall be 
free upon its bolt, that is, may be screwed on and otf without the 
exertion of any violence. A washer or flat iron ring, should ac- 
company every bolt; and is put under the nut, not only for orna- 
ment, but it assists in tightening or screwing it up. The operation 
of cutting screws on bolts, and in nuts, is constantly called tapping, 
when performed by the above described tools, and it is so simple, 
requiring strength more than skill, that the whitesmith usually 
transfers it to a labourer. The best and most highly finished 
screws that are used for the adjustment, instead of the putting 
together of machines, are usually produced by chaseing tools in 
the turning lathe, and such screws are said to be chased. Large 
taps, such as before mentioned, should always have their screws 
cut or chased in the lathe. 

593. The last tool to be noticed is the turning lathe, which is 
of first rate importance to the Engineer and mechanic; for without 
its assistance, the perfection that machinery has reached could 
never have been attained, for it alTords the only means the me- 
chanic possesses of rendering materials perfectly round or flat. 
In this machine the thing to be operated upon, is made to revolve 
steadily on an axis, usually in a horizontal position, and the cut- 
ting tool is supported on what is called a rest, in such manner 
that it may remain perfectly steady, or may be made to approach 
or recede from the axis of motion, or can be moved in the direc- 
tion of its length. Every part of the thing to be wrought in a 
lathe will therefore have a correct circular motion round its cen- 
tral axis, and the tool will only cut away or remove such parts 
as project beyond a circle, the radius of which is determined by 
the position of the tool. When such parts have been removed 
the work will be truly circular, and by continuing to press the 
tool inwards towards the axis of the work, its diameter will be 
diminished in any required degree. Spheres, cylinders, cones, 
spheroids, and every other solid tigure that has the circle for its 
base or root, may, therefore, be iormed with the greatest exacti- 
tude by this useful implement; and if the lathe is so strong as to 
resist vibration or tremulous motion, and is equipped with what 
is called a screw-rest, or one in which the cutting tool is held in 
a firm press, and is moved only by the action of fine threaded 
screws, it will work with mathematical precision. By such means 
Mr. Bartonof London, succeeded in diminishing a steel wheel of two 
inches in diameter, by the twenty-two thousandths of an inch, using 
a diamond as the cutting tool. By such tools the pistons of steam- 



OP IRON^ 335 

engines, which require to be truly cylindrical, and nnany other 
parts of nnachinery that require great precision in their dimen- 
sions can alone be produced. The lathe is not confined to wrought 
iron work, but applies equally to cast iron, brass, wood, and in 
fact every thing that can be cut into regular fornns by its opera- 
tion, which is called turnings and it varies in its dimensions from 
lathes capable of carrying pieces of several tons in weight, down 
to the small implement upon which the watchmaker forms his 
finest wheels and pivots. The method of communicating motion 
to the work, must of course vary according to its weight and mag- 
nitude; thus the maker of large steam-engines and machines drives 
his lathes by the power of steam or water-wheels, while smaller 
concerns are satisfied with the power of a horse or man. The 
generality of lathes for common purposes, are turned by one foot 
of the workman acting upon a treadle; and the watchmaker 
moves his work with a single horse hair strained by a light cane 
bow that is worked by the left hand, while his right holds the 
cutting tool. The moving velocity of all lathes should be variable, 
if they are intended for various materials, because cast iion re- 
quires a very slow motion; iron and steel one rather more rapid; 
brass a great velocity, and wood one that is more moderate. 
Lathes are not only used for the ordinary purposes of turning, but 
likewise for drilling holes, boring cylinders, chasing screws, and 
many other useful purposes. The diameter of work while pro- 
ceeding in the lathe, is measured by compasses with curved legs, 
called calliper compasses, and if the calliper compasses have 
straight legs in one piece, with the curved ones projecting beyond 
the joint or pivot, like wholes and halves, (95,) but of the same 
radius as the curved points, then such compasses become in and 
out callipers. Each pair of points will be at the same distance 
at every opening, therefore by such an instrument a hollow cylin- 
der may be formed that will exactly tit a convex one, without the 
trouble of trying them together. 

594. Soldering is a process constantly resorted to by workers 
in metal, for the purpose of permanently uniting similar or dis- 
similar metals, so that they can only be separated again by frac- 
ture or exposure to as great a heat as was at first used to pro- 
duce their union. It depends on the principle of different metals 
requiring different temperatures for their fusion, and on compound 
metals or alloys fusing more readily than simple ones. A solder 
must, therefore, in every case, be more fusible than the metal to 
which it is applied, and yet by using the solder with a flux that 
promotes the fusion of both, such an incorporation takes place as 
unites both firmly together. Solders are divided into two kinds, 
called soft and hard; and soft solder includes every composition 



336 ON BUILDING MATERIALS. 

that can be applied and will take effect below a red or visible 
heat; while for hard soldering the metals to be attached, as well 
as the solder, must be red hot before the union can be effected. 
Every joint, therefore, that has to resist great heat, must be hard 
soldered, and soft solder can only be applied to such things as will 
never be heated above 550°. Tin and lead occasionally mixed 
with small quantities of silver or copper, constitute the materials 
of soft solder, while hard solder is very fine yellow brass, contain- 
ing an excess of zinc, reduced to a fine granular state for applica- 
tion, when it is called spelter. The fluxes used with soft solder, 
are powdered rosin for tin, copper and iron; tallow for lead, and 
muriate of ammonia, dissolved in water, for brass. For hard sol- 
dering brass and cast iron, muriate of ammonia is frequently used; 
but the salt called borax, (biborate of soda), is the ingredient most 
frequently resorted to, and is the only one that answers perfectly 
for hard soldering iron, steel and copper. As hard soldering is 
constantly effected by brass, it is more frequently called brazing 
than soldering, which last term is constantly applied to all soft 
soldering operations. The soldering that the whitesmith has to 
perform, is almost constantly brazing, to effect which the parts 
of the iron to be joined are made to fit each other, and if neces- 
sary, are tied and bound together by small soft iron wire, called 
binding wire. The powdered spelter and borax are applied upon 
the intended joint, and the work is held by a pair of tongs over a 
charcoal fire in a small forge for the purpose. The heat is raised 
by the bellows, and the work watched, that the process may not 
go too far, and as a red heat comes on, the spelter and borax will 
fuze and run into the joint, which must be instantly moved from 
the fire, and when cold, the binding wires are taken off, and the 
inequalities of the joint made smooth by the file. 

595. The several processes and operations to which wrought 
iron is submitted to produce its different forms, are all included 
in what has been above described, with the exception of mere 
details, which belong alone to the workman, and cannot be inter- 
esting to the Engineer. Indeed the processes that have been enu- 
merated, would not have been extended to such a length if it was 
not necessary that the Engineer should be acquainted at least with 
their existence; and as they will all have to be referred to again 
in future parts of this work, it was thought better to describe the 
whole of them at once in this place, than to detach what must 
have been said upon them. Wrought iron work, whether black 
or bright, is always charged and estimated by weight. 

We shall now proceed to point out the nature and treatment 



OF CAST IRON. 337 



596. Of Cast Iron, 

Which, on account of its hardness, strength, durability, and 
small tendency to oxydation, its resistance ot" heat and cold, and 
the facility with which it may be put into any form, at a small 
expense, renders it by far the most valuable and important mate- 
rial that the Engineer has control over. 

A general account has already been given of the first produc- 
tion or reduction, as it is called, of iron from its ore, (577,) and 
of the kind of metal produced, which, owing to its being very hard, 
viscid, and incapable of flowing freely, is untit for making castings 
in iron. The first running of the iron as there stated is called 
crude ov forge iVo72, because it has not been refined, but is in a 
proper state for the forge, or mill, where it is converted into bar 
iron, for which it is well suited, as containing very little carbon. 
Now, iron for casting, or foundry iron as it is called, becomes good 
and soft in proportion as it receives a higher charge of carbon, con- 
sequently, a completely opposite process must be used to obtain 
this iron and bar iron; the one having to be charged with carbon, 
while the other has to be deprived of it. Accordingly instead of 
remelting the forge iron in a furnace where it is exposed to air 
and heat only, without contact with the fuel, as is done to make 
bar iron; it must be remelted for making foundry iron in close 
mixture wdth the fuel, and w^ith as little exposure to air as possi- 
ble; and it accordingly undergoes this melting in which it absorbs 
an additional quantity of carbon, after which it is tapped and cast 
into foundry pigs. The name of pig iron is very generally applied 
in all countries to those straight bars of about four feet in length 
in which iron for casting is sold. The iron, when it first runs from 
the furnace, is received into a round bottomed trough or gutter 
made in sand, from one side of which a number of similar troughs 
are form.ed at right angles to the first, and three or four inches 
apart, the whole being truly level, and open to common commu- 
nication, so that when the first or principal gutter fills with fluid 
iron, all the others \y\\\ fill also, and the quantity of iron when so 
cast and taken up, resembles an immense comb with coarse teeth. 
These teeth are knocked otTclose to their junction with the trans- 
verse piece, and tiien become pigs of iron; while the cross piece, 
which is always larger and more irregular than the others, is 
called the sow. Pig and sow iron are always sold together; but 
the sow often contains impurities on the furnace, and is not so much 
esteemed as the pigs. 

597. It was stated, as a general principle, that the first reduc- 
tion of iron ore produces crude or forge iron, but there are excep- 
43 



338 ON BUILDING MATERIALS. 

tions arising from the quality of the ore, the nature of the fuel, 
and the management of the furnace, by which foundry pigs of 
good quahty are produced in the first instance, and thus the loss 
of time and fuel attendant upon a second melting is avoided. 

598. The making of iron castings constitutes a distinct branch 
of business, and is carried on by the iron founder in a manufactory 
called an iron foundry; and the utility of cast iron is now so uni- 
versally established that few large towns are without such an 
establishment. It is a business seldom personally attended to by 
the Civil Engineer; therefore no specific directions need be given 
for carrying it on. But every Engineer should be acquainted with 
the operations carried on in the foundry, and with the manner of 
making moulds; because he will constantly have to correspond 
with foundries, and to send orders to them, and if he does not 
possess this knowledge, he will frequently incur great expense in 
preparing patterns for castings that may be useless, or he may 
require articles to be made that cannot be executed; but the ex- 
planations that follow, it is presumed, will prevent his running 
into these, or other difficulties. 

599. In order to save the expense of transporting, and remelt- 
ing large quantities of iron, very heavy castings are most fre- 
quently made at the iron works, where the iron is produced. Such 
is the case with the castings for large iron bridges, or the plates 
for rail-roads. But these large concerns will not be troubled with 
small orders, and they consequently devolve upon the iron founder, 
who is very seldom an iron maker, but has to buy his pig iron at 
the common public market, where it varies in price according to 
the demand and quantity manufactured. The founder therefore 
works entirely with new pig iron or with old metal, such as old or 
broken cast iron articles, which he buys for less than half the price 
of new metal, and melts over again, generally in conjunction with 
new metal. 

600. Pig iron is known in the market under three denomina- 
tions, called No. 1, 2 and 3. No. 1, also called soft grey cast iron, 
is the best quality. No. 2, a medium kind, and No. 3 is hard and 
white, and very little better than forge iron. The founder judges 
of it chiefly by the appearance of its fracture, by its sound, and 
by seeing if it indents or gives way, or breaks before the blows 
of a hammer. Pigs are usually tried by placing one upon the 
ground, and then throwing those that have to be examined trans- 
versely across it, and the ease or facility with which they break 
will afford a very fair criterion of the strength or toughness of 
the iron. The sound of the blow must at the same time be at- 
tended to, for the finest soft iron scarcely yields any sound, except 
that of the blow; it falls dead upon the block like a bar of lead, 



OF CAST IRON. 339 

and its fracture will be coarsely granular, with no great lustre, 
but much resembling coarse grained black-lead. A No. 3 pig, on 
the contrary, being very brittle, breaks with a slight blow, and 
rebounds from the block with a ringing metallic sound, and its 
fracture will be of silvery whiteness, with strong metallic lustre, 
and little or no granular appearance, while J\o. 2 should be a 
medium between the two, and without much lustre. The shape 
of the pig must be regarded among the other qualities in selecting 
iron, for if the top surface is clean and smooth, and the under 
side carries a good impression of all the little inequalities of the 
sand in which it has been cast, this is proof that the iron is fiee 
as it is called, i. e. will flow well into the mould when it is cast; 
but if its impressions are obtuse, or it has not filled out all the pig 
mould, and carries much dross or scoria on its back, it denotes 
sluggish iron, or such as is viscid, and will not flow freely. These 
varieties of iron bear prices proportioned to their goodness, and 
No. 1 is frequently twice the value of No. 3. They have their 
advantages in particular kinds of work; thus, if a piece of cast iron 
has to be turned, or filed, and has many holes to be drilled into it, 
and these perhaps tapped for screws, it should be cast from the 
purest No. 1 iron. If the piece when cast, has but little work to 
be done to it, but is to be used as it leaves the mould, and great 
strength is required. No. 2 iron should be selected; and if the piece 
has to give or receive repeated hard blows, and has no work to be 
performed upon it, as in a cast iron head or anvil, or the ram of 
a pile driving engine, or the shoes of a stamping mill, then No. 3 
iron will be the best on account of its hardness. The Engineer 
knowing these qualities, will order his castings to be made from 
that metal which he knows will answer his purpose best, while 
the founder constantly uses the iron ordered for the sake of his 
reputation, and charges according to its quality, and the difficulty 
of executing the work. 

601. The several varieties of pig iron above enumerated, ap- 
pear to derive their character from the quantity of carbon with 
which they have combined at the time of their formation; thus, 
No. I iron contains the largest quantity, so large indeed that an 
artificial carburet of iron resembling black-lead, is frequently seen 
to float on the surface of the pigs, while the metal is running into 
them from the furnace, and as they cool this substance runs into 
minute and highly resplendent crystals, which are found in cavi- 
ties on the surface and in the interstices in the inside of the pig, 
and is denominated by the iron makers kish. The experienced 
iron founder desires no better proof of the softness and goodness 
of No. 1 iron than finding that it breaks with a kishey fracture. 
No. 2 iron of course contains less carbon, and No. 3 is scarcely 
removed in this respect from crude or forge iron. 



340 ON BUILDING MATERIALS. 

602. The iron founcler uses two distinct kinds of furnace for 
melting his iron, called a cupola and an air furnace; but small 
foundries seldom have more than one, or at most two cupolas. 
The cupola will only melt from 1 to 10 cwt. of metal at once, and 
during the whole of its operation requires to be urged by a very 
large and powerful pair of bellows, or other blowing machine; 
while the wind or air furnace should never be used to fuse less 
than one ton of iron, and is made large enough to melt from five 
to seven tons at once, and requires no artificial blowing, but works 
by a natural current of air induced by a very tall chimney: and 
as the fuel of the cupola is coke or charcoal, and it requires the 
power of two men, or their equivalent in machiner}^ to work the 
bellows, and the air furnace works with well selected but raw pit 
coal, free from sulphur, so of course its operation is much more 
economical, and it gives the large founder who has sufficient work 
to keep it in constant action, a decided advantage on the score of 
profit. 

603. The weight of every large casting that has to be made, 
is calculated before the metal is melted to make it, and from 15 
to 20 per cent, more metal is put into the furnace than will be 
necessary for it; because if a large casting should be spoiled for 
want of sufficient metal to fill up the mould, the loss of fuel and 
labour w^ould be very considerable; and a sufficient number of 
small moulds are constantly in readiness to consume the extra 
quantity that may be left. The method of making this calcula- 
tion is given hereafter (631 and 632). 

604. There are four denominations of castings among iron 
founders, depending upon the manner in which the mould is made. 
They are open sand; tlask or box castings; in green sand; dry sand; 
and loam castings: and asdifferent degrees of trouble and risk attend 
them, they generally increase in price in the order above men- 
tioned, exclusive of the value of the iron used in their formation. 
The moulds for all of them, with the exception of the last, are 
made with sand, but it is sand of peculiar properties, and is diffi- 
cult to procure in some places, for it should be perfectly homo- 
geneous, and its grains as equal sized as possible, and it must con- 
tain sufficient loamy or clayey matter to cause it to maintain any 
particular form that is given to it when slightly moistened, and it 
must not coke or burn into a kind of brick from the heat of the 
melted iron, nor be so close and compact as to prevent the escape 
of steam and rarified air which are rapidly generated when the 
hot iron is poured into the mould. Good moulding sand is, there- 
fore, a great desideratum with the iron founder, and is on this 
account often transported many miles. 

G05. Open sand casting is only applicable to flat plates or bars 



OP CAST IRON. 341 

in which it is not detrimental to have one side rough and uneven. 
They are made by spreading a sufficient quantity of moulding 
sand, sufficiently moistened to give it tenacity, upon the floor of 
the foundry, which spreading is always effected by passing it 
through a fine wire sieve, and then making its surface (if a flat 
plate has to be cast) perfectly hard and level, which is done by a 
light flat faced iron rammer with a long handle, and repeated 
applications of a small level like that shewn at Fig. 84, PI. III., 
tried upon the surface in all directions. When the surface is thus 
rendered hard and level, it is made smooth and almost polished by 
being rubbed over with a small trowel, similar in shape to the 
floating trowel of a plasterer. That done, the walls that are to 
confine the iron, and give a particular form to the plate, whether 
it be square, circular, or of any other shape, are built; and for 
this purpose smooth strips of wood of the same thickness that the 
plate is to have, and having the same contour on their edges with 
itself, or the same mouldings or ornaments, are laid down upon 
the flat surface in positions exactly accordant with the intended 
edges of the plate, and some of the external sand is gathered by 
the hand and pressed closely against these strips, and rammed 
close to them by a hand rammer, after which all superfluous sand 
is cut away by passing a trowel over the tops of the strips in a 
horizontal direction, when the strips are taken up, and a perfect 
concave representation of the plate to be cast will be left in the 
sand. If a name, letters, or ornaments in relief are required on 
the face of the plate, they may now be stamped or indented on 
the smooth surface of the sand, and the mould will be readv for 

' ml 

receiving the metal. 

606. The moulders and the furnace men, are a distinct set of 
workmen in a foundry, and while the former are employed in 
making their moulds, the latter are engaged in meltinij the metal, 
and as soon as it is in a fit state for running, the furnace man 
gives notice to the moulders that he is about to fa^o, that is to say, 
to knock open by means of an iron crow bar and a sledge ham- 
mer, a hole made purposely in the bottom of the furnace, but 
which during the melting of the iron had been stopped by clay 
and sand, which becomes exceedingly hard from the heat of the 
inclosed melted iron. When this hole is open the whole charge 
of iron that has been melted runs out; therefore, previously to 
opening it, the moulders place a large iron bowl lined with loam, 
and called a shank, before the tap hole to receive the iron. The 
shank has a long single iron handle in front, and a forked or double 
handle behind, so that it can be carried either by two or by three 
men, according to its weight, and in this the melted metal is car- 
ried to the moulds which are filled, and as the moulders should 



f 
342 ON BUILDING MATERIALS. 

use the precaution of keeping a number of small moulds in pre- 
paration, so if this is done, the shank is carried from one to the 
other,and not an ounce of the melted metalneed be wasted. This is 
a necessary precaution to insure profit to a foundry, the chief ex- 
pense of which is the fuel necessary to melt the iron, and if unused 
metal remains in the shank, it must be discharged upon the floor 
to be melted over again, with a certain loss that iron sustains at 
every fusion by a portion of it being converted into useless oxide. 

607. But to return to the open sand plate, this only requires the 
melted metal to be poured into the mould for its completion. If 
the mould is not quite filled with metal, the plate may be thinner 
than was intended, but it never can be thicker, because the walls 
were regulated in height by the strips made use of for their for- 
mation, and which were equal in thickness to the intended plate; 
consequently, if too much metal is poured into the mould, it w-ill flow 
over the walls and run to w^aste; and if the sand bottom has been 
correctly levelled, we may be sure that the two sides of the plate 
will be parallel, because the upper unconfined surface of the fluid 
iron will be truly level. The instant the iron sets or becomes 
hard, a covering of three or four inches in thickness of dry sand 
should be thrown by a shovel over every open sand casting to 
prevent exposure to the air and sudden cooling which would warp 
or bend the plate, or perhaps cause it to crack. It is a matter of 
importance in all recent castings to prevent partial cooling, and 
the irregular contraction that would follow it. All metals expand 
by heat and contract on cooling; and iron in its melted state is in 
its greatest state of expansion, but contraction follows rapidly, and 
as the metal in contact with the mould chills and sets very 
speedily, so contraction takes place on that side, while the upper 
part of the metal may be yet fluid and highly expanded. Cover- 
ing the top of the casting with sand, puts it therefore in the same 
state as the bottom, and as sand is a very bad conductor of heat, 
a more equal and gradual cooling is produced, and an equable 
contraction follows. 

G08. Open sand casting is not confined to mere parallel plates, 
but is applicable to every solid figure that will admit its upper 
surface, (which must be flat,) to lie in a horizontal position. 
Thus the fire bars of steam-engine boilers and other furnaces re- 
quire neither beauty or perfection of workmanship, and these are, 
therefore, very commonly cast in open sand. But to produce 
these what is called a pattern is necessary. The pattern is a fac 
simile of the thing to be produced, but is made of wood instead of 
iron, and its use is to make the impression in the sand, which the 
melted iron is intended to occupy after the pattern has been with- 
drawn. The pattern is therefore imbedded in the sand, which is 



OF CAST IRON. 343 

closely rammed around it, taking care to keep the top of the pat- 
tern perfectly level. When moulded, the pattern is gently and 
carefully withdrawn in a vertical direction from the sand, and 
may be used to make another mould or impression, because one 
pattern will produce any number of castings, all of which must be 
perfectly similar. Even a three or four sided solid pyramid may 
be cast by the open sand process, provided its point be placed 
downwards and its base upwards, of even if one of its sides is 
upwards and placed horizontally. 

609. The disadvantage of open sand castings, is their liability 
to warp or change their flat form if they are large and extended, 
and great care is not taken to insure slow and equable cooling; 
and that their upper side will always be full of air bubbles, blis- 

» ters, and portions of dross or oxide, that will float on the metal 
and render it rough and unsightly, but the under side that was 
next the sand, will be as perfect as castings produced in any other 
"way. Such castings can therefore only be used for flooring plates, 
backs of fire places, or in positions where one side only is exposed 
to view, or for plates that are used within walls or in hidden posi- 
tions, where strength without beauty is required. The advan- 
tages of this sort of casting are, the ease and expedition with 
which it is made, which renders its price lower than other work, 
and that in many cases no pattern is necessary, except a thin 
board cut to the contour of the plate to be produced if it is ir- 
regular, and which is called a template^ or about a foot of a circle 
with a wooden radius, if a circular plate is wanted, which is called 
a sweep. Square or rectangular plates require no preparation, as 
straight edges are kept in every foundry. 

610. When every side of a casting requires to be fair and 
smooth, the top of the mould must be covered with sand as well 
as the other parts, and this can only be eflTected by making the 
mould in a box that divides into two or more parts, according to 
the intricacy of the body to be formed, and such boxes make a 
part of the implements of every foundry, and are called Jl.asks. 
All flask castings require a model or pattern, and if the box is 
filled with the ordinary damp sand of the foundry, without drying 
or other preparation, such sand is called green or fresh sand, and 
the casting produced is called a box or flask casting, or sometimes 
a flask casting in green sand. The boxes or flasks are frequently 
made of plank, especially for temporary purposes, but as wood is 
very liable to be burnt by the heat of melted iron, or at any rate 
to crack and warp, old established foundries have their flasks of 
cast iron, when they are very durable with proper care. Flasks 
are made of various sizes and forms suitable to the moulds they 
have to contain, and one advantage attending cast iron flasks is 



344 ON BUILDING MATERIALS. 

that by having a few side and end plates of various lengths, put 
together with screw bolts and nuts at the angles, one pair of sides 
or ends may be substituted for another, provided the bolt holes are 
made to correspond, and thus a pair of flasks may be altered from 
one form to another to suit any work that has to be done. Fig. 130, 
PI. IV., represents a pair of long narrow flasks suitable for casting 
straight iron pipes. They consist each of four plates, forming two 
boxcsyand g, of exactly the same dimensions, and are without 
tops or bottoms; hut to prevent the long sides from bulging when 
the box is filled with rammed sand, a sufficient number of cross 
braces hh must be fixed across the top of the upper box f, and 
the lower side of the box g; the two sides that come into contact 
being left quite open and unincumbered. The lower edge of the 
upper box, and the upper edge of the lower one, must be even 
and smooth, to insure their making a good joint, or fitting without 
the possibility of moving when placed together, and their exact 
position is preserved by iron steadying pins fixed in the projections 
m m, called lugs, and passing into holes in similar projections / / 
on the upper edge of the lower box. Similar projections and pins 
are placed on the other side of the boxes, so that the upper box 
may be lifted from the lower one by its handles i i, and can be 
replaced again with the certainty of being in precisely the same 
position. To make a casting, a pattern is necessary, and if a pipe 
with flanches or flat circular plates at its ends for making a screw 
bolt joint is to be produced, the form of the pattern will be such 
as is shewn at Fig. 132. The two flanches x x, have the size, 
form, and appearance that the real flanches are to have when 
cast, but the body of the pipe d w, is a solid piece of wood, turned 
in the lathe, and the whole must be very smooth and well polish- 
ed, for the good and smooth appearance of the casting always 
depends upon the perfection and finishing of the pattern. To 
mould this pattern, the top boxy is removed, and the bottom one 
g is placed in a nearly level position, on the floor of the foundry 
(which is always formed of moulding sand) which makes a close 
bottom for it. The lower box is then filled with moulding sand, 
which is rammed into it by small rammers of iron, until it attains 
such a height that the pattern placed in the box may be supported 
on the two edges x x o^ the flanches, at such a height that the 
central line zvv w o[ the pattern will be even with the top of the 
box, or in other words, until one half of the pattern is sunk into 
the box, and the other half is wholly above its top edge. The 
lower box is then filled up level with its top, with moist sand, care- 
fully rarnmed around the pattern, so as to insure the obtaining a 
perfect impression of its lower half in the sand of the lower box, 
when the top of the sand is made as hard, level, and smooth as 



OF CAST IRON. 345 

possible by the moulder's well polished trowel. That done, a 
small quantity of perfectly dry sand, or tine Flanders' brick dust, 
is sprinkled over the sand, and is called parting sand, its object being 
to prevent the sand about to be placed in the upper box from ad- 
hering to that already deposited. The top box is now placed upon 
the bottom one, as shewn in the figure, when it is in like manner 
filled with well rammed moulding sand, for obtaining the impres- 
sion of the upper half of the pattern. Before filling the top box, 
two slightly tapering turned sticks are placed vertically upon the 
top of the pattern, and are rammed about with sand as well as the 
pattern, and when the upper box is quite filled, the moulding will 
be completed. A funnel shaped cavity is sunk by the fingers in 
the top of the sand round one of the taper sticks, and they are 
then withdrawn from the sand, by twisting them round and draw- 
ing them upwards at the same time, when of course two corres- 
ponding holes reaching to the pattern will be left. The one that 
has been made funnel-shaped is called the gate, and is intended 
for the channel by which the melted iron is to be poured into the 
mould, and the other is called the vent, because it is for the escape 
of the air contained in the mould when the iron is introduced, as 
well as the steam and gas that is generated as soon as the hot iron 
reaches the damp sand; and it answers another important purpose, 
that of informing the moulder when the iron is up, or in other words 
when the mould is full, and he may cease pouring; because the 
fluid iron will not rise up the vent in attaining its level until the 
mould is quite full. Having finished the moulding as described, 
one of the most delicate and troublesome operations of the moulder 
follows; that is, separating the two boxes for the removal of the 
pattern without breaking down any of the sand in which the im- 
pression has been formed. To effect this, a workman goes to each 
top handle, i i, and they raise the top box vertically and as steadily 
and carefully as possible, when the pattern remains fixed in the 
bottom box, and in general a correct and perfect impression of 
the upper half will be found in the top box, which is now invert- 
ed or placed on one of its sides upon the floor for the purpose of 
its examination and repair, if necessary. It very frequently hap- 
pens that portions of the top sand will hang about or adhere to the 
pattern, and if so, they require to be carefully taken up, and re- 
stored to their proper places in the top box, where they are made 
to adhere by the pressure of a small trowel, and in this way the 
top impression is made as smooth and perfect as possible. The 
pattern has now to be removed from the bottom box, which is in 
general an easy operation. A little water from a wet rag or 
sponge is applied all round the pattern, to render the sand more 
compact, and one or two nails are driven into the top of the pat- 
44 



346 ON BUILDING MATERIALS. 

tern to make handles for lifting it; or it is gently struck with a 
hamnner to loosen it in the sand, when there will be little difficulty 
in raising it gently and carefully from its bed, without much 
breaking or damage to the sand; but if any happens, it is always 
repaired and rendered smooth; and then the top box is restored to 
its former place upon the bottom one, and a perfect concave re- 
presentation of the pattern will of course exist ready to receive 
the metal. 

611. If metal should now be poured into this mould, it would 
evidently produce a solid mass shaped like the pattern, but no 
pipe; because the bore or hollow cavity has not been provided 
for. It is impossible in most cases to produce a clean or well 
shaped and defined hole in castings by the pattern alone; because 
if a hole is made in a pattern, the plug of sand that will be ram- 
med into it in moulding, will constantly break off and remain in 
the pattern, unless the hole is very tapering or conical. The 
founder, therefore, whenever he desires to produce holes in his 
castings, either for the passage of screw bolts, the bores of pipes, 
or any other purpose, has recourse to what are called cores, and a 
knowledge of the management and application of cores is of more 
importance to the Civil Engineer than almost any other part of 
the foundry business. 

612. One way in which an Engineer transacts business with a 
distant foundry, is for him to make very complete and detailed 
drawings, indicating every hole, cavity and other particular that 
he wishes to appear in the desired casting, and to order the iron 
founder to make patterns in accordance with such drawings. 
Pattern-makers who perfectly understand the nature of this busi- 
ness, therefore usually form part of the establishment of every 
large foundry. This method, although often resorted to, is by no 
means the best. Making such drawings as are necessary, occa- 
sions loss of time and great trouble to the Engineer. Loss of time 
frequently occurs again at the foundry from their pattern-makers 
being previously occupied on other business, and patterns so made 
are generally charged at very high prices, and what is worse than 
all, the drawing is frequently misunderstood, and a casting sent 
home that does not agree with what is wanted. The most usual 
and convenient proceeding is, therefore, for the Engineer, who re- 
quires many castings, to have a workman in his employ that is 
capable of making patterns. He works in that case from oral 
description, without a troublesome drawing; the pattern is made 
under the eye or directions of the Engineer, he tries its dimen- 
sions, or even puts it into the place the iron is to occupy, it is made 
at the time it is wanted, and when sent to the foundry it is soon 
cast, and there is a perfect confidence that the metal when re- 



OP CAST IRON. 347 

ceived will answer the purpose for which it is intended. Still, if 
the Engineer or pattern-nnaker does not know how to make the 
necessary preparations for hollows, holes, and cavities, he will 
probably receive a solid casting, when he expects a hollow one, 
or may have the trouble and expense of drilling holes which might 
have been produced without charge by the founder; and cast iron 
is so hard and refractory a material to work in, that every pre- 
caution should be used to insure having as little work as possible 
to do upon a piece of cast work after it leaves the foundry. 

613. Patterns in most respects are perfect representations of 
the thing to be cast, but the holes that are required are just the 
reverse, for instead of making a hole in the pattern where a hole 
is desired in the casting, holes in patterns are almost constantly 
marked by convex projections of the size and shape of the hole, 
and such projections are called prints. The print is for the pur- 
pose of making the impression of a hole in the sand, which hole 
is to contain or retain a core that the founder always provides; 
and as the core must fit the print hole, so the size of the print at 
once informs the founder what sized core he must make use of, 
and the hole will be the same. These cores are made of sand 
loam or other materials according to their magnitude, and the 
purposes they are applied to. The moulding of the pipe above 
described, offers a good example. 

Recurring to the pattern for the pipe represented by Fig. 132, 
it will be seen that its two ends are terminated by cylindrical pro- 
jections w w which protrude beyond the flanches, and any one ac- 
customed to pipes will know that these projections do not belong 
to a pipe, and should not be there; nor will they appear when the 
piece is cast, for these projections are merely the prints that de- 
termine the size of the bore, and provide for the support of the 
core, which is to produce it. If this pipe is three inches diameter 
on its outside, and the thickness of the cast pipe is to be half an 
inch, then the prints w w must each be two inches in diameter, 
which will of course leave half an inch all round for the thick- 
ness of the metal of the pipe. If prints of only one inch in diame- 
ter had been left, then an inch core only could be introduced, and 
the pipe would have been an inch thick of metal. The diameter 
of the print therefore determines the size of the core to be used, 
and consequently the size of the bore or hole, while the extreme 
distance between the two ends of the prints determines the length 
of the core. In moulding this pattern, therefore, the two prints 
w w, will make their impressions in the sand, as well as the rest of 
the pattern, and the hollow spaces they leave are for the recep- 
tion and retention of a core that the founder has to prepare, and 
which when placed in its proper place in the mould, will occupy 



348 ON BUILDING MATERIALS, 

the position w w, and of the two exterior dotted lines in the figure 
which show the outlines of the core. In the fornnation of cores 
several things have to be attended to. The core must be of such 
materials as will resist the heat and pressure of the iron, and yet 
it must not bake into so hard a substance as to prevent its removal 
from the hole when the casting is finished. Long cores, (particu- 
larly when used horizontally,) must be very stiff, strong, and inca- 
pable of bending, for iron in a fluid state has a buoyant power of 
more than half that of quicksilver, and will float or bear up any 
thing lighter than itself; and as the iron first runs into the bottom 
of the mould, it will bear up the core, and break or bend it, if 
weak enough to give way, and in this effort will also force up the 
upper box, and spoil the casting if that box is not loaded with a 
sufficient quantity of pig iron, or is not hooked to the bottom box. 
All long cores are, therefore, made upon iron bars if small, or upon 
tubes or pipes of wrought or cast iron pierced with small holes, if 
the bore of the pipe to be made is large enough to admit the latter. 
Such bars are called core bars, and the tubes core barrels. Fig. 
131, PI. IV., is to illustrate the formation of a long core, and 
p 1?, the iron core barrel in which some of the holes are seen 
near JO. These holes are for the discharge of air, steam, and gas, 
from the inside of the pipe when the hot metal is poured in. These 
barrels are either 7 or 10 feet long, because iron pipes are 
usually cast in 6 or 9 feet lengths, and the core must be longer 
than the pipe. Each core barrel has wrought iron pivots fixed to 
its two ends, as at q and r, so that the barrel can be turned in a 
proper cast iron support by a winch at q. Being thus arranged, a 
tightly twisted band of wet hay is wound round the iron barrel from 
one end to the other, in an even manner, part of which is seen at 
s, and this being secured, the hay is covered over with well beaten 
wet loam mixed with plasterer's hair, to give it greater tenacity, 
and thus a cylindrical coating of loam like t t, is made over the 
hay bands. The loam is well known to founders, and is a sandy 
weak clay, or one that has not enough of clay in its composition 
to burn to a hard stone. The core is made truly cylindrical by 
turning it by its winch against the straight edge of a board, called 
a striking board, placed parallel to the barrel, and at such a dis- 
tance from its axis that the board will scrape off all superfluous 
loam, or show the hollow places to which more loam must be 
added until the core is made truly straight and cylindrical from 
one end to the other. The core thus prepared, is carried into 
another appendage to the foundry called the stove, but which is in 
fact a brick room with an arched covering, and closed by iron 
folding doors, and good fires are kept within this chamber so as to 
make it constantly hot, that it may answer the purpose of an oven 



OF CAST IRON. 349 

for drying cores or other moulds that are placed within it. The 
cores are arranged in racks one above another, and there left till 
they become quite dry and hard, when they are dressed and made 
smooth by rubbing, or by a coarse file if necessary, and they are 
blackened by a mixture of finely ground coal dust and water and 
being again dried are ready for use. To use the core, it is only 
necessary to cut away so much of one or both its ends o o by a 
knife, as will permit the loomed ends of it to fall into the two 
cavities made in the sand by the prints w w, and likewise to cut 
away so much of the sand in both boxes beyond the core prints, 
as will give room for the ends o o of the barrel, and the pivots q r 
to lie in the sand, or even project beyond the ends of the flask; for 
the core barrel and all its appurtenances remain in the mould 
until after the iron has been poured into it. The use of the seve- 
ral parts will now be apparent. The core barrel produces the 
necessary stiffness, and provides for the escape of vapours, and if 
the loom was placed immediately upon it, the heat of the iron 
would bake it into so hard a consistence, that neither the barrel 
or loom could be extracted without difficulty. But the heat is so 
great, that before the iron cools all the hay is burnt away and 
consumed, so that the barrel is easily withdrawn, and only leaves 
a thin tube of baked loom within the pipe, which is taken out by 
long chisels or scrapers for the purpose. Short cores, such as are 
introduced for making bolt holes and the like, are formed of damp 
moulding sand rammed into moulds prepared for the purpose, and 
called core boxes, the sand when formed is taken out, put on iron 
plates and placed in the stove, where a large collection of dry 
cores of various shapes and sizes should be kept, and when dry 
the sand will have sufficient tenacity to permit of its being han- 
dled and placed in the print marks made for its reception, without 
fear of breaking or injury. As a general principle, therefore, it 
must be recollected that whenever holes are required in a cast- 
ing, their places must be indicated in the pattern by prints and 
not by holes. Those unacquainted w-ith the practice of moulding 
will sometimes be at a loss how to place the prints in the most 
advantageous positions for the moulder, and whenever such diffi- 
culty occurs, the best way is to put on the prints exactly where 
the holes are wanted, because this shows the moulder where 
they ought to be, and if they are not placed in a manner conve- 
nient to himself, he will alter them; for prints are only stuck on 
with brads, and should not be glued. Indeed glue should be 
avoided in every part of a pattern if possible, for however neatly 
it may have been managed, the moist heat of moulding sand is 
sure to dissolve it more or less, which causes the sand to adhere 
to the pattern and produce imperfect or rough castings. Nailing 



350 ON BUILDING MATERIALS. 

with brad, or dovetailing are, therefore, constantly resorted to in 
making patterns. If the hollow to be produced in a casting varies 
from the usual regular forms of cylinders, squares or rectangles, 
it is customary for the pattern-maker to furnish the founder with 
a core box, for forming such cores. 

614. Notwithstanding that green or damp sand is almost con- 
stantly made use of for the common run of work in foundries, it 
requires great nicety and is not the best material. The sand re- 
quires to be moistened to a certain extent to enable it to maintain 
the form that has been given to it by the pattern; but if it is made 
too wet, it is exceedingly dangerous to the workmen, for steam is 
generated so suddenly and in such quantities the moment the iron 
is poured into the mould, that it is blown up, and the fluid metal dis- 
persed in all directions. The moulder therefore has to be very 
cautious in damping his sand, to prevent such accidents. But even 
when the mould is safe, the melted iron coming into contact with 
damp sand, and the cold produced by the sudden evaporation, 
never fails to produce a bad effect upon the iron, if it is intended 
to be worked by turning or filing, for it renders the outside very 
hard and refractory, which is an advantage if the casting has to 
be used in the state in which it leaves the sand. All castings that 
have to be cut or worked upon, should therefore be of the third 
variety before enumerated, (604,) or be made in dry sand, 

615. The process for green and dry sand castings, is in every 
respect alike, except that for dry sand, as soon as the mould is 
finished, the flask is carried into the stove, and there opened and 
kept for a day or two, or until the sand has become perfectly dry 
and hard. It is then carried into the foundry, and being properly 
disposed for receiving the metal, a charcoal fire is made round, 
and over it, so as to get the sand in a very hot state before the 
metal is poured into it, and thus the metal runs into a hot and dry 
mould, instead of a damp and cold one; and as the flask is not 
opened until quite cold, the metal receives no chill, and will be 
superior in quality for working upon. Dry sand is worth more 
than green sand casting, because the founder has the same trouble 
and expense in both, with the additional loss of time and expense 
of fuel for drying the mould in dry sand work. 

616. The fourth and last kind of casting, is the most difficult 
and costly, and is called loam-work. It is only resorted to for pro- 
ducing large cylinders for steam-engines, air vessels for forcing- 
pumps, boiling pans for sugar refiners, soap-makers, and other 
manufacturing purposes, and generally for any thing that is so 
large that a pattern would be inconvenient, or that flasks could 
not be made sufficiently large to contain and mould it, without 
having them of enormous weight, and unmanageable dimensions. 



OF CAST IRON. 351 

Loam work is carried on from drawings without any pattern, and 
is so different from sand work, that those foundries that undertake 
it, have distinct sets of men called sand and loam moulders; for 
loam moulding is indeed modelling in clay or loam. It constantly 
requires a very powerful crane in foundries where it is undertaken, 
and a dry location, or one free from springs, to the depth of at 
least 10 or 12 feet, because the casting always takes place in an 
underground pit, w4uch must be deep enough to hold the thing to 
be cast without any part of it rising above the surface of the 
floor, or its lower part being exposed to natural humidity. A de- 
scription of the manner in which a large steam-engine cylinder is 
moulded and cast, will suffice to explain how loam casting in gene- 
ral is conducted. The moulding takes place on the floor of the 
foundry, and is carried on upon a circular foundation plate of cast 
iron, made for the purpose, and which must be at least one foot 
more in diameter than the proposed cylinder when finished. This 
plate is so placed, in a horizontal position, that the jib of the 
crane can sweep over its centre, and it has three short arms pro- 
jecting from its circumference, to which chains are attached and 
carried up to the crane, for elevating the plate in a perfectly 
horizontal position whenever required. The chains having been 
adjusted as to length, are taken down and put away. The sweep 
is now erected, which is a strong bar of iron longer than the cylin- 
der to be formed, its bottom is formed into a shoulder, with a cy- 
lindrical pivot which works in a corresponding hole in the centre 
of the foundation plate, and its top has a similar pivot working in 
a bearing, in a cross piece of timber, so that the bar thus fixed in 
a vertical position, can revolve freely, but without shaking, and is 
set truly perpendicular by a plumb rule. The upper end of the 
vertical bar carries one or two arms one above the other, but 
both parallel, and at right angles to the bar, and these arms have 
many bolt holes, with screw bolts passing into them, by which 
striking boards may be fixed to them in any required position. 
The first striking board to be used for a cylinder has a perfectly 
straight inner edge, which is placed towards the iron spindle, pa- 
rallel to it, and at a distance from it equal to the intended radius 
of the inside of the cylinder. This board is screwed to the arms 
and extends down to within an eighth of an inch of the foundation 
plate, and being so disposed its inner edge will of course describe 
a cylinder when turned round upon the vertical iron bar as an 
axis. The building of the cylinder mould now begins, and this is 
done with very soft or sammy bricks (493) laid four inches thick 
in wet loam, instead of mortar, upon the foundation place, taking 
care that the outside of every brick shall be at least an inch with- 
in the inside edge of the striking board, as it is moved round. A 



352 ON BUILDING MATERIALS. 

hollow cylinder of brickwork will in this way be produced, which 
must be a few inches more in height than the intended cylinder. 
The wall being finished, is next to be plastered with the same 
wet beaten loam and hair used for covering core barrels, and which, 
when it becomes about an inch thick all round, will touch the 
striking board and be scraped otF by it, until a fair and smooth 
loam cylinder is produced, and which is the core of the intended 
iron cylinder. It now stands till it is dry, and this operation is 
expedited in damp weather by putting ignited charcoal into the 
brick cylinder. The striking board is then shortened or taken up 
about two or three inches, for striking or forming a horizontal 
plate or layer of loam upon the foundation plate, to protect it 
from heat, and to form the underside of the bottom flanch of the 
cylinder. This work being dry, the cracks or fissures that have 
occurred in it are mended or plastered up with damp loam, and 
the whole is painted over with a thick coat of coal and charcoal 
powder and water, and the print holes for the bolt holes of the 
bottom flanch are set out by a thin template of wood and cut out 
by a chisel. The thickness of metal for the proposed cylinder 
having been determined, say 1^ inches, and the flanches at 2 inches, 
the striking board must now be raised 2 inches higher, and be 
placed 1-^ inches further from the centre, when another coat of 
loam prepared without hair is put on, and struck round by the 
board, and this coat we will call the representative coat, because 
it holds the place that the iron is to have, and represents its form. 
If any bands or mouldings are to surround the cylinder, they must 
be made on this coat, and are produced by cutting the profile of 
them in the inner edge of the striking board. The bottom flanch 
must also be struck and formed. This coat of loam being dried, 
must in like manner be black-washed, the blacking answering the 
purpose of parting sand, and preventing one coat of loam adhering 
to another. The striking board is now done with, and may be 
taken down. Two semicircular plates of iron, each with three 
projecting arms as before, and with their insides made circular to 
suit the curvature of the lower flanch, are now placed opposite to 
each other on the foundation plate, to serve as foundations for the 
external case of the mould, which is built in two semi-cylindrical 
halves upon them. The lower part of the representative coat 
and flanch are first covered with wet loam and hair which is back- 
ed or supported by soft brickwork as before, but which in this 
case will require to be twice as thick, and these walls are made 
with straight joints over the ends of the semicircular plates that 
they may be taken asunder when dry. This outer wall, or jacket, 
as it is generally called, having been carried to the full intended 
height of the cylinder, the upper flanch must be struck upon its 



OP CAST IRON. 353 

top, by a short striking board fixed for the purpose, and lastly, a 
circular cake of loam is struck on another iron plate to cover the 
top of the flanch. The several pieces being well dried are now to 
be separated by the crane; the two halves of the jacket or external 
casing are nnoved laterally away, and the representative coat is 
carefully broken and cleared away as useless. The pit is dug, 
and nnade level in its bottonn, the first foundation plate with the 
core upon it is taken up by the crane and chains, and lowered into 
the pit; the two jacket pieces are next lowered in the sanne manner, 
and put in their propex places; the cores for the bolt holes of the 
lower flanch having been arranged in their proper positions, and 
now the sand dug out of the pit is returned again by shovels, and 
carefully rammed round the outside of the mould, which is gene- 
rally further secured from separation by an iron chain being wound 
round it; lastly, the loam cake or covering is placed over the 
mould, having a gate and vent holes made in it, when the whole 
is buried in sand by filling and ramming the pit to its former level 
with the foundry floor, when the mould will be ready to receive 
the melted iron. 

617. Heavy loam castings, such as have been described, cannot 
be made from a cupola, but require a large charge of metal and a 
wind furnace; and the quantity of metal is too great to be carried 
in shanks or ladles, therefore a gutter is generally made in sand 
from the gate of the mould to the tap hole of the furnace, and 
when the tapping takes place the metal flows immediately into 
the mould. In getting the casting out of the pit, the sand has 
again to be dug out and thrown to the surface, the jackets are 
broken to pieces, and the fragments brought up in baskets to 
lighten the load, and chains must be fixed round the remainder 
for hauling it up from the pit by the crane. Such is the process 
that must be gone through with slight variations in all loam 
castings. 

618. It is sometimes desirable to produce castings of more than 
ordinary density and compactness, as in forming the rollers before 
described (580,) for making bar iron and sheet metals. This is 
done by placing the mould in the bottom of a deep pit, and hav- 
ing a gate and vent of several feet in perpendicular height, while 
the metal is to be poured to the full surface of the gate; and as 
fluids press in all directions according to their perpendicular 
height, so of course a great pressure and condensation is produced 
on the casting at the bottom of the pit. The gate, in this case, 
should not be perpendicular, or the heavy iron in falling so great 
a height might break or injure the mould, and would carry down 
air with it which would make the casting show air bubbles. A 
large gate and vent having a small connexion with the casting 

45 



354 ON BUILDING MATERIALS. 

that they may be easily broken off, is always an advantage, be- 
cause all metals shrink much in cooling, and this shrinking takes 
place to the greatest extent in that part of the metal that remains 
longest fluid. This is the case with the gate, therefore the con- 
traction takes place in that and does not deface the casting, but if 
the gate does not contain metal enough to supply the deficiency, 
the shrinking will extend to the casting itself, and may spoil it. 

619. Castings of any kind appear rough, when they leave the 
mould, and require to pass through the hands of a workman call- 
ed the trimmer. His business is to cut off the gates, vent pieces, 
and all superfluities, by the cold chisel and hammer; to take 
out and remove all cores or remains of cores from holes or pipes; 
to scrape and file the outsides and remove any sand that may 
adhere to the castings, and to finish and improve their surfaces by 
rubbing them with charcoal and coke. He likewise performs 
another duty that would be better let alone, as it often gives the 
Engineer great trouble and vexation; that is hiding all blemishes 
and defects in castings by running lead or cement into holes or 
bad places, so as to render them invisible, in order to make cast- 
ings pass for perfect, which would frequently be returned upon 
the hands of the founder, had the defects been apparent on the 
delivery. 

620. From the foregoing description it will be seen that one of 
the most difiicult and delicate operations the moulder has to per- 
form, is the raising a top flask from a bottom one after moulding 
a solid pattern, without breaking down much of the sand. This 
difficulty arises chiefly from his having no means of access to the 
pattern for the purpose of loosening it; for whenever a pattern is 
gently struck by a hammer, it becomes detached from the sand, 
and may, in most cases, be raised with ease. On this account 
solid patterns or patterns in single pieces, are never made when 
they can be avoided; but every pattern should consist of two 
halves, put together with steady pins, for preserving the position 
of the parts, and is so placed in the flask that the joining may be 
horizontal; consequently on separating the two boxes, one half 
of the pattern remains in the lower, and the other in the upper 
box, and the difficulty of taking them out of the sand is much 
diminished, at the same time that advantages in the facility and 
perfection of moulding are presented. 

621. In order to increase the facility of withdrawing patterns 
from the sand, it is essential that their surfaces should be smooth 
and regular, on which account patterns that are very frequently 
used are varnished and polished. It is also quite necessary that 
every pattern should have draught as it is called, that is, the 
lower part that is to sink into the sand must be smaller, though 



OP CAST IRON. 355 

in a small degree, than the upper part; so that whenever the pat- 
tern is raised in the shghtest degree, it may become detached 
from, and independent of the sand. If a pattern is Jarger below 
than above, it will be impossible to withdraw it without tearing 
up the sand and breaking the mould; while if it diminishes in the 
slightest degree no such effect can occur. 

622. Another very important point for the Engineer to attend 
to in making his patterns, is the contraction of the metal in cool- 
ing, which constantly causes the finished casting to be less than 
the pattern from which it is made. Different kinds of iron con- 
tract in different degrees, and the white or No. 3 pigs most of all, 
so that the exact quantity of allowance is best learnt by dealing 
with a foundry and observing the diminution that really occurs. 
The average allowance that is made is one-eighth of an inch to 
each foot of extension for medium or No. 2 iron, but this is rather 
too much for No. 1, and not enough for No. 3. From this cause, 
if we want a pipe or a column to be exactly 9 feet long, the pat- 
tern must be made 9 feet 1^ inches long, or nine-eighths of an 
inch has to be allowed, and this same principle applies to the 
thickness as well as the length of all castings, and must be particu- 
larly attended to in cogged mill wheels. The cavities for the 
wooden cogs of an iron mortice wheel, are all produced by cores, 
for which purpose a core box is indispensable, that all the holes 
may be alike; and the prints for such cores are always set in pairs 
opposed to each other on the inside and outside of the rim of the 
wheel pattern. 

623. In the formation of all patterns, especial care must be 
taken not to introduce more metal than is necessary for due 
strength and good appearance, because a superabundance of 
metai greatly enhances the weight and cost of the work, and 
what is of more importance, there is not the same proportional 
security as to strength in very large castings as will be obtained 
from an equal area of smaller ones. This is brought about by 
the natural contraction of the metal in cooling, and the impossi- 
bility of producing any change in the shape of a piece of cast 
metal the moment it becomes hard or sets. In moderately sized 
castings the wsetting takes place throughout the whole mass at 
once, and all its parts solidify at the same instant, or nearly so, 
therefore a uniformity of contraction occurs. But in very large 
castings, it frequently happens that their outsides, which are in 
contact with the mould, will cool and set all around, and thus in- 
close a considerable portion of yet fluid metal in the centre that 
will not set for some minutes afterwards. When it does so set 
and cool, it must contract, and in doing so would draw the outside 
inwards, and diminish the whole size of the casting; but the out- 



356 ON BUILDING MATERIALS. 

side is set and cannot change its figure, therefore the inside is 
compelled to contract alone, and in doing so frequently runs into 
crystalline forms, and leaves cavities that are called air bubbles, 
but which are in fact perfectly empty spaces, similar to the torri- 
cillian vacuum of the barometer. Such conformations are con- 
stantly found when very large and heavy solid shafts break, and 
the iron is said to have a honey-combed grain. This is avoided 
by making shafts and columns hollow or tubular, and experience 
proves that the same quantit}^ of metal in a hollow shaft or column 
will produce much greater strength than if it were solid. 

624. These considerations, however, belong more particularly 
to the next chapter, where they will be explained and investigat- 
ed, and where it will be shown that the same materials are capa- 
ble of producing very difTerent degrees of strength, depending 
upon the manner in which they are placed and used. Thus it is 
known to every one, that if an inch pine board of 12 inches wide, 
and 10 feet long, is placed with its broad side upwards to be used 
as a shelf, it will support very little w^eight without first bending 
and then breaking; but if this same board is placed with its thin 
edge upwards, and any means is resorted to for preserving it in a 
right lined direction, a most enormous weight in comparison to 
the first it could bear, may be hung to it without fear of its frac- 
ture. This principle is constantly resorted to in using cast iron; 
for a thin plate of cast iron, like a board, can bear but little, and 
from the brittle nature of the material, will break upon a slight 
bending; but if two such plates are used conjunctively, and one is 
placed flatwise like y y, Fig. 133, Plate IV., and the other, z, is 
put under it with its thin edge upwards, then the position given 
to z will prevent y y from bending downwards, and consequently 
it cannot break until such a force is applied above it as will break 
z, because until that is done y y cannot bend sufficiently to break. 
In practice two bars are seldom used in this manner, but the two 
are conjoined or cast in one piece, as shewn in the figure, which 
is a transverse section of a cast iron beam fit for a breast-summer 
for carrying a wall or a girder for supporting a floor. The figure 
likewise shews the draught that should be given to the pattern to 
make it deliver from the sand. Such a beam would be cast in 
the direction in which it is drawn in the plate, therefore every 
part is made narrower below than above. The two edges of the 
horizontal plate y y incline, so that the bottom side is not as wide 
as the top, and the strengthening plate z, which in foundry work 
is called a. feather, is wedge-shaped, or thinner at the bottom than 
the top; and as the last contraction of cast iron in cooUng always 
occurs where there is the greatest quantity of metal, and this is 
generally where two plates or surfaces intersect, so when surfaces 



OP CAST IRON. 357 

are joined at right angles, there is more chance of their cracking 
and even separating there, than any where else, so to avoid such 
accident, it is prudent, and very customary, to introduce a fillet 
or ovalo (115) into all retiring right angles, to give additional 
strength; and accordingly such a one is shewn at a a in this beam; 
and the same precaution is also necessary in the similar angle 
made bv the junction of a pipe v^'ith its flanch as shewn in Fig. 
132. 

625. Fig. 128, Plate IV., is a front view of a pattern for a cast 
iron wheel of great strength, and Fig. 129 is a transverse section 
of the same, and these figures are introduced to show how the 
principles above explained are applicable to the formation of 
wheels, and a vast variety of articles now made of cast iron; in 
the planning of which the Engineer must always endeavour to 
obtain the greatest possible strength out of the smallest possible 
quantity of material, not only as before observed, for saving ex- 
pense in the original cost of construction, but likewise in the 
transportation of the materials, and for the equally important pur- 
pose of preventing unnecessary weight upon the moving bearings 
of machines, and of diminishing inertia and friction, by which 
greater freedom of motion is induced, and the appearance of the 
construction improved: for light and delicate machinery is always 
more pleasing to the eye than that which is clumsy from being 
overloaded with material. 

626. Suppose it is desirable to construct a strong cast iron 
wheel that shall present a face or surface of 4 inches wide to the 
ground or surface on which it is to run. Instead of making the 
felly or circumference a ringof 4 inches square in metal, or even 
4 inches wide by 2 inches thick, and putting strong cylindrical 
spokes like those of a carriage wheel to support it, the whole, 
with the exception of the boss or nave, may be made of metal 
not exceeding three-quarters of an inch in thickness, with greater 
certainty and more strength by adopting the construction shewn 
in the figures. The nave or boss 6 must of course be a solid 
block of metal, as it requires length of bearing for the axle-tree, 
and has to support all the other parts of the wheel, but it may be 
tapered on both sides like two truncated cones, as seen in the 
sectional figure, and this will give it good draught from the 
sand; a a are the prints for the cylindrical core that is to form 
the hole through the centre of the wheel. The six arms c c, and 
the internal ring// may be made of J inch board, having a width 
proportioned to the load to be carried. The external ring e e is 
fixed on the edge of the thin internal ring// and must of course 
be 4 inches wide, but need not exceed finch thick, but it will be 
better to make it a Httle thicker in the middle of the inside, not 



358 ON BUILDING MATERIALS. 

only to produce draught, but to increase strength. To give 
strength and stiffness to the arms, feathers d d are applied on both 
sides of them instead of on one side only, and these feathers should 
be thinnest on their outer surfaces. A transverse section of each 
arm will therefore present the form of a cross as seen at i, Fig. 
129, and thus not only the arms, but the circumference will be 
strengthened by flat pieces at right angles to each other, and suffi- 
cient strength for any required purpose may in this way be ob- 
tained. 

627. If the opposite mode of construction had been adopted, 
and a heavy periphery had been connected to a solid boss or 
nave, by spokes of much smaller dimensions, such a wheel might 
be cast, but the chances are greatly against its being raised out 
of its mould in an entire state; and if that should happen, there is 
the greatest probability of its breaking by a very slight shock or 
concussion in after use, owing to unequal contraction, and the 
metal not being in a state of what may be called tranquil equili- 
brium throughout its substance. The spokes being so much smaller 
than the other parts, will set and cool, and arrive at their maxi- 
mum of contraction while the other parts are hot or even fluid, 
and this inequality of contraction will, in all probability, cause a 
separation of the spokes, or some of them, from the nave or from the 
circumference, or if it does not take place on the first cooling it 
will occur afterwards, if the wheel should be struck with a ham- 
mer, or receive any shock or vibration that will permit the un- 
natural tension to overcome the cohesion of the weakest part. 
These accidents to castings and their spontaneous fracture are 
very common, and the blame frequently attaches to the founder, 
who is accused of having used bad iron; whereas the real cause 
will generally be apparent to any one acquainted with the nature 
of cast iron, and may be traced to an injudicious form of the cast- 
ing; and such accidents can only be guarded against^ by such 
a skilful disposition of the quantities of metal that no one part 
shall have an advantage over another. If one part of a casting 
is made thick, others that join it must be thick in proportion, and 
no attempt made to unite very large and very small pieces except 
by rivets or screws, for they must be made separately. 

628. It is on this account, as much as for the convenience of 
transportation, that the large fly wheels of steam engines, and 
cog wheels for mill work are made in separate pieces, consisting 
of the central boss, arms and segments, which are afterwards 
united by screw bolts and nuts; and it is found that wheels, shafts, 
and other heavy pieces, are more strong, and trustworthy, when 
so put together, than such as are cast in single pieces. Another 
advantage also attends the union of separate pieces, which is that 



OF CAST IRON. 359 

owing to unequal cooling and contraction, (however much guarded 
against,) it is nearly innpossible to obtain a large flat casting with- 
out Sonne little warping or winding, which cannot be cured in a 
single piece. But when large wheels are put together there is an 
opportunity of curing this defect, if it exists, in the making of each 
joint, in consequence of which, built wheels, as they are called, 
can generally be made to run and work with more truth and 
accuracy than such as are cast in single pieces. 

629. Cast iron work for engineering or mechanical purposes is 
always sold by weight, except in the instances of straight water 
or gas pipes, and rail-road plates, and these being of uniform size, 
take, on an average, the same quantity of iron and labour, and 
can therefore be charged by the running yard, which for these 
articles is a more satisfactory method, as it enables the Engineer 
at once to name the cost of any given quantity of such materials. 
But if a pipe or plate of more than ordinary weight, or of peculiar 
construction is required, it is not included in measure, but is 
weighed. 

630. Pattern making, from its nicety, and requiring the best of 
workmen and materials, is always expensive, and a single pattern 
frequently costs more than the casting made from it. The ex- 
pense of patterns always falls on the employer, whether he makes 
them or has them made at the foundry; and they are his property, 
and should be preserved, or sent back with the castings. Of 
course, therefore, in making estimates, the expense of the pat- 
terns must be added to the cost of the metal. But many large 
foundries are in the habit of keeping patterns of their own, for all 
such things as are in common request, and of which great num- 
bers are required, and in this case the founder adds a small per 
centage for the use of his patterns upon the charge he makes for 
the iron, and where this is done, it is a great saving in point of 
expense as well as time to the Engineer. Messrs. Galloway, 
Bowman & Co. of the Caledonian foundry, at Manchester, in Eng- 
land, publish a list of the patterns they thus keep, and which 
amounts to upwards of five hundred bevil and spur wheels of all 
sizes and strengths which are specified, together with the number 
and pitch of their cogs, besides about one thousand varieties of 
shafts, gudgeons, coupling boxes, pullies, pipes, frames for presses, 
and other articles, so that the Engineer can find almost every 
article he stands in need of, for the ordinary construction of mills, 
presses, rail-ways, gas and water-works, spinning machinery and 
power looms, without having occasion to construct patterns of his 
own. 

631. The only method of estimating the expense of cast iron 
work is by measuring and calculating the solid contents of castings. 



360 ON BUILDING MATERIALS, 

or else reducing them to board measure, (566,) and computing 
the weight in either case from the known weight of iron. The 
average specific gravity of cast iron is 7.207,* and as striking out 
the decimal point from the number expressing the specific gravity 
of any given substance, at once gives the number of avoirdupois 
ounces that a cubic foot of that substance weighs, so a cubic foot 
of cast iron will weigh 7207 ounces, or 450 pounds and 7 ounces. 
But as bolt holes and small cavities in castings are never deducted, 
so foundries usually disregard the 7 ounces, and call a cubic foot 
of cast iron 450 pounds, the twelfth part of which, or a superficial 
foot of iron one inch thick, will weigh 37j pounds, or 600 ounces, 
and a single cubic inch 4.163 ounces. Solid castings are, there- 
fore, cubed and compared with the weight of the cubic foot or 
inch, while hollov^ castings, such as hollow cylinders or pipes, are 
measured superficially, and estimated as if they were one inch 
thick. If they are more or less than an inch, then the product 
obtained by one inch is increased or diminished accordingly. 
Thus if the cylinder is two inches thick, the product is doubled. If 
one and a half inches thick, only half its amount is added, or the 
same quantity subtracted if the iron is but half an inch thick, and 
so for other thicknesses. 

' 632. The weight of solid castings may be determined with suf- 
ficient accuracy for many purposes by weighing the wooden pat- 
tern and multiplying that weight by 14.4 if the pattern is made 
of white pine wood; or by 10.8 if made of hard mahogany; because 
cast iron is heavier than these varieties of wood in very nearly 
these proportions. This is an expedient that iron founders con- 
stantly resort to for determining the quantity of iron to be put up 
or melted, in order to insure having iron enough in the furnace 
for the intended purpose (603); and Engineers may resort to it when 
they wish to become acquainted with the approximate weight of 
any casting for which the pattern has been prepared. Patterns 
are sometimes called models, but pattern is by far the most com- 
mon name by which they are designated. 

Steel. 

633. Steel cannot be considered as constituting a building mate- 
rial, and therefore in strict propriety ought not to be included in 
the present chapter. It is however of so much importance in the 
building art, as constituting the only material of all cutting tools, 
and is so frequently used in machinery, that some information as 
to its properties cannot fail to be interesting to the Engineer. 

* Dr. Thomas Young's Lectures on Nat. Phil., Vol. II. p. 503. 



OF STEEL. 361 

634. Steel is an artificial or factitious metal, being produced by- 
causing bar or malleable iron to unite with a quantity of carbon, 
but at the same time, a less quantity than that which it held be- 
fore it was converted into bar iron. Cast iron generally contains 
about 5 per cent, of carbon, while steel seldoms holds more than 
from 1 J to If per cent. The formation of steel is therefore par- 
tially bringing iron back again to its primitive state, and yet the 
variation produced by this small difference in the quantity of car- 
bon, produces a great difference in the two metals; for cast iron 
is always more or less brittle and cannot be forged or welded, 
while steel yields readily to the hammer, and may be forged and 
worked with nearly the same facility as bar iron. It neverthe- 
less requires more care in the heating, for steel is fusible, though 
in a less degree than cast iron, and by over heating, it looses all its 
valuable properties, and in the language of the workmen becomes 
burnt. 

635. Steel is made by selecting the best and most pure bars of 
iron, and inclosing them in a tight box with powdered charcoal, 
in which state they are kept in a furnace exposed to a very 
violent heat for about a week, and on being withdrawn, the box 
with its contents is allowed to cool very slowly, before it is opened. 
During this process the iron bars combine with the necessary 
quantity of carbon, and become converted into steel. The pro- 
cess is called cementation. The steel made in this way exhibits 
many blisters like air bubbles on its surface, and hollow cavities 
of a similar kind occur in the middle of the bar, on which account 
steel in this state is called blistered steel. Steel is very commonly 
sold and used in this state, but it requires considerable forging, 
that is hammering in the red hot state, to get rid of the hollows 
and blisters, and to render it equally close and compact through- 
out its whole substance. This forging is very frequently perform- 
ed at the place where the steel is made, by means of heavy ham- 
mers driven by machinery, and called tilt hammers, and when the 
blisters and cavities have thus been got rid of and the bar is 
rendered uniform throughout, it is sold under the name of sheer 
steel. 

636. Blistered steel instead of being forged, is occasionally broken 
into short pieces, which are put into large crucibles having close 
covers, and containing powdered charcoal, and in this state is fused 
by heat, and cast into ingots about 30 inches long, in which state 
they pass the grooved rollers like bar iron, (580,) and are con- 
verted into bars which are called cast steel, and this is considered the 
best and purest kind, and is more used than any other for cutting 
tools. 

637. In selecting steel for use, regard must always be had to 
46 



362 ON BUILDING MATERIALS. 

its qualities, which seem to depend on the quantity of carbon it 
contains, and the care with which it has been manufactured; hence 
there is a great difference in the quality of steel, and that manu- 
factured by some makers has a decided preference over others. 
For making springs, the steel should contain but a small quantity 
of carbon. Articles of cutlery require a larger quantity, and files 
and all tools for cutting the hard metals, require the largest dose, 
and should therefore always be made from cast steel. 

638. Notwithstanding steel is but a variety of iron, still it differs 
from that metal in several important points. It is of a lighter 
colour, and always appears granulated instead of fibrous. It is 
susceptible of a much higher polish, and is less liable to rust. It 
has a greater specific gravity, and is capable not only of being 
rendered much harder, but much more elastic than iron. When 
touched by a strong acid it turns nearly black. It is less power- 
fully attracted by the magnet, but retains permanent magnetism 
which cannot be communicated to iron. It is fusible, although 
capable of welding, but its most valuable and distinguishing pro- 
perty is the facility with which it may be hardened or softened to 
almost any required extent by different degrees of heat, the ap- 
plication of which is called tempering. 

639. Steel in its first state is flexible and nearly as soft as bar 
iron, but if a piece of it is heated to a low red or cherry heat, and 
is then suddenly cooled by plunging it into cold water, it becomes 
intensely hard and brittle, and will not bear the slightest bending 
without fracture. All files and tools for cutting hard metals must 
therefore be hardened in this way; but it renders them subject to 
the inconvenience of very readily chipping or breaking on their 
edges, from the extreme brittleness of the metal. If, however, the 
hardest steel is heated to redness, all its hardness disappears again, 
and by thus heating it and permitting it to cool very slowly, it 
becomes almost as soft as iron. If the steel is polished or made 
bright by grinding while in its hard state, it will assume a succes- 
sion of brilliant prismatic colours upon its surface when heat, much 
below redness, is applied to it for the purpose of softening it. 
These colours are constantly in the same order of succession, and 
bear relation to the hardness of the metal; and if the steel is cooled 
by plunging it into cold water at the moment any colour makes 
its appearance, the hardness that is peculiar to such colour be- 
comes permanently fixed in the steel, and this operation, which 
requires care and dexterity, as well as experience on the part of 
the workman, is called tempering. Steel in its hardest state, has a 
peculiar white appearance, by which its hardness can be judged 
of by an experienced eye without trial, provided the surface is 
free from oxydation. On applying heat to such hard steel, the 



OP STEEL. 363 

first colour that makes its appearance is pale yellow, which be- 
comes darker or more inclining to a tawny brown, if the heat is 
continued. The medium yellow is by workmen called straw 
colour, and it is on the appearance of this colour, that the steel 
must be cooled, to obtain the most favourable temper, for all tools 
for cutting brass, iron, and copper. If, instead of being cooled, 
the heat is continued upon the steel, the brownish-yellow changes 
to that beautiful blue colour so common upon steel implements. 
The blue temper is also called the spring temper of steel, because 
when blue, it is much less hard than while straw coloured, and it 
now possesses its highest degree of elasticity. Steel at the straw 
coloured temper, is so devoid of elasticity, that it will not bear the 
slightest bending without breaking, but at the blue temper it maj 
be bent to a great extent without fracture, and on being released 
from the bending force, will revert to its former figure. All steel 
springs should therefore have the blue or spring temper, the 
nature of which is well exemplified in the main spring of a watch. 
The various tools for cutting wood should also have this temper, 
which will render them hard enough for their intended purpose, 
while they will not be so liable to be broken as when they are 
harder. Should the heat be continued upon the steel beyond the 
appearance of the blue, it will assume a reddish or violet tint, 
and the steel is then too soft for the generality of tools, and is 
flexible, but possesses but little elasticity or tendency to revert to 
its former figure, but will retain any shape into which it may be 
bent, and if heated to redness and slowly cooled, it will be black 
like iron, and is in its softest state. Of course, steel is constantly- 
worked and formed in this state, and is not hardened and temper- 
ed until the article is finished, all but receiving its last polish. 
Drills and other tools of hard steel, that are subject to rapid mo- 
tion, frequently become so heated by friction during their use, that 
they soften themselves and become inefiicacious, in which case 
there is no alternative for restoring them, except by the above 
described process of hardening, and afterwards tempering them; 
for every piece of steel must be made hard before it can be re- 
duced to a lower temper. On this account chisels and many work- 
ing tools are sold hard, in order that the workmen who are to use 
them, may let them down, or temper them to their own wishes; 
and this can be very conveniently done by placing them on a 
sufficiently large bar of iron previously made red hot, and having 
a bucket of cold water at hand to plunge them into the moment 
the desired colour has appeared. Saw blades, swords and other 
articles of steel, that expose considerable surface, are very diffi- 
cult to temper equally, and the heat is best applied to them by 
placing them in a bath of boiling oil, or of melted tin, or lead, so 



364 ON BUILDING MATERIALS. 

that every part shall be simultaneously exposed to the same ele- 
vation of temperature. 

640. Steel has the same faculty of welding as iron, and it will 
not only unite with itself, but with iron in this way, so that tools 
and other articles are very seldom made wholly of steel, but a 
thin piece is welded on to iron when a cutting edge is requir- 
ed. The manufacturer takes this additional trouble to save the 
expense of steel, which usually costs from three to four times as 
much as iron; and it is equally advantageous to the consumer, for 
hardened steel is always more or less brittle, and articles made 
wholly of steel, would be very apt to break; but as the quantity 
of iron usually predominates, its tough and flexible property if 
good, adds a strength to the steel which could not otherwise be 
obtained. 

641. The same object is obtained in another way, by the pro- 
cess called case hardening. Articles to be finished in this manner 
are made wholly of the best iron, and are filed up, finished, and 
rough polished. They are then inclosed in a close iron box, in 
which they are imbedded in charcoal, a part of which should be 
produced by burnt leather or bones. In this state the whole is 
exposed to a full red heat in a furnace, for a few hours, when the 
whole external surface of the iron will be converted into steel, 
penetrating no deeper than the thickness of common paper, but 
which thin casing will bear hardening, tempering, and polishing, 
thus giving the article all the external characters and advantages 
of steel, while the unchanged iron within gives strength, or rather 
tenacity. 

642. Brass 

Is not a building material, but is much used by the practical 
Engineer, who should therefore be acquainted with its properties. 

Brass is an alloy or artificial metal, and is distinguished by four 
principal varieties, called Jine yellow brass, gun metal, bell metal, 
and pot metal or cock metal. The first is a compound of copper 
and zinc, in the proportion of five parts of the first to three of the 
latter, which produce the beautiful yellow metal of which philo- 
sophical instruments, and articles of household ornament are form- 
ed. It is but little used by the Engineer, and then only for the 
ornamental parts of steam-engines, or for small wheelwork. It is 
ductile, tough, and very tractable in the hands of the workman, 
and bears a fine polish. 

643. Gun metal is of a reddish-yellow colour, and is a com- 
pound of nine parts of copper, and one part of block tin, to which 
sometimes a little zinc is added. It is distinguished by its peculiar 



OP BRASS. 365 

toughness, and derives its name from all brass cannon being form- 
ed of it; its toughness preventing them from bursting. It is much 
used by the Engineer for the bearings in which the iron gudgeons 
or pivots of all machinery turn, and also for the formation of 
steam and water valves, and the cylinders or working barrels of 
pumps. It is less easy to work than yellow brass, but is stronger 
and more durable. 

644. Bell metal, so called from its being the composition with 
which bells are cast, is made of six parts of copper, and two of 
tin. Its colour is much paler than either of the foregoing, inclin- 
ing to a reddish-white, or very pale yellow, and it is so hard and 
brittle, that it will not bear the slightest bending without break- 
ing, and can scarcely be touched by the file or other tools. It 
can therefore only be altered in form by chipping with the cold 
chisel or grinding. It is used by the Engineer for the bearings of 
gudgeons, when extreme hardness is required, and in other places 
where steel would be objectionable from its liability to oxydation, 
a property which this metal possesses in a very slight degree. 

645. Pot or cock metal is the cheapest and worst kind of brass, 
and is composed of copper and lead usually in the proportion of 
2 to 1, or sometimes in equal quantities. Of this metal all water 
and steam-cocks are made, as well as the various pieces of brass- 
work made use of by plumbers. The metal has a handsome 
tawny yellow colour, and takes a good polish, but is soft, and 
at the same time very brittle, and possesses very little toughness 
or strength, but it files and works readily, and when not subject to 
blows or concussions is very durable. 

646. Copper, Lead and Zinc 

Are principally used in the rolled or sheet state, for covering 
roofs, forming gutters for water, or pipes for its conveyance. Sheet- 
lead is sometimes cast upon a flat bed of sand prepared for the 
purpose, when it is called cast lead; but of late years it has gene- 
rally been prepared by passing it between smooth cast iron rollers, 
as is always the case wuth sheet copper, and then it is called 
milled lead. Milled lead is preferable to cast lead, because it can 
be made thinner and more uniform in thickness, and is not subject 
to the small air holes or bubbles that cannot be avoided in casting 
sheets of lead. Lead pipes of diameters less than two inches, are 
usually cast without a longitudinal joint, but larger pipes require 
to be turned up out of sheet metal and soldered. Formerly lead 
pipes could only be cast in short lengths, of about 30 inches each, 
which were burnt together to form a long pipe. Such burning 
consists in placing the two ends that are to be connected together, 



366 ON BUILDING MATERIALS. 

in a brass mould made for the purpose, introducing a polished iron 
core, and then running melted lead upon the joint until by the 
continued application of its heat, the two contiguous ends of the 
pipe are fused, and join to the new metal introduced. Now, lead 
and copper pipes are generally drawn in the same manner as 
wire, so that they are produced of a uniform size, and in lengths of 
12 to 16 feet. An iron triblet or polished rod is introduced into 
the pipe while it is drawing, to preserve the magnitude of the bore, 
and this is withdrawn w^hen the pipe is finished. All copper pipes 
are turned up from sheet metal, and the joint ought to be brazed 
and not soft soldered. Zinc is applicable to many of the purposes 
for which copper has been used, but being of a more brittle 
nature is more liable to crack than either of the above metals. 
From the soft and pliable nature of lead, the Engineer makes fre- 
quent use of it in filling up the joints between iron pipes, and it is 
likewise used in a state of fusion for connecting iron to stone. 

647. Lead, copper, and zinc are always sold by weight, but in 
the sheet state are designated by the weight of metal in a square 
foot. Thus four pound lead, which is the thinnest sheet lead that is 
made, contains 4 pounds of metal in the square foot, and is —^ of 
an inch in thickness. Six pound lead is J^ of an inch thick. 
Eight pound lead is i thick, and ten pound lead i of an inch. 
Quarter inch lead, which is as thick as it is generally used, is very 
nearly 15 pounds to the square foot. Sheet copper being a more 
tough and costly metal, is rolled much thinner, and is designated 
by the number of ounces in a square foot; six ounce copper is very 
thin, but from 8 to 10 ounces forms a good covering, and 12 to 16 
ounces is very stout. 

648. In covering large roofs or other surfaces with any of the 
sheet metals, the joints should never be soldered together, but 
certain risings are made at the edges of the plates, and one plate 
is made to fold or lap over the projection of another in the man- 
ner of pa?ililes^ (501,) but in a much more close and perfect man- 
ner. Such joints are called laps, and if well executed will 
effectually prevent the passage of rain water. If the joints were 
soldered so as to render the whole one connected plate, the ex- 
pansion that occurs in hot weather would cause the metal to 
cockle up, loose its original flat surface, and perhaps form hollows 
that might retain water above the level of the laps, and cause 
the roof to leak. The contraction in cold seasons has an opposite 
effect, and causes one part of the covering to tear or break away 
from another, thus producing cracks that destroy the continuity 
of the covering. Laps should therefore be always so constructed 
as to allow of expansion and contraction, and as these laps are 
never very distant from each other, the quantity of allowance 



OP TIN PLATES. 367 

need be but very small. The plan for covering roofs with sheet 
metal, for which Professor Bonnycastle of the University of Vir- 
ginia has obtained a patent, is very simple, excellent, and effec- 
tive, and provides amply for the effects of change of seasons. 

649. Sheet metals, particularly in forming gutters, are fre- 
quently nailed to the smooth boarding that is placed under them, 
for their support, and in order to prevent the nail hole suffering 
water to pass, the nail and hole are covered by a small patch of 
solder. This is called dotting. The use of nails in this manner 
requires some judgment and foresight, as to the effect that may 
be produced by expansion and contraction, because this very fre- 
quently draws the nails when they are improperly placed, and 
produces worse evils than those they were intended to prevent. 

650. Tin Plates 

Soldered together are very extensively used in the northern 
cities of the United States, for making gutters, rain pipes, vallies 
of roofs, and even for covering buildings, but their cheapness is 
their only recommendation. Tin plates are merely very thin 
sheets of iron, coated on both sides with melted tin, so as to pro- 
tect the iron from rusting. But as the covering is not always 
perfect, and the iron must be exposed at the edges of each plate, 
if cut, it very soon becomes rusty, and is of short duration*, unless 
protected by frequent painting. It is a very convenient material 
for temporary purposes, but one that cannot be recommended 
where duration is desired. 

All the other metals are useless to the Builder or Engineer on 
account of their costliness or want of strength and durabihty, and 
therefore need not be noticed. 

651. The following tables of the average weight of square, flat, 
and round, or bolt iron, will be very useful to the Engineer in 
making his estimates of work to be executed, and in determining 
the weight or value of what is already done. The weights are 
given for pieces each ten feet long, which is better than giving the 
weight of single feet. A single foot in many sizes would require 
long fractions, and would after all be subject to error when ex- 
panded into large quantities from the smallness of the unit. Ten 
feet is less liable to this objection, and the weight of a single foot, 
or indeed of any quantity however small may be obtained from 
the tables, by taking the tenth part of the weights there given, or 
by dividing any weight by a quantity that has the same relative 
proportion to ten feet, as the quantity required to be known. 



368 



ON BUILDING MATERIALS. 



652. Table of the average weight of bars of flat Iron, each 

\Ofeet long. 



Inches. 


cwt. qrs. lbs. 


Inches 


I'cwt. 


qrs. lbs 


Inches. 


cwt. qrs. 


lbs. 


6 


X 


3 


1 : 1 : 15 


s^ 


X 


10 : 


3 : 12 


21 


X 


1 


: 1 


: 23 






1 


1 : : IS 






1 


: 


2 : 24 






1 

2 


: 1 


: 10 






1 

2 


0:3: 19 






1 

2 


: 


2 : 8 






3 

8 


: 1 


: 1 


5h 


X 


3 

4 


1:1:1 






f 


: 


1 : 20 


21- 


X 


3 


: 2 


: 2 






f 


1:0: 6 


Si 


X 


3 

4 


: 


3 : 5 






1 


: 1 


: 18 






1 
a 


: 3 : 10 






f 


: 


2 : 18 






9 


: 1 


: 14 


5 


X 


3 

3 


1 : : 13 






1 

2 


: 


2 : 4 






1 

s 


0:1. 


: 9 






5 
8 


: 3 : 23 






f 


: 


1 : 16 






3 
8 


0:1. 


' 






1 


0:3:2 


31 


X 


3 


: 


2 : 27 


2 


X 


3 
4 


0:1: 


• 24 


41 


X 


3 

4 


1 : : 10 






f 


: 


2 : 14 






1 


: 1 


: 15 






1 


: 3 : 19 






1 
2 


: 


1 : 27 






9 


: 1 


: 11 






1 

e 


: 2 : 25 






3 
8 


: 


1 : 14 






1 
2 


: 1 


: 6 






3 

8 


0:2:5 


3 


X 


3 
4 


: 


2 : 22 






§ 


: 


: 26 


41 


X 


3 


1:0:4 






f 


: 


2 : 8 


If 


X 


3 


0:1: 


20 






i 


: 3 : 13 






1 

2 


: 


1 : 23 






5 
8 


: 1 


: 12 






1 

a 

3 

8 


: 2 : 21 
: 2 : 11 


21 


X 


3 

8 

3 


: 
: 


1 : 10 

2 : 14 






9 
16 

1 
2 


: 1 
: 1 


: 9 

: 5 


41 


X 


3 


: 3 : 25 






1 


: 


2 : 2 






3 

8 


0:0: 


24 






1 


0:3:7 






1 
2 


: 


1 : 20 


11 


X 


3 


0:1: 


17 






1 

2 


: 2 : 17 






3 

8 


: 


1 : 7 






5 

8 


0:1; 


• 10 






3 
8 


0:2:0 


2i 


X 


3 

4 


: 


2 : 8 






9 
T6 


: 1 


: 5 


4 


X 


3 


: 3 : 19 






f 


: 


1 : 25 






1 
2 


0:1: 


2 






5 
8 


0:3: 1 






1 
2 


: 


1 : 15 






f 


0:0: 


23 






1 
2 


: 2 : 12 






3 

8 


: 


1 : 4 


H 


X 


3 

4 


0:1: 


11 






3 
8 


: 1 : 24 


2i 


X 


3 


: 


2 : 5 






9 

2 


0:1. 
0:1: 
0:0. 


: 3 

• 

• 22 



653. Table of the average weight of ten feet in length of 

square bars of Iron. 



Inches square. 


cwt. 


qrs. lbs. 


Inches square. 


cwt. qrs. lbs. 


3 


2 : 


.3:0 


11 


0:3: 2 


2i 


2 : 


.2:3 


\\ 


: 2 : 21 


2| 


2 


: 1 : 8 


If 


: 2 : 11 


2f 


2 


: : 11 


u 


: 1 : 25 


21 




: 3 : 18 


u 


: 1 : 15 


n 




2 : 24 


1 


0:1:6 


n 




: 2 : 5 


7 

8 


: : 26 


2i 




1 : 14 


1 


: : 19 


2 




: : 25 




: : 13 


If 




: : 8 


I 

2 


0:0:8 


1| 





: 3 : 21 







OP KODS AND WIRES. 



369 



All square iron less than half inch on a side is called nail rod^ 
and such iron is sold in bundles of about 5 feet long, each bundle 
containing about a hundred weight of such rods. 

654. »/^ Table of the average weight of ten feet of bolt or 

round Iron. 



Inches diameter. 


cwt. qrs. lbs. 


Inches diameter. 


cwt. qrs. lbs. 


3 


2 : : 18 


Jl 


: 2 : ]6 


21 


1 : 3 : 22 


u 


0:2:3 


21 


1:3:6 


If 


: 1 : 24 


21 


1 : 2 : 17 


li 


: 1 : 14 


2^ 


1 : 1 : 23 


n 


0:1:5 


2f 


1 : 1 : 11 


1 


: : 27" 


21 


1 : : 24 


7 

8 


: : 20 


2i 


1:0: 9 


3 
4 


0:0: 14,7 


2 


: 3 : 24 


1 


: : 10 2 


\l 


0:3: 9 


1 

a 


0:0: 6.54 


n 


: 2 : 26 


3 

8 


0:0: 3.68 



^b^. All cylindrical pieces of metal, whether iron, steel, brass, 
copper, &c., less than fths of an inch in diameter, are called wires; 
and wires are measured and described by passing them into a 
tool called a wire gauge. It consists of a thin flat plate of hard- 
ened steel, having a number of indentations made along its edges, 
all diminishing in size from the largest, and numbered in regular 
succession, so that whichever indentation a wire fits into, the 
number corresponding to it is the number of that wire. The 
wire gauge is an expensive tool, because it requires to be made 
with great care, since the gauges of different places and even of 
different countries, should be all exactly alike; consequently, 
naming the number of any wire to a distant correspondent, in- 
forms him the size of that wire if he possesses a similar gauge. 
The thickness of plate or sheet metals, is also designated and 
described by the numbers of this same gauge. The indentation 
No. 1, should be f^ths of an inch wide, or would measure a wire 
of that diameter, or plate of that thickness. No. 6 is ^Vhs wide, 
No. 13 3-Vth, No. 19 2Vth, No. 24 the -^-^^h of an inch, and so on. 

656. As iron chains are frequently used by Engineers for 
various purposes, the following table of their weights is given. 
47 



370 



ON THE DURABILITY OP MATERIALS. 



Ji Table showing the weight of one yard of close or short linked 
crane chain made from the best wrought iron. 



Diameter of the round 
iron of which the links . 
are formed taken in in-^ 
ches. 



i inch, 


3| lbs. 


• 


" 


3 

5 


4^ 


c 


■i|- inch, 27 lbs 


7 
16 


6^ 




1 32 


9 


8 
10 




\\ 41 


1 


12 




li 50 


3 


16 


i 


If 62 


7 

L 5 


23 


3 


iM 



CHAPTER IX. 



ON THE DURABILITY AND STRENGTH OF MATERIALS. 



Section I. — Of the Durability of Materials. 

657. Having in the fornner chapter given as full an account as 
our limits would admit, of the various materials that are used for 
the purposes of building and constructing machinery, the next 
object of enquiry must be into their durability and strength, and 
how these qualities may be affected by their position in the work; 
for until some knowledge is obtained of these points the Engineer 
would not know how to select or use his materials to the greatest 
advantage. 

658. The durability of materials can only be known by trial 
and experience, from which general deductions may be made. 
Thus it becomes known that a pine post, fixed in the ground, will 
soon rot and decay, while one of good swamp cedar will be of 
considerable duration; and of course the first material should never 
be selected for use, if the second, or one equally good, can be ob- 
tained. Again, experience teaches us, that some kinds of stone and 
brick are almost imperishable, whether they are placed under 
ground or exposed to the vicissitudes of the atmosphere; while 
others will moulder away and crumble to dust, or will break oflf 



ON THE DURABILITY OP MATERIALS. 371 

in splinters if exposed to frost. Of course, therefore, the latter 
classes should not be used, except for internal work, or such as is 
protected from weather. 

659. It is impossible to lay down rules that shall be applicable 
to all cases, as it must be that knowledge which the Engineer or 
builder can only acquire from experience, that must guide him in 
the selection and disposition of his materials. The following ob- 
servations and remarks on these heads may, however, prove useful. 

660. The principal agents of nature in carrying on the work 
of destruction, are heat, ivater or humidity, frost, wind, and electri' 
city; of course the action of all these should be guarded against as 
far as possible. 

661. Heat has a twofold operation; first, in producing actual 
conflagration or the consumption of constructions by fire; and 
secondly, in expanding the dimensions of all things; thereby alter- 
ing their figure or shape, and making them perfectly dry, by the 
evaporation of the natural juices or other humidity they may con- 
tain; thus causing them to be more absorbent than they otherwise 
would be. This latter effect does not require the presence of ar- 
tificial fire, but is daily going on, under the sun's influence; and as 
cold contracts all things, so the natural change of temperature 
that occurs daily, or at any rate annually, is constantly altering 
the dimensions of things. 

662. The first eflfect of fire, makes it necessary for the Engineer 
and Builder to be very careful in the direction and construction 
of all flues or chimneys of fire places, and to guard against their 
coming into contact with any timber used in the roof or other 
parts of the building; and of course no timber or combustible mat- 
ter of any kind should be let into, or be supported by a chimney, 
or be placed so near to it as to be endangered by the heat. In 
London the ravages of fire are to a certain extent guarded against 
by legislative interference; for an act of parliament, called the 
buildifig act, was passed in 1774, which not only regulates the 
thickness and strength of walls, but contains many wholesome pre- 
cautionary regulations against fire; and an act having similar 
objects, though less extensive in its range, was passed in Boston, 
Mass., in 1818. These acts prohibit the erection of wooden frame 
buildings in the respective cities, except in a few particular cases 
comprehended in very narrow limits, and require that all future 
erections shall be in brick, stone, or other uninflammable material; 
that all roofs shall be covered with slates, tiles, or metal, and 
nothing inflammable be used upon them, and that brick partitions 
shall be formed between every house, and shall extend above their 
respective roofs, so that no one roof may have communication with 
another. The London art goes still further, because it ordains 



372 ON THE DURABILITY OF MATERIALS. 

that all flues or fire places shall be made in the party or partition 
walls; and that no hole or open connnriunication shall be left or 
nnade through such walls, nor shall any timbers be inserted into 
them, unless the ends of such timber are covered with a quantity 
of brickwork sufficient in thickness to prevent the transmission of 
heat; consequently nothing but girders are so used, and all joists 
and rafters run from back to front, or parallel to the walls of par- 
tition. The consequence of which is, that if one house takes tire, 
there is little or no opportunity afforded for its communication 
with those that adjoin it. In the modern houses of Philadelphia, 
where it is believed no such regulations exist, partition walls of 
brick are also used; but if several houses are on the same estate, 
or built by the same person, it is no uncommon thing to find the 
floor joists running through the party walls, and extending from 
one house to another; and to see roofs covered with shingles of 
wood, passing in a uniform line over several houses, and over the 
partition walls, so as to establish a free communication for fire 
between one house and another. To prevent the passage of fire 
between the bricks of a chimney, in case of its taking fire, the 
joints of such brickwork ought always to be laid close and full of 
mortar, and the inside of the flue should be pargetted, which is the 
technical name applied to plastering within a chimney. This 
effectually stops up all crevices or openings through which sparks 
or flame could pass, and renders the inside of the flue more smooth 
and even for the passage of the smoke. 

663. The expansion and contraction of materials by heat and 
cold, is a natural effect that cannot be guarded against, except 
when circumstances admit of the materials that are most subject 
to it being covered by brick, stone, wood, or other bad conduc- 
tors of heat, or such as transmit it slowly or imperfectly; in which 
case they will be much less affected. Those substances that con- 
duct heat most rapidly, are also those that are most subject to 
expansion and contraction; consequently, this effect does not pre- 
vail to any sensible or detrimental extent in stones, bricks, mortar 
and the earths; but it is quite perceptible, and requires to be 
guarded against in the metals, particularly when used in a long 
continuous length, as in the construction of iron bridges, or lay- 
ing iron pipes for conveying water long distances; for notwith- 
standing the effect may be too small to be seen in a single pipe 
of 9 feet long, yet, if the line of pipes extend 500"yards, and it 
takes place simultaneously in all of them, the sum of all the 
actions is frequently such as to open a joint, or even tear a per- 
fect pipe asunder. Several instances have come under the eye 
of the writer, in which strong bars of wrought iron, not exceed- 
ing 6 feet in length, have been let into stone walls at their oppo- 



ON THE DURABILITY OF MATERIALS. 373 

site ends, and then run in with lead to produce perfect stability 
and firmness, and yet one or both the joints so made have be- 
come loose, and torn out, and the stone near the lead shivered 
away, as if it had been struck by a hammer. Metals alone are, 
however, subject to this inconvenience. 

664. Another species of expansion and contraction frequently 
occurs in bodies that are not metallic, arising from their hygro- 
metrical properties when damp and dry; and this belongs more 
especially to some varieties of wood. Wood is not subject to 
any material alteration in the length of its tibres from this cause, 
but it operates very perceptibly in the opposite direction. Wood 
and most vegetable substances, always shrink to a certain extent 
by drying, and swell or expand to their former dimensions, or 
nearly so, when wet or humid. This propert}'' gives tightness to 
casks, vats, or tubs for holding water, and it causes the boards 
used in floors, doors or joinery work, to expand and become tight 
and close in damp weather, or to shrink when dry. This effect 
in vegetable matter diminishes with age, and its prevention is 
one of the uses of seasoning timber, and keeping it a long time 
before it is used. 

665. Water, or rather humidity, is the great and general cause 
of decay in materials. It acts as a solvent, if the substance 
contains any thing that is soluble; and in this way, or by the 
motion of water, parts of the material are abstracted and carried 
away. It also acts chemically in producing fermentation, decom- 
position, or decay, commonly called rotting; and it encourages 
and promotes the production of certain Jicngi or paricidical plants 
which destroy the texture and hasten decay. Notwithstanding 
this character has been given to water, it belongs more properly 
to water and air conjoined; for neither of them act powerfully, or 
rapidly, when separate. Thus a piece of sound timber, or a bar 
of iron, if exposed to the free action of air that is perfectly dry, 
will endure for ages without symptoms of decay: of which the 
present roof of Westminster Hall, London, the largest room in 
Europe, is a fine example. It is wholly of black chestnut, un- 
painted or protected, and is in perfect repair, although erected in 
1397, by Richard II. Being a gothic structure, it is unincum- 
bered with a ceiling, and open to full view as well as to the action 
of the air within the building. Timber and iron will also endure 
an immense time, if constantly and wholly covered by water; 
for on taking down the old London bridge in 1830, when the 
present new bridge was completed and opened, most of the piles 
of the old bridge erected between 1176 and liiOO, were found as 
sound as new timber, and much harder. But if timber or iron 
are occasionally wet and dry, the first will decay in a few years, 



374 ON THE DURABILITY OF MATERIALS. 

and the latter will speedily contract rust, which gradually eats 
into it, until its whole substance is destroyed. The more rapidly 
a substance can become dry after it has been wetted, the less 
likely it will be to be affected by decay; hence, whenever hu- 
midity is retained, it never fails to operate prejudiciously. 
Wooden, and even iron posts, always fail first near their bottoms, 
because the natural humidity of the ground, or even the moisture 
that may fall upon a horizontal floor or platform, assists in the 
operation. If a column of timber is faced or ornamented with 
a plinth or moundings nailed upon its outside, and water can get 
into thejoints between them, decay will take place there, although 
the upper part, that is fully exposed to the air, may be quite 
sound. This decay is produced by the effect of capillary attrac- 
tion, retaining the water or humidity that is introduced and 
absorbed, thus permitting it much longer time for its operation 
than if it dried away, which it would have done, if open; for the 
same reason the sills of wooden buildings, the feet of rafters, and 
tenons fitting into mortice holes, always decay sooner than the 
parts that are exposed to the full action of open air. 

666. The sun's heat by drying and expanding timber, causes 
it to become much more absorbent of water than it otherwise 
would be, and if the water so absorbed, is not permitted to escape 
freely, it never fails to produce decay. The great object to be 
attained by painting external wood with oil colours, is, therefore, 
preservation more than ornament, for if the paint is good, it 
ought, when dry, to form a coat or casing that is impervious to 
water, or even humidity, and when that is the case its preserva- 
tive powers are well known. For this reason paint should never 
be applied to work that is in a humid state, not only because it 
will not adhere with certainty, but because it incloses and shuts 
in the moisture. 

667. The detrimental effects of humidity not only apply to 
wood work, but extend to bricks, stones, and all things that are 
absorbent, especially if they are at all soluble at the same time; 
but the worst consequences ensue from the exercise of frost upon 
bodies that contain moisture; for water in freezing crystallizes, 
and occupies more bulk than in the fluid state; and the force with 
which the expansion takes place, is so great, as to be capable of 
bursting the strongest water pipes, lifting portions of walls, and 
disturbing the state and condition of the heaviest bodies. If, 
therefore, brickwork, masonry, earthwork, or even timber that 
is absorbent, happens to be attacked by frost while full of hu- 
midity, it is frequently so burst or shaken by its effects, that if 
it does not fail immediately, it becomes so loosened and detached 
as to give way afterwards to the smallest force, or at any rate its 



ON THE DURABILITY OP MATERIALS. 375 

surface becomes more disposed to rapid decay. Many varieties 
of brick and stone, that is, such as absorb moisture readily, and 
are tardy in parting with it again, ought therefore never to be 
selected for outside or foundation work. 

66S. The same reasoning explains why external brickwork 
and masonry, as well as plastering, should not be done in frosty 
weather; for if the water necessarily introduced into the mortar 
should freeze before the mortar sets, it will afterwards fall to 
powder, and never make a strong or adhesive joint. 

669. Nothing resists the effects of spontaneous decay more 
effectually than charcoal, and it is on this account that the bot- 
toms of wooden posts are frequently burnt before inserting them 
in the ground. The error generally committed is in not burn- 
ing the surface of the wood to a sufficient depth; because when 
advantage is to be taken of the preservative quality of charcoal, 
it ought to have a considerable thickness. 

670. The salt of mercury, called corrosive sublimate, {bichlo- 
ride of mercury,) has a wonderful power in resisting decay, as 
well as in preventing the occurrence of dry rot, one of the 
greatest enemies the builder in wood has to contend with. On 
this account this salt is now extensively used in ship building, 
and it is believed that its adoption will be attended with very 
beneficial consequences. Corrosive sublimate is a strong poison, 
and therefore requires great care and circumspection in its use. 
One pound of the salt is dissolved in five gallons of water, or in 
that proportion; and this lye or pickle being made in a brick or 
other close tank, the timber intended to be preserved is soaked 
in it until it becomes fully saturated, when it is taken out, dried 
in the air, and may be used. 

671. The dry rot is a disease that attacks converted timber, 
but which seldom makes its appearance unless that timber is put 
in a damp situation, or is deprived of free access of air. It is 
therefore of common occurrence in the ends of joists or girders, 
that are let into walls, or in wainscotting applied against a damp 
wall, and is very common in ships which consist of strong ribs 
boarded on both sides, so as to confine air and humidity between 
them. Although humidity seems necessary to the production of 
dry rot, yet its effects and appearances are quite different from 
those of rotting by water. In general, it causes the surface of 
the wood to swell up in an appearance like blisters, with cracks 
between one blister and another, but without any appearance of 
humidity; and the wood not only looses all strength, but will 
crumble to a brown dust or powder on the smallest touch. The 
colour of the wood is always much darkened by dry rot, and it 
acquires a smell similar to that of mushrooms. Dry rot has the 



376 ON THE DURABILITY OF MATERIALS. 

singular property of spreading very rapidly after once making its 
appearance, thus communicating the contagion to neighbouring 
timber that otherwise would not be affected. It is also capable 
of propagation, since if a piece of wood infected with dry rot, is 
carried to a distant place, and put in contact with wood that is 
damp, it will frequently produce the disease. Of course, there- 
fore, whenever dry rot is discovered, no time should be lost in cut- 
ting away and removing the infected parts, taking care at the 
same time to expose those left to as free a circulation of air, or other 
drying process, as possible. It was formerly supposed that dry rot 
was produced by using timber too soon after it was cut, and which 
therefore contained the natural juices of the tree which dissipate 
by seasoning; and there is no doubt but this description of timber, 
if it does not produce, encourages the disease, which is now clearly 
proved to be produced by a parasitic plant of the fungus or mush- 
room tribe {boletus lachramans) that grows upon the wood, and 
exhausts it of all its substance and strength. This plant requires 
a certain degree of moisture for its production and maintenance, 
which accounts for its only occurring in damp situations. It has 
not the shape or appearance of the common fungi, but sends forth 
long and extended branches of considerable tenacity, very much 
resembling some of the fine branched sea-weeds when spread upon 
a board or paper; and these ramifications, which are of a brown 
colour, adhere strongly to the wood, but never rise or branch be- 
yond its surface, and frequently assume a beautiful appearance, 
though the strength of the wood is rapidly destroyed wherever 
these rapacious branches attach themselves. Dryness, whether 
produced by heat or evaporation, assisted by a free circulation of 
air, destroys the plant, or even prevents its appearance, and these 
are therefore amongst the best remedies that can be applied for 
the prevention or cure of this enemy to timber work. Any thing 
likewise that destroys the vegetative power of the wood, will also 
remove the liability to this disorder, and accordingly steeping wood 
in hot tar, or in strong brine of salt and water,, or of those salts 
called vitriols, have been resorted to; but recent experiments that 
have been made in the British navy yard at Deptford, near Lon- 
don, prove decisively that nothing yet tried is so efficacious as the 
solution of corrosive sublimate before referred to, since timber pre- 
pared with that material, and placed in damp vaults, in contact 
with the most vigorous dry rot, and under the most favourable 
circumstances for contracting it, was not affected in the slightest 
degree. 

672. The effects of wind can only be guarded against by 
strength, and the adoption of such forms as will not present flat 
sides for the wind to act upon. On this account the round or 



ON THE DURABILITY OF MATERIALS. 377 

cylindrical shaft of a column, will have a much better chance of 
standing against a high wind than a square shaft or chimney ex- 
posing the same surface; because in whatever direction the wind 
comes against a cylinder, it is always met by a round surface 
which divides it, and presents an oblique action. Had the shaft 
been square, and the wind blowing perpendicular to any one of 
its sides, its power would be much greater, although it would be 
still further diminished when blowing against one of its angles. 
On this account the spires of churches are never made in the form 
of square pyramids, but are polygonal, and would be stronger, 
though less handsome, if round. But light-houses for navigation, 
where strength is more important than beauty, are made circular 
and tapering towards the top. The effects of wind ought always 
to be guarded against in every erection, with the same care as 
weight or any other force; for if this is not attended to, the whole 
may be unexpectedly destroyed. One of the chief objects of 
bracing in carpenter's w^ork, to be hereafter spoken of, is to resist 
the action of wind. 

673. Electricity has a double action, sometimes showing itself 
in the powerful and tremendous form of lightning; and constantly 
operating to produce the decomposition and decay of things by the 
slow and unperceived influence of galvanic action. Lightning can 
only be guarded against by the erection of proper conducting rods 
of iron or copper, which should extend above the highest part of 
the building and pass downwards, without any break or intermis- 
sion to the ground, which they should enter and pass into, to a depth 
of several feet below the lowest part of the foundation of the 
building, or at any rate should penetrate the earth until they meet 
with constant humiditv in all seasons: because moist earth is a 
good conductor of electricity, and readily permits its escape. Con- 
ductors, or lightning rods, should be of such magnitude as will in- 
sure their carrying off the whole quantity of electricity without 
melting; and as may insure their not wasting rapidly by rust or 
oxidation. No rod of iron less than f of an inch in diameter, 
should be used, but an inch will be better. Both the upper and 
lower ends should terminate in sharp points, because electricity 
is known to enter and to leave points with less violence than any 
other shape; and as the upper point, from its constant exposure to 
all weathers, soon decays, and is sometimes melted by a stroke of 
lightning, it is best to protect it by forming it of some good con- 
ducting substance that is nearly imperishable, and charcoal, solid 
plumbago or hlack-leadj and the metal platinum, are best suited to 
this purpose, the last being the best; and as the quantity of pla- 
tinum is not necessarily large, the expense is not great. As light- 
ning rods cannot be procured of sutlicient length in one piece, the 
48 



378 ON THE DURABILITY OP MATERIALS. 

separate rods ought to be welded together if of iron, or one length 
may be screwed into another, which method is usually adopted 
with copper rods: and when they are made of iron, (that metal 
being usually selected on account of its cheapness,) the lower ter- 
mination, and about three or four feet above the ground should 
be made of copper, to prevent the decay and dangerous conse- 
quences that might attend the lower end being rusted away and 
deficient. Perfect continuity of the metallic rod is of the highest 
importance; for lightning never does damage, except when it strikes 
an imperfect conductor, or has to jump or pass from one conduct- 
ing substance to another. If a building is unprotected by a metal 
rod, and happens to be struck by a flash, it is generally found that 
the lightning first strikes and melts any lead, copper, iron, or other 
metal that is in the roof, even to the nails; from thence it finds its 
way to bell wires, the silvering of looking-glass, fire grates, locks, 
bolts, hinges, or other articles of metal that may be distributed 
about the place, and if these are separated by dry timber, brick 
or stone work, through which the lightning must force its w^ay, it 
never fails to break them asunder or shatter them to pieces, be- 
cause it is in the effort to get from one conductor to another that 
it exerts its violence. 

674. It has long been known, that where wrought iron railing 
or other work was fixed to stone-work, by letting the iron into the 
stone, and filling up the vacuity with melted lead, the iron would 
decay much more rapidly in the open air near the lead than in 
any other part. Likewise that ships fastened together by iron 
bolts could not be sheathed with copper, on account of the rapid 
decay of such bolts; consequently, all vessels intended to be cop- 
pered, are fastened with copper bolts. No one suspected this to 
be an electrical effect, until the late researches into galvanism 
laid open the fact, that whenever two metals possessing difTerent 
susceptibilities of oxidation, were placed in contact with each 
other, and with water or any saline solution at the same time, the 
most oxidable metal would soon be dissolved and disappear. Ships 
are sheathed with copper to protect the wood from an aquatic 
insect that bores into and destroys it, but which cannot penetrate 
the metal. The copper is however acted upon by the friction 
and salt of the sea water, which corrodes and partially destroys 
it, so that it soon wants repair, if not renewal. 

Sir Humphrey Davy most ingeniously applied this electrical 
principle to the preservation of ship coppering, by soldering a small 
plate of zinc to each sheet of copper; and as zinc is the most 
readily oxidized, he expected that the salt sea water would act 
upon the zinc in preference to the copper, which would thereby 
be preserved at the expense of a small quantity of the much less 



ON THE DURABILITY OP MATERIALS. 379 

expensive zinc. The trial of the experinnent on a large scale, 
fully corroborated the truth of his views; for the copper was kept 
quite clean and free from oxidation as long as the zinc lasted; not- 
withstanding which this beautiful exemplification of the induc- 
tions of science to the useful purposes of life failed from a cause 
Davy had never contemplated. When copper is used in the ordi- 
nary way without protection, its surface becomes green from the 
oxide and muriate of copper, and other salts that form upon it, 
and these salts being acrid and poisonous, prevent shell fish and 
other marine animals, from attaching themselves to the copper, or 
even approaching it. But when the copper was kept clean and 
free from oxide by the zinc preservers, there was no longer any 
thing poisonous about it, and it was found that oysters, limpets, 
barnacles, and other crustaceous marine animals attached them- 
selves to the copper at the bottom of the vessels in such quantity, 
as to efifect the rapidity of their sailing; and they adhered so close- 
ly, that they could not be knocked off without injury to the cop- 
per. Any one acquainted with the nature of sailing vessels, knows 
that a great part of their perfection consists in having a perfectly 
clean, smooth and uninterrupted surface next the water, and on 
this account alone the mode of preserving copper on Sir H. Davy's 
principle, has of necessity been abandoned. 

675. Iron is painted with oil paint, to preserve it from the effects 
of weather, and the base or body of such paint is usually white 
lead, or carbonate of protoxide of lead reduced to powder and 
ground with linseed oil. Recent experiments that have been made, 
seem to prove that even the oxide of one metal is not a proper 
protecting cover for another, on account of a galvanic decompo- 
sition, similar to that above referred to, being brought about; and 
that the earths, such as the ochres and boles, sulphate of baryta, 
and animal charcoal or ivory black, are much better calculated 
for insuring duration. Asphaltum, which is a black and very in- 
soluble bituminous substance, also makes a good and permanent 
covering for iron in the nature of a japan or varnish, as it dries 
with a fine gloss. 

676. As the great enemy to the durability of materials is hu- 
midity, and their being permitted to be occasionally wet and dry, 
so of course every thing that tends to prevent this effect taking 
place will promote durability. For this reason all wood and iron 
or other metal work, especially such as is exposed to the constant 
action of the atmosphere, should be thickly painted with oil colour, 
or should be covered with pitch, tar, or something that is capable 
of resisting atmospheric action. All roofs and walls should be 
made as smooth as possible, and all projections and cavities that 
may catch and retain water, should be avoided. 



380 ON THE ABSOLUTK STRENGTH OF MATERIALS. 

677. Although pointing a wall, which is scraping out the old 
mortar from its joints, after it begins to decay, and filling the cavi- 
ties afterwards with new mortar that will become hard, adds but 
little to the strength of a wall, yet it adds much to its duration. 
For old and decayed mortar is porous and so absorbent, that it 
retains humidity a long time, and the exposed upper edges of 
bricks and stones catch and retain water, which soaks into the 
wall, and the use of pointing is to fill up all these cavities, and 
produce a uniformly smooth surface, upon w^iich water will run 
down. For the same reason all large timbers exposed to the open 
air, should have their upper sides worked into a saddle hack fornix 
that is, should be angular upwards like a roof, to such an extent 
as will prevent water lodging upon them, as it would do if the 
upper side was a horizontal plane. 

Section II. — Of the absolute strength of materials. 

678. By absolute strength, w-e are to understand, the resistance 
which any body whatever is capable of offering against change 
of form, as in stretching, or against actual fracture or breaking 
when it is subjected to the action of a direct and known force, ope- 
rating in a right lined direction. 

679. This subject naturally divides itself into three heads for 
consideration, viz: 1st. The weight or load which any body is ca- 
pable of sustaining without crushing or breaking to pieces; 2ndly, 
the weight or load which a material is capable of supporting 
when that load is appended to, or suspended by it: 3dly, the 
force of torsion or twisting, or the force that will be necessary to 
twist or break a bar, fixed at one end, while the force is applied 
to the other as a tangent to a circle supposed to be produced 
perpendicular to the axis of the bar, and having that axis as a 
centre. 

These are cases that occur constantly in the Engineer's prac- 
tice, and may be illustrated by the following examples. 

680. 1st. Suppose a stone pillar or column has to be erected: 
the building of it of course, commences from the bottom, and the 
stones that are to form the base or foundation, must be first put 
in their places. Layers or courses of stone are placed one above 
the other in succession upon this base, and each additional course 
of stones is an additional load which the base has to bear. Now 
we may consider these courses of stone to be piled one upon the 
other, until at last the weight becomes so enormous, that the stones 
in the base are unable to support it, and of course they will crush 
or crumble to pieces; the basement being thus destroyed, the 
whole fabric no longer retaining its perpendicular position must 



ON THE ABSOLUTE STRENGTH OF MATERIALS. 381 

fall. It is, therefore, quite necessary that the Engineer or Builder 
should possess some rule by which he may apportion the strength 
of his basement to the load that he intends placing upon it, for this 
principle not only applies to the column that has been chosen as 
an example, but more particularly to the piers of bridges in which 
the upper part of the load increases in a much more rapid ratio 
than in a column, and it applies even to every column, pier, wall, 
and house that may be built, in all which cases the weight of the 
material employed must be added to the load it is intended to 
support. 

681. 2nd. Every weight that is lifted from the ground by a 
rope or chain affords an example of the second head, and this is 
an operation that is constantly going on; for all heavy stones, or 
pieces of machinery that have to be placed in elevated positions, 
are sq raised by pullies and ropes (technically called blocks and a 
fall), and if the Engineer had not some data to work upon, no con- 
fidence could be placed in any rope or chain, since it might break, 
and destroy the piece before it had reached its destination, besides 
endangering the lives of those employed below in the act of rais- 
ing it. When the load has to be moved a great distance, the 
weight of the rope itself forms an element in the calculation, and 
must be added to the load that has to be sustained and lifted; and 
in mining operations, when the perpendicular shaft or pit is deep, 
this weight is of material consequence. Thus in the celebrated 
silver mine of Valenciana, at Guanaxuato, in Mexico, the princi- 
pal shaft is 640 varas deep, (33 English inches to the vara,) and 
this is worked by flat ropes 4 inches wide, every vara of which 
weighs rather more than 5 pounds; consequently when this rope is 
extended or let down the shaft, the upper end of it, together with 
the cylinder to which it is attached, has to bear its own weight 
of about 3200 pounds, or rather better than a ton and a half, in- 
dependent of any load that may be attached to its lower end, and 
which is usually about one ton more; so that the weight of the 
rope in this case exceeds that of the load it has to support. The 
force of extension not only applies to raising loads, but to support- 
ing them in a quiescent state, as in roofs and suspension bridges, 
where the whole weight of the platform or roadway, and all loads 
that pass over it, is hung up to, and supported by chains or rods 
of iron properly arranged for the purpose. Galleries, and even 
rooms, are sometimes supported in this way from the roofs of build- 
ings which inclose them. The power of adhesion of nails, glue 
and cement, are likewise generally considered under this head. 

682. 3d. The third head is of constant occurrence in all mill- 
work in which cog wheels are introduced. A rotary motion is 
produced in the first instance by the action of a steam-engine, a 



382 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

water-wheel, or some power; and this has to be communicated to 
the place of operation either immediately, or by the intervention 
of wheels, which in either case must be supported by long bars 
with pivots or gudgeons on their ends, and which are called shafts 
or journals. If the power of the first mover is not sufficiently 
great to impel the machinery at the opposite end of the shaft, then 
the shaft will be incapable of revolving, and will be set fast; con- 
sequently, the whole power of such first mover will be expended 
in an etfort to twist and break off the shaft, because it cannot 
move. Or if it does move, and the machine is strong enough in all 
its parts to perform well, since the motion and power are always 
communicated through the shaft, that shaft while moving will 
always be subject to a force equal to the power of the machine 
to twist and break it oflT, and must consequently have strength 
sufficient to resist this action. 

683. The only knowledge to be acquired on these several points 
is derived from experience alone, and can derive little or no bene- 
fit from science; because the strength that is called into action in 
all these cases, depends alone on the cohesion or tenacity and 
rigidity of the material employed. All, therefore, that science 
can do to aid the practical Engineer, is to select proper materials; 
to try the amount of their cohesive force or strength by the most 
approved methods; and to record the results of the experiments 
faithfully and impartially, accompanied by such an account of the 
material as may prove its identity, stating at the same time the 
temperature and other circumstances under which the experiment 
was tried. If for instance a bar of iron or a rope of hemp of a 
certain size, were found capable of sustaining a certain weight 
before they broke under the experiment, it is but fair to infer 
that another similar bar of iron or rope, would bear an equal 
weight or strain at any future time or place; and by loading it 
with a weight considerably under that which produced fracture, 
we should have a confidence in its stability, which may fairly be 
said to be in the proportion of the weight placed upon it, with that 
which was known to produce its fracture. 

684. All therefore that can be done to assist the student in this 
part of the subject, is to place before him the results of such ex- 
periments as have been accurately tried and recorded, and which 
may therefore be relied upon, accompanied by such observations 
as apply to the organic construction of the materials used; and 
being in possession of them, it will be for him to make experi- 
ments upon the materials he has to work with, in order to deter- 
mine whether they are more or less worthy of confidence than 
those taken as examples. 

685. In naming the forces brought into action, it is necessary to 



OF RESISTANCE TO PRESSURE. 383 

state that passive or quiescent and not concussive forces are al- 
ways understood. By passive force, is meant that the weight is 
either gradually accumulated, or very gently transferred to that 
which has to bear it, like the gradual building of a wall or a 
column, and is not discharged suddenly upon its bearing, so as to 
add moving impulse to its weight, because then its power would 
be much increased. A flint pebble may have a board placed over 
it, and that board may be gradually loaded with a ton of iron or 
other material, and yet the pebble will not break; but if that 
same load fell suddenly, and all at once upon it, or even if the 
pebble received a smart blow from a hamn^er not weighing more 
than two pounds, it would be shivered to pieces. Indeed the 
effect of a concussive force is so different from a quiescent one, 
and is attended with so many varying circumstances, that it is 
almost impossible to calculate the effect of the first with any thing 
like practical certainty. The same reasoning teaches us that 
rooms that are built for dancing, or for any manufacturing pur- 
pose, which is attended with sudden shocks, concussions, or vibra- 
tions, require to be made much stronger than what would be 
necessary for supporting the same weight applied in a passive 
manner. 

686. As the absolute strength of materials depends upon their 
cohesion and tenacity, so of course that strength will be governed 
in great measure by the quantity of material that is exposed to 
action, or will be as the area of the surface acted upon. Thus, 
if a cubic inch of stone is capable of resisting or supporting a cer- 
tain load or weight, two cubic inches should be capable of sup- 
porting twice as much; consequently, the strength is as the surface, 
or what is the same thing in most cases, as the square of the 
diameter. If, therefore, a block of one inch square, can support 
a certain load, one of two inches square should support four times 
as much, one of three inches square nine times as much, &c., and 
this applies not only to the force of compression, but of extension 
likewise, so that a small difference in diameter produces a great 
difference in supporting strength. 

6S7. We shall first examine some of 

The effects produced hy Pressure, 

a subject to which less attention has been paid by men of science, 
as well as of those of practice, than any of the other modifications 
of force applied to materials. This has probably arisen from the 
enormous pressure that most strong substances are capable of sus- 
taining before they crush or give way; a pressure so great as to 
induce many practical workmen to suppose, (though very impro- 



384 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

perly,) that their strength is infinite. Galileo was the first person 
who investigated this subject with any thing like rigorous exacti- 
tude, and he was followed by several men of eminence. But 
however plausible their investigations appeared to be, they were 
more theoretical than practical, as turned out in the sequel. For 
no sound practical results can be derived from a theory that is 
not founded upon careful and well directed experiments, which at 
that time had not been made. M. BufFon, the celebrated natu- 
ralist, was among the first who tried such experiments upon va- 
rious kinds of timber, and they are recorded in the annals of the 
Academy of Sciences at Paris, for the years 1740-41, and were 
on a scale sufficiently large to have afforded just conclusions, had 
he not omitted to ascertain the direct and absolute strength of the 
timber he employed. It may, however, be inferred from his ex- 
periments, that the strength of the ligneous fibre is nearly in pro- 
portion to the specific gravity of the wood. Muschenbroeck, whose 
accuracy entitled him to confidence, made a number of experi- 
ments on wood and iron, which, by being tried on various speci- 
mens of the same materials, aflTorded a mean result considerably 
higher than other previous authorities. The Royal Society of 
London likewise instituted some experiments on this subject among 
its earliest labours, and experiments were also tried and are re- 
corded by Marriotte, Varignon, Perronet, Ramus, and many other 
Engineers and Philosophers of France, and they were afterwards 
taken up again by VEcole Polytechnique, under the direction of 
M. Prony. But the investigations of Emmerson in his Mechanics, 
and the more recent experiments of Messrs. Telford, Rennie, 
Brown, and others, and the subsequent investigations of Drs. 
Thomas Young, Professor Robison, Messrs. Tredgold, Barlow, and 
Peter Nicholson, are deemed most accurate, and are therefore 
mostly relied upon, and generally quoted as authorities. Dr. 
Young has been most happy in his mode of investigating and illus- 
trating this subject, as detailed in his Lectures on Natural Philoso- 
phy, 2 vols. 4to., 1807; and this work and the- treatise on the 
Strength of Materials, written by Dr. John Robison, late Profes- 
sor of Natural Philosophy in the University of Edinburgh, for the 
Encyclopedia Brittanica, and republished after his death in 1805, 
with his other scientific papers, under the title of a System of Me- 
chanical Philosophy, revised and edited by the able hand of Dr. 
Brewster, may be said to contain the whole of what had been 
done, or was known of this interesting subject in all its ditferent 
bearings to their several dates. Since the publication of these 
books, additional experiments have been made, and new investi- 
gations taken by the late Mr. Thomas Tredgold, who has em- 
bodied all that is practically interesting and useful in respect to 



OF RESISTANCE TO PRESSURE. 385 

iron, in his valuable treatise on the strength of Cast Iron and other 
metals, with nunaerous tables and practical examples; and Mr. 
Peter Barlow has published a separate work, on the same princi- 
ple, respecting the strength and management of timber. Two 
works that are so replete with valuable information, that no Engi- 
neer should be without them, and the student of this profession is 
therefore referred to them for details which are beyond the scope 
of the present work to introduce. 

688. The experiments of Mr. George Rennie, Junr., above re- 
ferred to, were communicated to the Ro3^al Society of London, 
and are published in their Philosophical Transactions for 1818, 
Part L, and afterwards copied in the Philosophical Magazine, 
Vol. LIII. p. 173. These experiments were made with an accurate 
lever or steelyard machine constructed for the express purpose, 
and in which every care and precaution was used to prevent fric- 
tion and insure accuracy. The iron lever was ten feet long, and 
the pieces to be subjected to pressure, were placed five inches 
from the fulcrum or centre of motion. The pressure required to 
crush specimens of metal, was however so great, that Mr. Rennie 
was compelled to limit his experiments to very small pieces, which 
were reduced by the file to a perfect cubic form. They were 
placed between flat plates of hardened steel, above and below 
which were pieces of thick sole leather, by which means an equa- 
ble pressure was communicated to every part of the surface. 
The beam was balanced so that its own weight could not inter- 
fere with the accuracy of the experiments, and the pressure was 
brought into action by the most gentle means, so as to make the 
effect gradual, and to avoid any thing like a blow or concussion, 
and the following are some of the most useful results. 

689. A cube of good grey cast iron, each side of which was -|th 
of an inch, taken from the middle of a block, the specific gravity 
of which was 7.033, on the average of three experiments, required 
to crush it {Avoirdupois lbs.) 1439.66 

Another specimen of cast iron with specific gravity 
of 6.977 was tried in rectangular blocks of J by i inch, 
and the average of three experiments was their crushing 
with /k21l6. 

The following experiments show that the power of 
resisting a perpendicular pressure, is not in proportion to 
the horizontal surface, but is compounded of that and 
the attitude of the prism. Pieces ^th inch square of the 
same cast iron, were cut to different lengths, as stated 
below, when the resistance diminished with their in- 
creased height, but not in emy regular ratio. 
49 



386 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

A prism of J inch by l^ inch, yielded to lbs. 2005. 

I by I do. 1407. 

i byf do. 1743. 

I- . by| do. 1594. 

^ by I do. 1439. 

In four experiments with i: inch cubes taken from 
the middle of a block, having specific gravity 7.033, 
the average weight supported was 9773.5 

In four experiments on iron cast horizontally into bars, 
the specific gravity of which were 7.113, and reduced 
to J inch cubes, the average resistance vvas 10114. 

In five experiments made with ^ inch cubes taken out 
of the lower ends of similar bars cast vertically instead 
of horizontally, but having specific gravity of only 7.074, 
the average resistance was 11136.75 

Thus proving what has been before insisted on (618) that the 
strength of iron is improved by the heavy weight of the mass in fu- 
sion above it, although the specific gravity in this case does not 
show increased density. 

The above are only a very few of the many experiments that 
were tried on cast iron and other metals, for the details of which 
the reader is referred to Mr. Rennie's paper,* but the following 
experiments on other metals were also made, and may be useful. 
A quarter inch cube of cast copper crumbled with lbs. 7318 
Do. of fine yellow brass, would not crumble but was 
reduced one-tenth of its thickness by 3213/65., and to ^ 
its former thickness by 10304 

Do. of wrought copper did not crumble — was reduced 
yVth of its thickness by 3427 

and to l^th of its first thickness by 6440 

Do. of cast tin, was reduced y^g-th by 552lbs. nnd to 
^d by 966 

Do. of cast lead, was reduced to ^ its thickness by 483 

690. The following are among experiments that were also tried 
on miscellaneous substances. In these the pressure was communi- 
cated by a pyramid of steel, the base of which rested on the sub- 
stance, leather being interposed between them, and the lever 
pressed on the apex of the pyramid. 

A cubic inch of seasoned elm wood failed with lbs. 1284 

Do. of American pine 1606 

Do. of White Norway deal 1928 

Do. of English oak (mean of two trials) 3860 

* Philosophical Transactions of Royal Society for 1818, Part I., or the Philo- 
sophical Magazine, Vol. Llil. 



OF RESISTANCE TO PRESSURE. 387 

An inch cube of chalk crusted with lbs. 500 

An inch anJ half cube of pale burnt or soft brick 1265 

Do. of well burnt brick 1817 

Do. of hard paving bricks (3 trials) 2254 

Do. of sanne highly burnt 3243 

Do. of Stourbridge fire brick 3864 

Do. of redorferruginoussandstone(460) 7070 

Do. the like from another quarry 10264 

Do. of Portland stone (458) 10284 

Do. of Yorkshire paving stone (463) 

with the strata 12856 

Do. of same, against the strata 12856 

Do. of white statuary marble 13632 

Do. of granite from Cornwall, Eng-. 

land, (462) 14302 

Do. of variegated red marble, De- 

vonshire, (462) 16712 

Do. of compact limestone (467) 17354 

Do. of compact black marble 20742 

Do. of compact Italian veined marble 21783 

Do. of blue Aberdeen granite, such 

as is used for paving streets 
in London, (444) 24556 

691. It might be supposed that density, as expressed by specific 
gravity, would influence the duration of stones, or rather their re- 
sistance to fracture; but this does not appear to be the case on 
trial, for statuary marble has a specific gravity of about 2.760, 
while Aberdeen granite has only 2.625; and yet the granite oifers 
a resistance considerably greater than the marble. Neither is 
hardness a characteristic of strength, for all the marbles may be 
scratched by a knife, and will divide by the saw, and yet many 
of them approach very nearly in their power of resistance to the 
Aberdeen granite, which is very refractory. 

692. The results of the above mentioned late experiments, 
vary materially from those that had been formerly tried. Thus 
M. Gauthey, a French Engineer, tried many experiments upon 
freestones of uniform texture, selecting the hardest and softest that 
were generally used for building, and the following are a few of 
his results.* 

Hard Stone. 

8 by 8 lines crushed with 736 oz. which is equiv, to 11.5 oz. on each square line. 
8 by 12 „ 2625 „ 27.3 „ 

8 by 16 „ 4496 ., 35.1 „ 

* From Vol. IV. of Rozier's Journal de Physique: the dimensions are French 
lines or twelfths of the French inch, and consequently larger than American 
measure. 



388 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

t 

Soft Stone. 

9 by 16 lines crushed with 560 oz. which is equiv. to 3.9 oz. on each square line. 

9 by 18 „ 848 „ 5.3 „ 

18 by 18 „ -2928 „ 9. 

18 by 24 „ 5296 ',, 12.2 

Little can be deduced from these experiments, because they 
are devoid of ratio; and there is even a want of accordance in the 
results; but they show one important fact that will presently be 
noticed, viz: that the strength increases much faster than the area 
of the section, for in the first experiment each square line of sur- 
face could only support 11.5 oz.; in the second, where the area is 
not doubled, each hne could support 27.3 oz.; and in the third 
experiment, where the section is just double that of the first, each 
line could bear 35.1 oz. before it crushed. 

693. The modern experiments on timber are considerably below 
those of former writers. Thus Rondelet states* that from 5000 to 
6000 Ihs. avoirdupois is necessary to crush a cubic inch of oak; and 
from 6000 to 7000 lbs. to produce the same effect on a cubic inch 
of fir (or pine), and that the former piece was compressed to Jd 
and the latter to -J its former dimensions in the experiments. The 
later experiments having been tried with great care and pre- 
cision are, however, most to be depended upon. 

694. The late Mr. Thomas Tredgold, who is considered as one of 
high authority among modern Engineers, has also made many ex- 
periments on this subject, and he statesf that the power of cast 
iron to resist compression, was formerly much overrated. Mr. 
Wilson estimated the power necessary to crush a cubic inch of 
cast iron, at 1000 tons, or 2,240,000 lbs.\ and in describing an expe- 
riment by Mr. W. Reynolds of the Ketly Iron Works in Shrop- 
shire, it is stated that a quarter inch cube of the toughest cast 
iron, such as cannon is made from, required 448000 Ihs. to crush 
it,J but this is incorrectly stated, since the experiments were made 
for Mr. Telford, and his report upon them is, that quarter inch 
cubes of grey soft metal yielded to 80 cwt., and of gun metal to 
200 cwt. The first being equivalent to 143360 lbs., and the second 
to 350,400 lbs. on the square inch. 

695. Mr. Tredgold in a paper inserted in the Philosophical 
Magazine, (Vol. XLVIL, p. 22, for January, 1817,) asserts that 
the force necessary to crush a solid cylinder of any homogeneous 
material, should be expressed by 

Sfp r' 

* L'art de Batir par Rondclet Tom IV. p. 67. 

t Practical Essay on the strength of cast iron and other metals, by Thomas 
Tred£:old, London, 1824. 
t Nicholson's Journal, Vol. XXXV., for 1813. p. 4. 



OF RESISTANCE TO PRESSURE. 



389 



in which/ is the direct cohesive force of a square inch of the ma- 
terial obtained by experinnent, r the radius, andp=3.14159, &c., 
and from this formula he deduces that cylinders one inch in diame- 
ter of cast iron, should crush with 314160 lbs., because the direct 
cohesion of that metal was 5000 lbs. to the square inch. 

An inch cylinder of lead has direct cohesion of 3000 lbs., and 

would therefore crush with lbs. 18S49 

Fine marble, cohesion of 1000 lbs. should crush with 6283 

Fine sandy freestone 205 „ 1288 

Good brick 280 „ 1759 

but he observes, these deductions have not been compared with 

actual experiment, 

696. In a table of data appended to his excellent treatise 
on cast iron, he gives the following calculated results of what a 
square inch of each of the following substances should sustain 
without permanent alteration or fraction; and these m.aterials are 
alphabetically arranged. 

Iron, malleable lbs. 17800 

Larch 2065 

Lead 1500 

Mahogany (Honduras) 3800 

Marble (white) failed with 6060 
Oak (good English) 3960 

Pine (yellow American) 3900 
Porphyry, red, failed 35568 

Stone (Portland) do. 3729 

Tin, cast 2880 

Zinc, cast 5700 

697. Being thus in possession of the powers of different sub- 
stances to resist pressure from above, it would seem that the En- 
gineer has nothing more to do than to compute the weight of what 
has to be supported, by the table of specific gravities at the end 
of the present chapter, or other convenient means, and then to 
form a base of such material as he may select, the magnitude of 
which may be determined by the last of the foregoing tables; be- 
cause if a superficial inch of white marble, for example, can sustain 
6060 lbs., it may be inferred that a superficial foot composed of 
144 inches, laid contiguous to each other, would support 144 times 
as much, or 872640 lbs. If, therefore, we had a building, or the 
arch of a bridge to support, and it should be found by calculation 
that its materials weighed 2617920 lbs., that same weight might be 
divided by 6060, the resistive power of an inch, or by 872640, the 
resistance of a superficial foot, when the quotient would give the 
number of square inches or square ie.Gt of marble that must be used 
to support this load. In the example just given, three piers of 



Ash wood 


lbs. 3540 


Beech wood 




2360 


Brass, cast 




6700 


Brick failed with 




562 


Cast iron do. 




93000 


Chalk do. 




500 


Elm wood 




3240 


Fir, (yellow pine,) 




4290 


Do. white 




3630 


Granite, Aberdeen 


do. 


10910 


Gun metal (8 cop. 1 


tin) 


10000 



390 ON THE ABSOLUTE STRENGTH OP MATERIALS. 

one foot square each, would be required to carry the load, because 
each square foot would carry 872640 lbs., which number, multi- 
plied by three, would amount to the same as the weight of the 
load. 

698. It is found however, in practice, that the power to resist 
compression increases more rapidly than the surfaces, as before 
mentioned, and proved by the experiments of M. Gauthey (692), 
where we find that while a piece of stone of 8 lines long, by 8 lines 
broad, and consequently exposing a surface of 64 square lines, 
could only withstand a pressure of ll.Soz. upon each square line, 
that by increasing the surface to 8 by 12, or 96 square lines, each 
line could bear 27.3 oz., and when increased to 8 by 16, or 128 
square lines, each line could bear nearly 35.1 oz. before it broke, 
being three times the pressure that the same quantity of matter 
could withstand in the first experiment. 

699. To account for this change, we must look to the conforma- 
tion of solid substances. Solid matter is stated bv all writers on 
the subject, to be composed of minute particles of matter held to- 
gether by the attraction of cohesion, and those ultimate particles 
are believed to be possessed of the power of impenetrability, or 
to be infinitely hard. If, therefore, we conceive a mass of matter 
to be composed of a series of perpendicular columns of such par- 
ticles placed directly over each other in lines that are in contact 
laterally, it would be impossible that a body so constituted, could 
give way to any force, acting in the direction of such lines, how- 
ever great it might be; because as the particles are themselves 
impenetrable, they cannot sink into each other, and as the lines 
are close and parallel, they cannot for the same reason slide late- 
rally out of their places. It is, however, impossible to find any 
natural body thus regularly constituted. All things have certain 
formations that are crystalline, or composed of grains of some form 
or another, and these fit into the interstices formed by the adjoin- 
ing grains, as may be seen by inspecting a piece of sandstone with 
a magnifying glass. Such an aggregation of particles may, there- 
fore, be compared to a parcel of small shot, and if its upper sur- 
face is not level and flat, and a weight with a level bottom is 
placed upon them, those shot that are the highest, or most protu- 
berant, will be pressed down, and can only descend by pushing 
the shot under them in lateral directions, and sinking in between 
them. But let us further suppose that the shot are confined by 
an iron hoop, or the sides of a vessel capable of resisting this late- 
ral spreading; then the lower shots will be unable to give way to 
the same extent, to make room for those that are above them, and 
the shot, now prevented from sliding away, will press against each 
other; consequently, the upper stratum will be enabled to support 



OF RESISTANCE TO PRESSURE. 391 

a much greater weight than before without disturbance (which 
may be called breaking) of the mass below. 

700. This is a case very similar to what takes place in experi- 
menting upon small or large masses of matter to produce their 
fracture by compression. This fracture can only take place when 
the power applied is so great as to be capable of overcoming the 
cohesion of the particles of which the mass is composed. They 
then give way and spread laterally, which is called crushing; and 
when a cube of any material of a quarter of an inch square is 
subjected to pressure, having no external support to assist it, it 
will evidently give way much more readily than if it was sur- 
rounded by eight other cubes of the same material placed in 
close contact with it, and in one piece with itself, all being held 
together by the same power of cohesion, and forming a square 
surface of three quarters of an inch, instead of one quarter. Thus 
let a, Fig. 135, Plate V., represent the solitary cube to be expe- 
rimented upon, which would readily yield to lateral expansion, 
while it had nothing to support it: but when it is surrounded by 
the eight similar cubes h cd efg h and i, it is evident that it can- 
not spread laterally without displacing e c f and h, consequently, 
the force necessary to overcome them, must be added to that 
exerted on a; and as they are supposed to be of the same material, 
each of them would require a force equal to that which was 
before exerted upon a alone, and this would be the case if four 
cubes only, e cfh, were placed round a. But e cfh cannot give 
way without at the same time disturbing h d g and i; therefore 
the power of resistance is still further augmented. If again we 
imagine the nine cubes just spoken of, to be again surrounded by 
sixteen others, as shewn in the figure, then the resistance to com- 
pression will be much increased, for now a cannot give way with- 
out displacing two cubes on each of its sides, while those two cubes 
are held in their places by four others, two being contiguous to 
each of their sides; hence it will appear that the power to resist 
fracture by compression, should be enormously increased by ex- 
tent of surface, but what that increase may be, as regards practi- 
cal applications, has never been satisfactorily proved. What it 
should be on mathematical principles has been determined; but 
this gives a result far greater than is found to hold good in prac- 
tice, owing to the impossibility of subjecting every particle, or 
even every small space to an equal degree of pressure; and it is 
likewise a very difficult and intricate problem, because the cen- 
tral particle is supported on every side, and has the greatest 
strength, while the exterior rows have no support on one side, and 
the angular particles are deficient in support on two sides. The 
strength must consequently be an increasing series from the ex- 



392 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

tremities to the centre. Muschenbrock, Euler, and some other 
high authorities have made the strength of columns on the fore- 
going principles to be as the biquadrates of their diameters, and 
this was received as a principle by the academicians of St. Peters- 
burgh. Others again maintain that the strength increases as the 
area of the section, and such was the opinion of that accurate 
philosopher M. Coulomb; but Professor Robison makes it twice as 
much. If, however, this force be supposed to be simply equal to 
the direct cohesion, it may be inferred that the strength of a square 
bar in resisting compression, is twice as great as its cohesive 
strength, allowing that the fracture takes place in the sur- 
face of least resistance. It seldom however happens that the 
strength with which a body resists compression is in so great a 
proportion as this, to its cohesive strength, and where the sub- 
stance is in any degree composed of fibres, they must naturally 
produce great irregularities by their bending; but experience 
denies both these assumptions, and while it shows that the first is 
enormously too large, it proves equally that the other is too low, 
though not in the same degree. After all, therefore, it must be 
confessed, that the relation between the dimensions and strength 
of pillars has not yet been established on sound mechanical prin- 
ciples, nor is it probable that general principles applying equally 
to all substances, can ever be established, since much depends upon 
the internal structure of the body, and experiment seems alone to 
offer the means of coming at the truth. 

701. The illustration that has been given with the shot, applies 
to all granular bodies, such as sandstones, and the several varie- 
ties of free stone. But if we suppose a body to be of a fibrous 
texture, having all its fibres in the direction of the pressure, and 
adhering to each other by some kind of cement, such a body would 
fail only by the bending of the fibres, by which they would break 
the cement, and become detached from each other. Something 
like this may be supposed in wooden pillars. In such cases, too, 
it would appear that the resistance must be as the number of 
equally resisting fibres, and as their mutual support jointly, and 
therefore as some function of the area of the section. The same 
thing must happen if the fibres are naturally crooked and undu- 
lating, as they occur in many woods and other substances, provid- 
ed we suppose some similarity in their form. Similarity of some 
kind must always be supposed, otherwise w^e need never aim at 
general inferences. 

702. In all cases, therefore, we can hardly refuse admitting that 
the strength in opposition to compression is proportional to a func- 
tion of the area of the section. 

103. As the whole length of a cylinder or prism, is equally 



OF RESISTANCE TO PRESSURE. 393 

pressed, it does not appear that the strength of a pillar is at all 
affected by its height, unless it looses its right lined vertical posi- 
tion by bending, when a transverse strain will be produced which 
increases with the height of the pillar. But this does not fall 
within our present subject, and will be hereafter treated upon. 

704. The rule that is generally followed by practical men for 
determining the necessary strength and dimensions of a pillar or 
vertical support, is to take such of the experiments as have been 
before detailed, as may suit the case, and to multiply the result 
given, until it reaches the sought for power, and then to take only 
one-fourth or one-fifth of that quantity to work upon. Thus if a 
single square inch of brick is capable of supporting 562 Ibs,^ two 
inches should support twice that weight, or 1124 Ibs.^ and ten 
inches should support 5620 Ibs.^ and so on; but instead of trusting 
ten inches of brick to bear the 5620 lbs,, only one-fourth or one- 
fifth of that load should be placed upon it; or if the whole load 
must be carried, the surface of brickwork should be extended to 
four or five times ten inches. This has always been deemed a 
safe rule, because it is merely making the strength to increase as 
the area, and then only using about a quarter of the strength 
given by the trial. The reason for making so large a deduction 
is two fold; first to guard against imperfect workmanship, and 
secondly against natural decay. 

705. By imperfect workmanship is meant the almost impossi- 
bility, in practice, of getting heavy beams or pieces of stone to bear 
equally upon every part of the surface that is prepared to support 
them, arising from the difficulty in moving and placing heavy 
bodies, or from the support settling or sinking to a greater dis- 
tance than was contemplated, in consequence of receiving the new 
load, or its settling unequally in different parts. Thus a pier of 
brickwork containing 180 square inches of surface, might be built 
to support a burthen of many thousand pounds, which it would be 
fully competent to bear, provided the weight was equally distri- 
buted over the whole surface. But in placing it, it might happen 
that the whole would rest upon three or four square inches, which, 
being incompetent to the load, would fail, and transfer it to another 
small part equally incompetent to bear it, and thus the whole 
might fail. 

706. Provision against natural decay hardly wants elucidation. 
A pier or column of new work, composed of good and sound mate- 
rials, might be fully equal to the support of the load placed upon 
it; but when those materials, through lapse of time, begin to decay, 
they may fail and produce serious consequences. Every construc- 
tion ought therefore to be made strong enough in the first instance, 

50 



394 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

to permit a certain extent of decay taking place, without derange- 
ment of the whole fabric. 

707. Dr. Thomas Young, who has bestowed much pains on the 
subject of the strength of materials, shows that even if the whole 
surface of the support could be brought into simultaneous action, 
it ought not to be trusted to on the principle of every particle 
throughout that surface having equal strength; because all parti- 
cles as they recede from the centre towards the circumference, 
become weaker and weaker for want of mutual support, as al- 
ready explained (700). The consequence of this external weak- 
ness is that the outside particles break off, and thus transfer the 
load more directly to those in the centre, which are the strongest. 
Dr. Young observes, that in a rectangular pillar so loaded, the 
parts slide away laterally, and if the texture of the substance is 
uniform and not tibrous, the surfaces of fracture will make nearly 
a right angle with each other, supposing the resistance arising 
from the lateral adhesion in the direction of any surface or section 
to be simply proportional to that section; but if this force, like that 
of friction, is increased by a pressure which tends to bring the 
parts into closer contact, the angle left after fracture must be 
more acute. This last is the effect that most generally occurs in 
practice; because if a load is equally disposed over the top of a 
column, that load must tend to increase the contact of all the par- 
ticles beneath it. Thus if A, Fig. 136, represents the top of a 
prismatic or cylindric column, and B a heavy stone or load placed 
upon it, the tendency to break, under the first supposition, will be 
in the lines c d, c e radiating from the centre c, and dee will be 
nearly a right angle; but if B produces a tendency to compression 
of the particles in A, then the direction of fracture will be in the 
dotted lines cf, c g, and the angley c g will be more acute than 
in the former case. 

708. With a view to diminish the tendency to compression in 
A, and thereby to render the angle of fracture more obtuse, Dr. 
Young suggests that there may be an advantage in avoiding per- 
fect contact between the top of the column and the under side of 
its load, by making the former very slightly convex, and highest 
in the centre, so that the centre, which is the strongest part, shall 
bear the whole load. This convexity may be carried to the ex- 
tent of making the top hemispherical, as in Fig. 137; because a 
circle is as strong as its circumscribing square, supposing the adhe- 
sion proportional to the surface, the relative force of all its chords 
being equal.* This is one method of preventing the external parts 

* Dr. Young's Lectures on Nat. Phil., Vol. I., pp. 145 and 767, See also a long 
demonstration of this effect in the same work, Vol. II., p. 46. 



OP RESISTANCE TO PRESSURE. 395 

from breaking and falling off. But if the whole surface is level 
and brought into action, the lateral expansion may be counter- 
acted by hooping it with iron; for a hooped shaft of wood or any 
fibrous material will support more when so hooped than without 
such assistance. May not the mouldings that surmounted the 
columns of antiquity have been originally nothing more than hoops 
or bandages placed there for strength and security, and which, as 
time and improvement advanced, became the graceful capitals as 
we now see them? 

709. Whenever a body that possesses any elasticity is subjected 
to pressure, it will be found that it begins to condense or decrease 
in dimensions before the actual fracture takes place, or before the 
cohesion of its particles is overcome; and if the load be removed 
at this instant, the organic arrangement not having been disturb- 
ed, its strength will be unimpaired. With a view to express this 
effect and others that took place in the progress of experiments, 
as well as to obtain a means of comparing the resistance of any 
one substance with another. Dr. Young introduced some new terms 
which have since been so commonly adopted by all writers, that 
an explanation of them becomes necessary in this place. 

710. He states that where a weight is suspended below a fixed 
point, the suspending substance being stretched, retains its form 
by its cohesion and rigidity, or stiffness: and when the weight is 
supported by a block or pillar below it, the block is compressed, 
and resists fracture, primarily by a repulsive force, and secondly, 
also, by its rigidity. 

711. Detrusion is produced where a transverse force is applied 
close to a fixed point, with sufficient power to move the particles 
that are opposed to its action; they being held together by cohe- 
sion assisted by their rigidity; and the force thus generated is call- 
ed repulsion. 

712. Where three or more forces are applied simultaneously to 
different parts of a substance, they produce^exz^re or bending, in 
which case some of its parts will be subjected to a compressing, and 
others to an extending force. In torsion or twisting the central par- 
ticles remain in their natural state, while those that are in opposite 
parts of the circumference are detruded or displaced in opposite 
directions. Forces applied in any of these ways may produce a 
permanent alteration or change of figure of the body, which will 
not affect its strength, and is well known to all workmen, who 
call it settling, or taking a set. Thus a brick wall settles, or be- 
comes lower than when first built, by the semi-plastic mortar giving 
way to the weight of the bricks, mortar, or other load placed above 
it. A long straight stick of timber laid across the opening of a build- 
ing, will sag or sink in the middle, giving a downward convexity 



396 ON THE ABSOLUTE STRENGTH OP MATERIALS. 

to the piece; but this only goes on until the compressing force be- 
comes exactly balanced by the resisting or repellant force, and 
^ then no further change occurs; the new form becomes a perma- 
nent one, and the thing is said to have taken its set, or has arrived 
at its full settling. The limit of all these effects is fracture, which is 
the consequence of the application of any force capable of over- 
coming the strength of the substance; and the power that all bo- 
dies possess of resisting any impulse is called their resiliance. 

713. If the rigidity of a body was infinite, and all lateral mo- 
tions of its particles were prevented, the direct cohesion alone 
would be the measure of the force required to produce extension; 
in this respect, indeed, the actual rigidity of some substances may 
be considered as infinite, wherever the extension or compression 
is moderate, and no permanent alteration of form is produced; and 
within these limits, such substances may be called perfectly elas- 
tic. If the cohesion and repulsion were infinite, and the rigidity 
limited, the only effect of force would be to produce alteration of 
form; and such bodies would be perfectly inelastic, but they would 
be harder or softer according to the degree of rigidity. 

714. It is found by experiment that the measure of the exten- 
sion and compression of uniform elastic bodies, is simply propor- 
tional to the force which occasions it; at least when the forces are 
comparatively small.* Thus, if a weight of 100 lbs. lengthened a 
rod of steel one hundredth of an inch, a weight of 200 lbs. would 
lengthen it very nearly two hundredths, and a weight of 300/65. 
three hundredths of an inch. The same weights, acting in a con- 
trary direction, would also shorten it one, two, and three hun- 
dredths respectively. The former part of this law was discovered 
by Dr. Hooke, and the effects appear to be perfectly analogous to 
those that are known to take place in all elastic fluids. 

715. According to this analogy, we may express the elasticity 
of any substance, by the weight of a certain column of the same 
substance, which Dr. Young denominated its modulus of elasticity, 
and of which the weight is such, that any addition to it would in- 
crease in the same proportion, as the weight added would shorten, 
by its pressure, a portion of the substance of equal diameter. 
Thus, if a rod of any kind, 100 inches long, were compressed one 
inch by a weight of 1000 lbs, the weight of the modulus of its elas- 
ticity would be 100,000 lbs. or more accurately 99,000, which is 
to 100,000 in the same proportion as 99 to 100. In the same man- 
ner we must suppose that the subtraction of any weight from that 
of the modulus, will also diminish it in the same ratio that the 
equivalent force would extend any portion of the substance. The 

* Young's Lectures on Nat. Phil., Vol. I. p. 136, 



OF RESISTANCE TO PRESSURE. 397 

height of the modulus is constantly the same for the same sub- 
stance, while its specific gravity remains unaltered, whatever its 
breadth and thickness may be: for atmospheric air, it is about 5 
miles higjh, and for steel is nearly 1000. This supposition is suffi- 
ciently confirmed by experiments to be considered, at least, as a 
good approximation. It follows that the weight of the modulus 
of any substance must always exceed the utmost cohesive strength 
of that substance, and that the compression produced by such a 
weight must reduce its dimensions to one half; and it is found that 
a force capable of compressing a piece of elastic gum to half its 
length, will usually extend it to many times that length, and then 
break or tear it; and also that a force capable of extending it to 
twice its length, will only compress it to two-thirds. 

716. The modulus of elasticity, therefore, admits of being ex- 
pressed in two forms, according to our wish to use it as a general 
or specific term. If it is general, then it can only be expressed in 
height; but if it is specific, then it may be expressed either in 
height or in weight, or by both conjoined. Thus in stating that 
the modulbs of elasticity for the air of the atmosphere is about 5 
miles high, we are to understand that a stratum of air, 5 miles 
thick from the surface of the earth, will press upon the air at the 
earth's surface with a certain force equal to about half the pres- 
sure of the whole atmosphere. But this pressure will be equally 
exerted according to surface, upon every square foot or square 
mile of the earth as upon its whole surface, therefore this is a 
general expression. If, on the contrary, we desire to express the 
modulus of elasticity of air upon a single square inch of the earth's 
surface, we can in like manner say it is 5 miles high: but as the 
surface is defined and limited to one inch, the dimensions of the 
pressing prism of air is likewise defined, and can be nothing but 
an inch square prism of air, 5 miles high. The dimensions being 
* given, its weight can be ascertained, and as the whole pressure 
of the atmosphere is usually rated at 15 lbs. upon each square inch, 
so the half of that pressure will be 7^ lbs.; consequently we may 
say the modulus of elasticity of air is 5 miles high, or is 7 J lbs. on 
the square inch, which will be the same thing. 

Let the same principles be applied to lead, the height of the 
modulus of elasticity of which is stated to be 146,000 feet^ w'hile 
the weight of its modulus upon the base of a square inch is 
720,000 lbs. This is saying, in other words, that a weight of 
720,000/65., either in the form of a perpendicular column, or pro- 
duced by a lever, or applied in any other way upon the side of 
an inch cube of lead, would squeeze or reduce it in thickness to 
a certain extent, to one half of its former dimensions for example: 
But a stratum of lead 146,000 (eet thick, would produce the same 



398 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

proportionate reduction upon another stratum of lead, however 
extended its surface, placed under it, provided the two surfaces 
were equal. Then in order to compare the elasticity of lead with 
that of cast iron, we must tind a height or weight that will pro- 
duce the same efFectupon cast iron that 146,000 feet or 720,000/65. 
produced upon lead. The height of the modulus of elasticity for 
cast iron is 5,750,000 feet, and for the base of an inch square, is 
18,400,000 lhs,f (as given by Tredgold,) and the quantities that 
belong to lead being compared with those that belong to cast iron 
will express the proportionate elasticities of these two substances, 
or the proportionate resistance they will offer to the action of any 
load placed upon them. 

717. The moduli of elasticity can, therefore, be put in a tabular 
form for ready use, and by which the respective advantages of 
the several materials are exposed to view at once, as in the fol- 
lowing short example, in which the numbers are extracted from 



Tredgold. 














Height of Modulus of 


Weight of Modulus for 


Modulus of 




Elasticity. 




base of 1 square inch. 


Resiliance. 


Ash wood, 


4,970,000 feet 


1,640,000 pounds 


7.6 


Beech wood, 


4,600,000 




1,345,000 


» 


4.14 


Brass cast. 


2,460,000 




8,930,000 


» 


5.0 


Cast iron. 


5,750,000 




18,400,000 


J? 


12.7 


Elm wood, 


5,680,000 




1,340,000 


>j 


7.87 


Fir or Yellow Pine, 


8,330,000 




2,016,000 


>? 


16.4 


Do. white ,, 


8,970,000 




1,830,000 


j> 


7.2 


Gun metal brass. 


2,790,000 




9,873,000 




10.4 


Iron, malleable. 


7,550,000 




24,920,000 


»> 


12.7 


Mahogany, 


6,570,000 




1,596,000 




8.0 


Marble, 


2,150,000 




2,520,000 


>) 


1.3 


Mercury, 


750,000 




4,417,000 






Oak, 


4,730,000 




1,700,000 




9.2 


Slate, 


13,240,000 




15,800,000 


>> 


8.4 


Steel, 


8,530,000 




29,000,000 






Stone, (Portland,) 


1,672,000 




1,530,000 




0.5 


Tin, (cast,) 


1,453,000 




4,608,000 




1.8 


Zinc, (cast,) 


4,480,000 




16,680,000 


j> 


2.4 



718. Mr. Tredgold observes,^ that a set of general numbers of 
comparison to exhibit the power of bodies to resist blows or im- 
pulses, and which might be termed their modulus of resiliance, 
would be extremely convenient on many occasions; and as such 
numbers may be easily obtained by a simple process that he de- 
scribes, and he has calculated many of them, the right hand 

* Essay on Strength of Cast Iron, p. 250. 



ON FORCE OF TENSION. 399 

column of the foregoing table contains such numbers as given by 
himself. 



Of the Force of Tension. 

71&. The effects of tension, or the power that substances have 
of supporting weights attached to them, must next be examined. 
This subject has been much more extensively written upon than 
that which is just concluded, and is at the same time of a more 
simple character and more easy to experiment upon. After the 
observations already made, it may, therefore, be investigated in 
few words. 

720. Tension, which is produced by a body being fastened at 
one end, while a force is applied to its opposite extremity to tear 
it from its attachment, or break it asunder, is opposed solely by 
the attraction of cohesion of the body under experiment, with very 
little modification of its action by any particular circumstances. 
If we conceive a long cylindrical or prismatic body, such as a rod 
of metal or wood, or a rope to be fastened at one end, and to hang 
down perpendicularly, while the power it has to resist is fixed to 
the other, every part of it will be equally strained or stretched if 
we conceive such a body to be without weight, but as this is an 
impossible case, all parts of such body will be equally streched by 
the load, but unequally strained by the amount of its own weight, 
which must be added to the power employed, and this last quan- 
tity will be a continually increasing series from the bottom, where 
it is nothing, to the top, where it is the full weight of the body 
operated upon. On a large scale this weight must never be ne- 
glected; but as experiments on the cohesion of bodies are usually 
tried on short pieces, the weight of which hardly bears an appre- 
ciable proportion to their strength, this element in the calculation 
may be safely overlooked, and is accordingly discarded in the ob- 
servations about to be made. 

721. Since all parts of a body thus become equally strained, it 
follows that the strains in any transverse section of such body 
must be equal to each other; consequently, if the body is perfect- 
ly homogeneous or composed of particles all alike in substance 
and arrangement, no one part of the bar can be weaker than 
another; and if the force applied is not sufficiently great to dis- 
turb the internal organization, such body will not be weakened 
by the experiment, which may be repeated an infinite number of 
times, or what is equivalent, may be continued permanently with- 
out danger of failure. But if the arrangement of particles has 



400 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

been disturbed beyond the sphere of their elasticity, the body will 
be permanently weakened, or may even break. 

722. This disturbance of organic formation may be judged of 
by the effects that take place; for most things subjected to the in- 
fluence either of compressing or extending influences, will give 
way to a certain extent, by contracting in the first instance, and 
stretching in the second. But when the power producing either 
of these actions is removed, the bodv will revert to its former, or 
very nearly former dimensions, provided its texture remains unin- 
jured. This applies more particularly to granular bodies, because 
all such as are fibrous, and particularly with crooked fibres, will 
admit of very considerable permanent elongation without effect- 
ing their strength; because it may arise from drawing the crooked 
fibres straight. This is observable in all new ropes which un- 
twist and elongate very sensibly when first used. Straight grain- 
ed woods, such as pine or fir, will not admit of much stretching 
without fracture, and they break abruptly when over strained; 
while oak and birch, which have very undulating fibres, stretch 
sensibly, and do not break suddenly, but give warning of the event 
by shewing visible derangement of texture, accompanied by a 
creeking noise, which carpenters call complaining. Notwithstand- 
ing the immense variety which nature exhibits in the structure 
and cohesion of bodies, there are certain general facts of which 
we may avail ourselves with advantage. 

723. It may be asserted as a general proposition that the 
strength of any substance under the influence of an extending 
force, is proportional to the area of the section of that substance, 
such section being taken perpendicularly to the line of the extend- 
ing force. This must be the case where the texture is perfectly 
uniform, as in glass, and the ductile metals. The same must be 
admitted with respect to bodies of a granulated texture, where 
the granulation is regular and uniform; and likewise of fibrous 
bodies, if we suppose their fibres equally strong, equally dense, 
and similarly disposed through the whole section. It follows, there- 
fore, that all cylindrical or prismatic rods are equally strong in 
every part, and will break alike in any part; and that bodies that 
have unequal sections will always break in the slenderest part; 
also that the length of the cylinder or prism, has no effect on the 
strength; and the vulgar notion that it is easier to break a very 
long rope than a short one, is a great mistake. 

724. From the above we learn, that the absolute strength of 
bodies that have similar sections, are proportional to the squares 
of their diameters or homologous sides of the section. 

725. The weight of a body itself may be employed to strain and 
break it. It is evident that a rope may be so long as to break by 



ON FORCE OP TENSION. 401 

its own weight. When the rope is hanging perpendicularly, al- 
though it is equally strong in every part, it will break towards its 
upper end, because the strain on any part, is the weight of all that 
is below it; and its relative strength, or the power it will have of 
withstanding any strain laid on it, is inversely as the quantity 
below that part. 

726. On this principle a set of comparative numbers might be 
found that would express the absolute cohesion of bodies, or the 
quantity in length and weight of the same substance that would 
produce separation, supposing the areas to be constantly the same, 
and such numbers might be called the moduli of cohesion. The 
writer is not aware that this has been done to any extent, but the 
few following results calculated by Professor Leslie, show the 
possibility and utility of such a table. The following are for 
prisms an inch square.* 

Teak 12,915 lbs, 36,049 feet long. 

Oak 11,880 32,900 

Sycamore 9,630 35,800 

Beech 12,225 38,940 ' 

Ash 14,130 42,080 

Elm 9,720 39,050 

Memel fir 9,540 40,500 

Christiana deal 12,346 55,500 

Larch 12,240 42,160 

727. When a rope is stretched horizontally as in towing a ship, 
the strain arising from its weight often bears a very sensible pro- 
portion to its whole strength. Thus let a eh. Fig. 138, Pi. V., be 
any portion of such rope, and a c,h che tangents to the curve into 
which its gravity bends it. Complete the parallelogram a dh c. 
It is well known that the curve is a catenaria, and that d c must 
be perpendicular to the horizon, and that d c is to a c, as the 
weight of the rope a c 6 is to the strain at a. 

728. In order that a suspended heavy body may be equally able 
in every part to carry its own weight, the section in that part 
must be proportional to the solid contents of all below it. Sup- 
pose it a conoidal spindle formed by the revolution of the curve 
A a e. Fig. 139, round the axis C E. We must have A C^ : a c^= 
AEB solid: a E 6 solid. This condition requires the logarithmic 
curve for A a e, of which C c is the axis. 

729. These are the chief general rules which can be safely 
deduced from our knowledge of the cohesion of bodies. To make 
any practical use of them, it is necessary to have some measures 
of the cohesion of such bodies as are commonly employed in ma- 

* Gregory's Mathematics for Practical Men, p. 407. 
51 



402 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

chines or constructions where they are exposed to this kind of 
strain, and these can only be obtained by experiments. These 
experiments must not, however, be implicitly relied on, notwith- 
standing all the care and precision with which they may have 
been made; because natural substances are liable to so great a 
variety of changes, that we can never feel perfect assurance that 
the material we possess, agrees in every respect with another of 
similar name, upon which an experiment has been tried. Timber 
produced by cold countries is slow in growth, and in general much 
harder and stronger than that of hotter climates. Metals differ 
by many circumstances that have never been accounted for, as 
well as from their purity; thus their strength is affected not only 
by the fuel, but the heat with which they have been melted, the 
moulds into which they have been cast, and the treatment they 
afterwards receive, such as forging or hammering, wire-drawing, 
tempering, annealing, and the like. 

730. It might be supposed, that giving repeated blows of a ham- 
mer to a piece of metal, or drawing a fine rod of it through holes 
in a plate of hard steel, so as to diminish its diameter and increase 
its length to a vast extent, would affect the internal corpuscular 
arrangement of the metal, and thus injure, if not destroy its cohe- 
sion. The first of these processes takes place in forging a piece 
of metal, and the latter in wire-drawing, or converting it into wire; 
and yet experience shows that both these processes increase the 
cohesive power very considerably. Thus gold, silver, and brass, 
have their cohesive strength tripled, and copper and iron have it 
more than doubled; and the hardness and density of the metal are 
at the same time increased. So that after drawing the metal 
through a few holes, it becomes necessary to heat it red hot, and 
suffer it to cool slowly, which restores its softness and ductility. 
This heating and cooling is called nealing or annealing, and it pre- 
vents the metal from cracking. 

731. For the reasons above stated, the student must not con- 
sider the following tabulated results of experiments that have been 
tried as fixed data, but must look upon them rather in the light of 
general values deduced from the average of many trials. Before 
he can rely upon the numbers given, he must assure himself that 
he possesses the same material; that is to say one of equal good- 
ness and strength, and this he can only do by experiment. And 
fortunately such experiments are cheap and easy, in comparison 
with those made on the compression of materials; nothing more 
being necessary than to fix the strips of wood to be tried, firmly 
at their upper ends, and to apply a long wooden lever with a shift- 
ing weight like a steelyard to the lower extremity, the connection 
between the lever and strip of wood being made by a small 



ON FORCE OF TENSION. 



403 



smith's vice attached to the upper side of the lever. If metal has 
to be tried, the rod of metal may be formed with a hole or eye at 
each end, and then a strong hook fixed in a beam of wood above, 
and another hook attached to the lever as in Fig. 140, will be all 
the apparatus necessary for this purpose. The strips of wood 
should not exceed J inch square, and the pieces of metal ^ inch. 
By such means he will readily determine whether the metal or 
other materials he possesses, is inferior or superior in strength to 
the examples given in the tables, and will thus be able to work 
with confidence. 

732. Brick and stone are from their brittle nature never thrown 
into a state of tension, or employed for supporting pendant loads; 
therefore their properties in this respect have not been estimated 
or examined; but the materials usually resorted to for this purpose, 
are bars of metal and chains, cylindrical or prismatic pieces of 
timber, ropes, and leather or raw hide; and the following tables 
show the power of those substances most commonly met with and 
used, to support loads, the measure of their cohesion being the 
number of pounds avoirdupois, which are just sufficient to tear 
asunder a rod or bundle of one inch square. From this it will be 
easy to compute the strength corresponding to any other dimen- 
sions. 



Metals, 

Grold, cast, varies between 

Silver, cast do. 

f Japan 
I Barbary 
Copper, cast -( Hungary 
I Anglesea 
l^ Sweden 

Cast Iron varies between 

C ordinary 
Bar Iron ) good 

f best Swedish and Russian 

Steelbar?^^^^ . , 

( tempered straw colour 

r Malacca 
Banca 
Tin, cast-| block 

I English block 

(^ Do. grain 
Lead cast 

Regulus of Antimony 
Zinc 
Bismuth 



lbs. 

5 20,000 

I 24,000 

J 40,000 

\ 43,000 

19,500 

22,000 

31,000 

34,000 

37,000 

5 42,000 

\ 59,000 

68,000 

75,000 

84,000 

120,000 

150,000 

3,100 

3,600 

3,800 ) 

5,200 5 

6,500 

860 

1,000 

2,600 

2,900 



Results obtained by Mr. 
George Rennie as given by 
Dr. Gregory, Math, for Pract. 
Men, p. 408. 

- 19,072 

- , - 19,096 

- 55,872 

- 72,064 
Cast Steel 134,256 



4,736 

1,824 



The above table is extracted from Professor Robison's Mechani- 
cal Philosophy, Vol. L, p. 398, and no authority for the experi- 
ments is quoted. The results vary considerably from those stated 



404 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

to have been deduced from Mr. Rennie's experiments, as given by 
Dr. Gregory, and his numbers as far as they go, are, therefore, 
placed on the right hand side of Dr. Robison's, that the difference 
may be apparent at the first glance. Unfortunately for the cause 
of certainty on this subject, neither of these sets of numbers ap- 
pear to accord with those of Mr. Rennie, as given in his paper 
before referred to, for which reason the following extract from 
Mr. Rennie's paper is given. 

733. The experiments were tried with the same iron lever ap- 
paratus that has before been referred to (688); and Mr. Rennie 
observes, "that the lever was used as in the former case, but the 
metals were held by nippers made of wrought iron, with their ends 
adapted to receive the bars, which, by being tapered at both ex- 
tremities, and increasing in diameter from the actual section, and 
the jaws of the nippers being confined by a hoop, confined both. 
The bars which were 6 inches long, and ^ inch square, were thus 
fairly and firmly grasped." The following are a few of the expe- 
riments that were tried 30th of April, 1817. 

J inch bar of Cast Iron, cast horizontally, broke with 1166 lbs. av. 
Cast Iron, cast vertically „ 1218 

Cast Steel, previously tilted „ 8391 

Blister Steel reduced by the hammer 8322 

„ -Shear Steel do. do. 7977 

„ Swedish Iron do. do. 4504 

English Iron do. do. 3492 , 

Hard Gun Metal (mean of 2 trials) 2273 
Wrought Copper, reduced by hammer 2112 
Cast Copper „ 1192 

„ Fine Yellow Brass „ 1123 

Cast Tin „ 296 

„ Cast Lead „ 114 

734. As all these experiments were made on J inch square bars, 
sixteen of which laid in close contact with each other, would con- 
stitute a square inch, it may be inferred that multiplying any of 
the numbers above given, would produce the amount of strain that 
would break a bar an inch square; but it is found in practice, that 
a number of small bars thus laid together, will bear a greater pro- 
portion of load than a single bar equal to the sum of all their 
areas. This anomaly is believed to proceed from the greater per- 
fection with which small bars may be wrought and prepared than 
large ones, as all metals are improved in their strength by ham- 
mering or wire-drawing; so the effect of hammering sixteen small 
bars separately, will add more to their strength, than hammering 
on a large bar equal to the sum of their areas. Metals can only 
be improved in their strength by hammering or wire-drawing, in 



J? 

>5 



ii 

99 



ON FORCE OF TENSION. 405 

consequence of these operations forcing their constituent particles 
into a closer state of aggregation; and this can easily be done in 
small bars, because from their want of reaction, they yield to 
every blow of the hammer, and its effect is transmitted through 
their whole substance; while the reaction of a large and heavy 
bar opposes this effect, and the condensation is more confined to 
the surface. A number of small bars acting simultaneously, are, 
therefore, found to produce more strength than one large bar equal 
in size to their sum. It likewise explains why a faggotted bar 
(588) of iron should be stronger than one that has not undergone 
the operation. 

735. This property of small bars induced Mr. Telford to pro- 
pose supporting the justly celebrated and stupendous iron suspen- 
sion bridge of Menia in Wales, by iron wires instead of bars of 
iron; and this would in all probability have been carried into effect, 
had it not been for the practical difficulty of preventing oxidation 
of the wires. The thousands of wires that must have been used 
for this purpose, would of course have exposed an enormous sur- 
face to the action of the air, compared with the surface of the 
same area of iron in solid bars. It was proposed to twist the wires 
together like ropes, and to protect them on the outside with paint- 
ed canvass, while all the internal cavities were filled with paint, 
tar, or some substance that should protect the iron. Still as the 
wire ropes could not be expected to be stationary, but would be 
constantly subject to the action of wind, and the vibrations produc- 
ed by the traffic passing over the bridge, it was feared that this 
might break away the cementing material, and leave interstices 
that would catch and retain water by capillary attraction, and 
that the wires in the insides of the ropes, rendered invisible by 
those that encompassed them, might rust away unperceived and 
endanger the whole fabric. A scheme, therefore, that was per- 
fectly good in theory, was of necessity given up from the practi- 
cal difficulties that attended its execution, and iron bars were 
used as the suspending rods, in place of the wire ropes as first pro- 
posed. 

736. The experiments of Mr. George Rennie are more to be 
confided in than perhaps any that preceded them, for they were 
performed under peculiar circumstances, which give them value. 
They were not like some others, prompted by the desire of grati- 
fying scientific curiosity, but were intended to establish actually 
useful results. Mr. John Rennie, the justly celebrated Engineer 
of England, was employed to construct the Southwark Bridge 
over the river Thames in London, which was proposed to be made 
of only three cast iron arches; the central one to have a span or 
opening of 240 feet, and the two side arches of 220 feet each. 



406 ON THE ABSOLUTE STRENGTH OP MATERIALS. 

The central arch was therefore larger than any arch that had 
been constructed in the world, and the undertaking was so stu- 
pendous that it excited great public interest, as well as doubts in 
the minds of scientific men, as to its practicability. It was feared 
that the expansion and contraction of so large a mass of iron, from 
changes of temperature, would endanger it; and moreover, that the 
weight of the materials would be so enormous, that its own parts 
would crush each other, or destroy the stone piers upon which it 
was to stand. Before hazarding so great an undertaking, it there- 
fore became necessary to call every aid of mathematics and ex- 
periment into play. The venerable Dr. Hutton, whohad devoted 
great attention to the mathematical principles of arches, was, 
among others, constantly consulted, and experiments on the com- 
pression and extensibility of iron and stone being necessary, they 
were tried by Mr. Rennie, and those who assisted him with their 
advice and investigations, in the most perfect and careful manner, 
with apparatus made for the express purpose, without limitation 
as to expense, and may, therefore, be considered as more rigidly 
accurate than any others that preceded them. They are no 
doubt the investigations of the elder Rennie, and his able assist- 
ants; although Mr. Rennie thought proper to give the credit of 
them to his eldest son, Mr. George Rennie, who was professionally 
associated with his father, and probably might have been the sole 
conductor of the experiments. These circumstances are, however, 
only mentioned to show the means that Mr. George Rennie pos- 
sessed for experimenting, and the reliance that therefore may be 
placed in whatever he asserts in his valuable communication to 
the Royal Society before referred to. 

737. Mr. Muschenbrock made many experiments on the tena- 
city of the metals in which much confidence has always been 
placed; and he states the remarkable fact, that almost all the 
mixtures of metals are more tenacious than the metals themselves. 
This change of tenacity depends on the proportions of the ingre- 
dients; and the proportion thatproducesthe most tenacious mixture, 
is different in different metals. The following results are se- 
lected from his experiments, the proportions here given being those 
which produce the greatest strength. 

Two parts of gold with one of silver lbs, 28,000 

Five parts of gold with one of copper 50,000 

Five parts of silver with one of copper 48,500 

Four parts of silver with one of tin 41,000 

Six parts of copper with one of tin 41,000 

Five parts of Japan copper with one of Banca tin 57,000 

Six parts of Chili copper with one of Malacca tin 60,000 

Six parts of Swedish copper with one of Malacca tin 64,000 



ON FORCE OF TENSION. 407 

Brass, consisting of copper and zinc in unknown quantity 51,000 
Three parts of block tin with one of lead 10,200 

Eight parts of block tin with one of zinc 10,000 

Four parts Malacca tin with oneofregulus of antimony 12,000 
Eight parts of lead with one of zinc 4,500 

Four parts of tin with one of lead and one of zinc 13,000 

738. These numbers are of considerable use in the arts. By 
them it will appear that mixtures of copper and tin produce alloys 
of great strength, and accordingly this compound is called gun 
metal, from its being constantly resorted to in the formation of 
brass ordnance. The greatest strength of copper alone never 
exceeds 37,000, and tin alone 6000; yet by mixing these two me- 
tals, the tenacity of the compound is almost doubled, at the same 
time that it is harder, and yet more easily wrought. It is, how- 
ever, more fusible, which is a great inconvenience. A very small 
addition of zinc almost doubles the tenacity of tin, and increases 
the tenacity of lead five times; and a small addition of lead doubles 
the tenacity of tin. The last are mixtures of the cheaper 
metals, and a knowledge of these changes will enable Engineers 
to augment the strength of steam or water pipes, and to produce 
pipes of such metal and of such thickness and strength as shall be in 
proportion to the pressure to which they may be exposed. 

Of Woods. 

739. In addition to what has been already stated about timber 
in the section allotted to that subject (532), it may be remarked, 
that a certain age is necessary to the full vigour and strength of 
timber, which age cannot be defined, since it depends not only 
upon the species, but upon the soil and climate in which the tree 
grows. Maturity of growth appears to be essential to the good- 
ness of timber, for a young tree or sapling never possesses the 
strength or durability of a full grown tree; and if it is over aged, 
decay always begins in the heart or centre. When timber is in 
its proper state of maturity, the heart or centre is always prefer- 
red; but among the experimenters who are most relied upon, a 
difference of opinion exists as to the value of the heart. Thus, 
Muschenbrock's experiments tend to prove that the heart is the 
weakest part of the tree, while Buffon asserts a directly contrary 
result, but without experiments in proof of it. This discrepancy 
can only be accounted for by supposing that these able experi- 
menters used wood of very different ages. In young shoots, as well 
as in young trees, the central pith is always large, light and porous, 
and the rings of wood that surround it partake of its properties. 
But when the tree or branch has arrived at full maturity, the pith 



408 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

almost disappears, and the surrounding wood becomes the hardest 
and most sound. Whether the small tube of pith that remains, 
may be the means of collecting and retaining water and humidity 
that may not be drawn off by the healthy secretions of the tree, 
we will not pretend to say; but certain it is, that in old age the 
decay of a tree begins at the pith, and proceeds gradually out- 
wards to a certain extent, and thus it is that we find old trees 
hollow, and that many sticks of timber, apparently sound on their 
external surfaces, will contain bad or decayed parts in their inte- 
rior, which cannot be discovered till the stick is opened by saw- 
ing. (567.) 

740. The wood next the bark called the white or bleuj is weaker 
than the rest, and it gradually increases in strength as we re- 
cede from the centre to the blea. In respect to altitude, the 
wood is stronger in the middle of the trunk than at the springing 
of the branches, or at the root; and the wood of the branches is 
weaker than that of the trunk. All branches proceed from near 
the centre of the tree, or at any rate from that ring from which 
they have sprouted. The springing of every branch, therefore, 
produces what is called a knot, and knots weaken timber consid- 
erably, by the contortion of the fibres which they produce; and 
hence the advantage of selecting clean timber, i. e. timber free 
from knots, for good and strong work. When trees grow close 
together, as in forests, the absence of light, and free circulation of 
air, is unfavourable to the production of branches; hence, as before 
noticed, (542,) forest trees are less subject to knots, and generally 
produce longer and straighter timber, than trees that grow singly; 
and the white wood or blea may be in a great measure got rid 
of by barking the tree some months before it is cut down. (534.) 
Still the wood of single trees is generally harder and more com- 
pact than that of such as have not had the full advantage of sun 
and air. Those woods in which the annual rings are closest to- 
gether, are the most hard and durable; and notwithstanding sea- 
soning greatly improves all timber for general use, still all woods 
are more tenacious and capable of bending in the green than in 
the dry state. 

741. The only author who has put it in our power to judge of 
the propriety of his experiments on wood, is Muschenbrock. He 
has described his method of trial minutely, and it seems unexcep- 
tionable. The woods were all formed into slips fit for his appa- 
ratus, and part of the slip was cut away to a parallelopiped of -^th 
of an inch square, and therefore 2h^h of a square inch in section. 
From this the absolute strength of square inches were deduced, 
and were as follows: the numbers being the average of a great 
number of trials on each species. 



ON FORCE OF TENSION. 409 

Locust tree lbs. 20,100lElder lbs, 10,000 



Beech and Oak 17,300 

Alder 13,900 

Elm 13,200 

Willow 12,500 

Ash 12,000 



Fir 8,330 

Walnut 8,130 

Pitch pine 7,650 

Cyprus 6,000 

Poplar 5,500 



Plum 11,000 Cedar 4,880 

The nunnbers set against elm and ash are the result of more 
than fifty experiments tried upon slips taken from different parts 
of the tree, and all the experiments were tried with so much care 
that there can be no reason for want of confidence in the results. 
Still they are considerably higher than those given by some other 
writers. Thus M. Pitot on the authority of his own experiments 
and those of M. Parent, says that 8640 lbs. is the utmost strength 
of a square inch of sound oak, being very nearly half what the 
above table states. Still, however, the numbers in the table are 
the utmost strains the slips could bear, or such as produced sepa- 
ration, and no one employing timber would think of loading it to 
any thing like this extent. It may be said in general, that two- 
thirds of the weights given would sensibly impair the strength after 
a considerable time, and that one-half is the utmost that can re- 
main suspended by them without risk forever; and it is this last 
allotment, or even less than it, that the Engineer should reckon 
upon in his constructions. 

742. According to Mr. Emerson, the load which may be safely 
suspended to an inch square, is as follows: 

Iron ' lbs. 76,400 

Brass 35,600 

Hempen rope 19,600 

Ivory 15,700 

Oak, Box, Yew and Plum tree 7,850 
Elm, Ash, Birch 6,070 

He gives as a practical rule, that a cylinder whose diameter is 
d inches, loaded to one-fourth of its absolute weight, will carry as 
follows. 

Iron 135] 

Good rope 22 K-, , 

Oak 14 f^^^- 

Fir oj 

743. The rank which the different woods hold in Mr. Emerson's 
list, is very different from that in Muschenbrock's. But it is dif- 
ficult to obtain precision in experiments of this kind, especially 
when so few have been tried and recorded. Such experiments 
seldom carry sufficient interest to induce individuals to attempt 
them, and the proper apparatus for repeating them is too heavy 
and costly to be within the reach of most people. Such matters 

52 



Walnut, Plum 




lbs. 5,360 


Red Fir, Holly, Cedar, 


Plane 


5,000 


Cherry, Hazle 




4,760 


Alder, Beech, Willow 




4,290 


Lead 




430 


Freestone 




914 



410 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

ought, therefore, to be taken up and prosecuted at the navy yards, 
or other public establishments of different nations; because there 
a knowledge of the strength of materials is of first rate import- 
ance, and until such public experiments are established and pub- 
lished, it is in vain to hope for certain and precise results, which 
can only be extracted from the compared results of numberless 
experiments conducted and recorded with the utmost care and 
precision. 

744. Bars of metal or wood, such as have been referred to, 
should always be used when bodies are required to be steadily and 
durably supported; but when flexibility is necessary, as in raising 
loads, by drawing the suspending medium over a pulley, or wind- 
ing it round a capstan or cylinder, chains of metal, or ropes and 
straps must be resorted to; and what has already been said upon 
rods of metal, will of course apply to chains composed of such 
metal. The action is nevertheless not precisely the same as when 
a direct force draws upon a rod of metal, but is of a more com- 
plicated nature, partaking of an extending and lateral or detru- 
sive force thrown into action at the same time. The strength of 
metal chains was not much attended to until an attempt was made 
about 30 years ago, to introduce them into sea service for cables, 
in lieu of the hempen ones that had been previously used. At 
first they met with most decided opposition, and many objections 
were urged against them, among the principal of which was the 
brittle nature of iron, making it liable to break suddenly when 
subjected to a great strain; the trifling elasticity iron possessed, 
and the great weight of the material. It was urged that a hemp 
cable would expand considerably when tightly stretched, and thus 
was in less danger of breaking from sudden jerks or concussions. 
Experience has, however, gradually cleared away every objec- 
tion, and few vessels are now without their iron cables. If their 
weight is superior to a hemp cable of equal strength, their bulk is 
incomparably less; and from their flexibility, they are much more 
easily managed, coiled away, and occupy little room. Their 
weight, formerly complained of, is now deemed one of their great- 
est advantages; for when a ship is riding at anchor, the chain cable 
from its weight, partly sinks to the bottom, and partly forms a 
curve leading to the vessel; so that if the vessel is urged by wind 
or current away from her anchor, the chain is taken up and be- 
comes nearly straight, and by its constant tendency to sink again, 
is found to give much more play to the vessel than a rope cable 
could do; for a hemp cable, from its buoyancy, would become nearly 
straight, with very Httle tendency to sink, and consequently could 
give no play beyond the mere expansive power of its materials. 
If the chain cable is not wanted, it may be stowed in the hold, or 



ON FORCE OF TENSION. 411 

be used as shifting ballast, while a hemp cable would soon rot, if 
not exposed to air. Captain Samuel Brown of the British Navy, 
was a staunch advocate for the introduction of iron cables, and 
became an extensive manufacturer of them; and being a man of 
skill and science, tried many experiments upon their strength to 
prove their competency, when among other points that thus be- 
came settled, it was proved that a chain cable formed of l^ inch 
iron, was superior in strength to the largest hemp cable that is 
made, which is nearly 8 inches in diameter, or 24 inches in cir- 
cumference. 

745. Chain cables are made out of round or bolt iron, which has 
been stated to be the least trustworthy of any bar iron (581), but 
when this kind of iron got into demand for cable making, it be- 
came necessary to hammer it, and pay more attention to its fa- 
brication, in consequence of which the best iron is selected and 
manufactured with great care, when it is sold under the name of 
cable iron, and when this can be procured, it is the best and most 
tenacious iron that is made, having nearly double the strength of 
common bars. 

746. If the links or rings of a chain are made circular, the force 
of tension exerted upon it, will draw or extend them into the oval 
form; consequently, this shape should be given to all links in the 
first instance. It might then be supposed that if the force was suf- 
ficiently great, it would draw out or extend the links into longer and 
narrower ovals. But the experience of Captain Brown proved 
that instead of this effect taking place, the compound force exerted 
on each link, caused its two sides to collapse before it began to 
expand, thus making each link to assume nearly the form of the 
figure 00, by which the links passing through each other become 
so tightly and mutually embraced as to destroy the flexibility of 
the chain. To obviate this inconvenience, Captain Brown intro- 
duced a small column or stretching piece of cast iron into each 
link to maintain the two sides at their proper distance, and this 
proved so effectual, and added so materially to the strength of the 
chain, that he obtained a patent for the contrivance, and it is now 
generally used. Every chain is proved as to its strength before 
it leaves his manufactory, and the result of some of his experi- 
ments on the strength of iron chains, will be found in a place 
where probably they would not be searched for, viz: in Barlow's 
Essay on Strength of Timber, pp. 221-237. 

747. Small iron chains are now very generally used instead of 
ropes in cranes for raising iron and stone for building purposes, 
and in stone quarries and coal mines; and the account of their 
performance at the Old Park Iron Works in Shropshire, England, 
as given by the proprietor, Mr. G. Gilpin, and published in the 



412 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

Transactions of the Society for the Encouragement of Arts, Manu- 
factures and Commerce of London, confirms their decided advan- 
tage. He says, "after three years experience of the use of a 
chain, without any accident or impediment, I have ascertained 
that its cost compared with a rope, is more than as 43 to 171. 
That is to say, the new chain cost ^643, and at the end of three 
years' use, was not a quarter worn out; while formerly ten ropes 
at 8 pence a pound, were completely worn out in the same period, 
and after deducting the value of the old ropes the cost was dB171." 
When Mr. Gilpin first thought of adopting a chain, he was fear- 
ful that its weight (being 110 yards long) Would impose a diffi- 
culty, by increasing the load to be drawn up the shaft of the mine; 
but he found a chain of 5 lbs. to the yard, or weighing 550 lbs., 
was amply strong enough for his purpose; and as the rope was 
necessarily large, to be equally strong with the chain, the two 
weighed very nearly alike. 

748. In computing the strength of iron chains, it will only be 
safe to consider them the same as a single rod of wrought iron, 
equal in size to that the links are made from. It is true each 
link has two sides, which would give the appearance of double 
strength; but the iron is only single at the place where any one 
link bears upon another. This bearing is not one that is direct, 
but partakes of the nature of a lateral force at the point of con- 
tact, and an extending one upon the two sides of the link; and the 
writer is not aware that this complex action has ever been con- 
sidered and investigated mathematically, nor is he aware of the 
existence of a table giving the strain that small chains will bear 
without fracture. The weight of short linked chain fit for cranes 
or working over puUies, made of the best iron, from the experi- 
ments of a friend, has already been stated (656). 

749. Ropes consist of many small fibres united together by 
twisting or spinning, which answers a double purpose. It unites 
the fibres together, thus causing them all to act at the same time, 
and it thereby increases the general strength; for if one fibre is 
weaker than another, or weaker in one part of its length than in 
another, it derives strength and support from the other fibres that 
are contiguous to it, 

750. On examining the diflferent fibrous materials in common 
use according to their diameters, silk is decidedly the strongest, 
and flax, hemp, cotton, and other vegetable matters follow in suc- 
cession. Silk and flax are too expensive to be used on a large 
scale, and cotton is too weak; therefore hemp is the material 
generally resorted to in Europe for making ropes; but diflferent 
countries adopt such materials as are most convenient to themselves. 
Accordingly all the ropes that are used in South America and 



ON FORCE OP TENSION. 413 

Mexico are made from the fibres of the aloe. (The agave of the 
country, and disticha of Linnaeus.) The rigging and ropes of the 
native East India shipping are made from the fibrous external coat 
of the coca nut. A great deal of the rope used in the United States 
is called grass rope, which is believed to be the fibre of the yucca, 
a kind of beards grass as it is called in this country. In fact, almost 
any tall vegetable that possesses great strength of fibre, may be 
manufactured into ropes. The Society for the Encouragement of 
Arts, &c. in London, have paid particular attention to this sub- 
ject, and by consulting the different annual volumes of their 
Transactions, it will be found that fine and strong thread and cloth 
may be obtained from the stems of the common stinging nettle and 
the bean, and that a coarse and strong material is yielded by the 
stalks of the hop plant, the bark of the lime tree, and several other 
vegetable productions. 

751. The value of these several materials depends, however, 
upon their strength and durability, and the changes that they 
undergo by being wet and dry, bent or straight, and under other 
casual circumstances; and after a fair trial and investigation of 
their several properties, good hemp appears superior to all that 
have so far been experimented upon. One of its valuable pro- 
perties is that its strength is not impaired by sudden bending, 
while if the aloe or grass rope are so treated, as in tying a knot, 
they loose their strength very considerably, unless previously 
steeped in water; and even then, are not so strong in the bent as 
in the straight parts. As hemp is the best known material, and 
has been more experimented upon than any other, we shall con- 
fine ourselves in the few observations to be made on this subject, 
to ropes of this material. 

752. When a number of small fibres are united together by 
the process of twisting or spinning, the thread so produced, what- 
ever may be the material, is called a yarn. Yarns may be made 
large or small, according to the purpose they are intended for. 
Thus all the varieties of sewing thread, however fine they may 
he, consist of at least two yarns spun or twisted together. But 
for rope making the yarn is much larger, and is generally about 
^th of an inch in diameter. In the British navy yards the size 
of hemp yarn is determined by its strength, for each separate yarn 
must be capable of supporting one hundred weight, and will there- 
fore be a little more or less in diameter, according to the goodness 
of the hemp. A rope is composed of a number of these yarns, 
usually from 16 to 25, twisted together, and this in large ropes is 
called a strand. Large ropes are never made immediately from 
the yarns, but by twisting two or more of these strands together. 
In the language of rope makers, three strands united, form a 



414 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

hawser; but when four are used, the rope is called a shroud. A 
cable is the union of three hawsers or three shrouds, and this large 
process of spinning is called laying a rope. 

758. By unravelling the end of a rope, the number of its com- 
ponent yarns may be readily discovered and counted, and as each 
yarn should bear 100 cwL, it may seem that this would offer a 
ready means of ascertaining the strength of new ropes. But the. 
very formation of a rope renders this impossible. If the fibres ran 
in right lined directions from end to end of the rope, it would give 
a near approximation to truth; but the twisting of the fibres to- 
gether makes the action an oblique, instead of a direct one; and 
thus, as those fibres near the centre of the rope, take a much 
straighter direction than those on its outside, all the violence of 
the strain will fall upon the central lines of fibres, while those on 
the outside will scarcely feel it at all. Taking the sum of the 
fibres or yarns, therefore, will give no clue to the strength of a 
rope as they are usually made; and no rope so made can possess 
a strength any thing like equal to what the sum of the yarns 
would produce or support if they could act singly. 

754. The late Captain James Huddart, of the British East 
India company's service, contemplating the imperfections to which 
large ropes were liable, from unequal or imperfect twisting, and 
the unequal strain to which the individual yarns were exposed in 
their common arrangement, invented a most admirable and sim- 
ple contrivance which he called a regulator, and for which he 
obtained a patent, by means of which ditTerent quantities of yarn 
was supplied to the different parts of the strand while it was twist- 
ing or laying. That yarn that went to form the centre of the 
strand, never deviated from its right lined direction, while a larger 
quantity was given out to the outsides which had to pass obliquely, 
and consequently through more space, and by this means, and 
using a less hard twist than had formerly been resorted to, he pro- 
duced the most perfect and uniform ropes, which were so perfect 
as to the equilibrium of their own parts, that they had no tendency 
to twist or recoil even when quite new; and on subjecting his 
ropes to experiment, it was found that instead of losing any of the 
original individual strength of the fibres, they assisted each other, 
and produced an aggregate power greater than their primitive 
one. Since the expiration of his patent, some of the principal 
rope-makers have adopted his plan of working, the advantages of 
which soon became known among nautical men. 

755. The tarring of ropes can evidently add nothing to the ab- 
solute strength of the materials of which they are formed; and 
yet it is thought to render ropes stronger. If it does so, it can be 
on no other principle than that the tar cements the fibres together, 



ON FORCE OP TENSION. 415 

and thus causes those parts to act conjointly, which without such 
assistance might have acted separately. The great use of tar is, 
however, to exclude moisture and prevent the rope from rotting, 
which it would do in damp situations; and it likewise prevents sand 
and grit getting into the inside of a rope, and these are very de- 
trimental to ropes that are kept in constant motion, as they fret 
and wear away the internal fibres. 

756. The rule that has been established by practice for ascer- 
taining the strength of new ropes made of the best hemp, without 
tar, is that they should support one-fourth of the square of their 
circumference taken in inches, in tons. Thus, if a rope is 2|: 
inches in diameter, its circumference may be taken at 9 inches, 
the square of which is 81 inches, and dividing this by 4, the quo- 
tient would be 201^ tons, which such a rope should bear upon a 
fair and even strain; but as all ropes are subject to jerks and con- 
cussions, it is better to take a fifth instead of a fourth of the square 
of the circumference, and this would reduce the above named rope 
to 16^ tons. Moreover as this rule applies to new ropes, made of 
the best material, and much inferior hemp is used, or cheaper 
materials of less strength are almost constantly mixed with it, and 
a rope is expected to last and wear a considerable time; so it is 
not prudent to put more than half this load upon a rope that is 
in constant use, because if strained to its full extent in the first 
instance, it will soon give way by use. 

The rule which Captain Huddart established in his rope manu- 
factory, and upon which he would warrant all ropes made there, 
was to multiply the square of the circumference of the rope by 
900, and this would give the number of pounds avoirdupois which 
the rope would sustain with safety. If we take the same exam- 
ple as before, of a rope having 9 inches circumference, then 9^= 
81 x900=32^ tons, or rather better than a third more than a rope 
of ordinary formation would bear. 

757. M. Du Hamel states that tarred rope is much weaker than 
that which is untarred, their diameters being equal, and he gives 
a table of comparative experiments made with three inch rope in 
proof of this assertion, in which the tarred rope is in every instance 
greatly inferior in strength to that without tar, but he assigns no 
reason for this apparent phenomenon, although it is well under- 
stood by every rope-maker. They usually demand the same price 
for tarred rope as for that which is clean, and even sometimes 
make a favour of charging nothing for the tar and trouble of ap- 
plying it. But the fact is, the tarring is always performed upon 
the separate yarns, by drawing them through a kettle of boiling 
tar, before they are twisted into strands. The hot tar swells the 
fibre, and a quantity of it adheres to each of them, so that the 



416 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

diameter of the yarn becomes sensibly increased, and of course a 
much less number of yarns become necessary to form a rope of 
the same diameter, than if clean hemp was used. This is quite 
sufficient to account for the deficient strength of tarred ropes; but 
if, instead of comparing the ropes by their diameters, they were 
compared by the number of yarns they contained, then the tarred 
rope would, it is believed, have the advantage. The inexperienced 
purchaser when he buys a tarred rope, does not usually consider that 
in each pound of rope he buys, he gets but about 14 oz. of hemp and 
2 oz. of tar, which are both sold for the same price, although hemp 
is at least sixteen times more costly than tar. M. Du Hamel, how- 
ever, goes on to state, that it is decided by experience that white 
cordage in continued service, is one-third more durable than 
tarred; that it retains its strength much longer while kept in 
store; and that it resists the ordinary injuries of the weather one- 
fourth longer. These observations deserve the attention of prac- 
tical men, being very important. There is, however, a reason 
why tarred ropes should be used in particular cases, such as the 
standing rigging of ships, or that which does not require to be run 
over pullies or to move; such as the main-stays, fore-stays, and 
shrouds, by which the masts of vessels are held and maintained in 
their vertical positions. The reason is that all untarred cordage 
(particularly when new) is highly hygrometric, and expands and 
contracts in its length to a great extent by being dry and wet. 
The damp state constantly producing contraction, and the dry 
one extension. This contraction by v/etting exercises so much 
force, that if a rope is fully stretched in its dryest state, and then 
wetted, it will break, or tear away the parts to which the ends 
are attached if they are less strong than the rope. If, therefore, 
a mast was braced in its proper position by dry white ropes, a 
shower of rain would probably bend the mast or break the ropes. 
On the contrary, if the mast was braced as tightly as possible by 
damp ropes, a few hours sunshine would render it quite loose. 
Any thing therefore that will destroy the hygrometric properties 
of the rope by rendering it less, or not at all absorbent of humidi- 
ty, will be beneficial in such cases; and tar or paint answer this 
purpose. This subject is worthy the attention of the Engineer, 
who will, in the course of his practice, frequently have to rig out 
temporary cranes or lifting apparatus for heavy stones, or masses 
of iron and timber, which are constantly supported by three or four 
guy ropes attached to the top of the apparatus, and drawing in 
opposite directions, the action being thus very similar to that on 
the mast of a ship. In the inclined planes that have been intro- 
duced into rail-roads, for surmounting considerable inequalities of 
level in the country they pass over, the cars or other loads are 



ON FORCE OF TENSION. 417 

drawn up, and let down the inclined plane by what is called an 
endless or perpetual rope, (as will be described when we arrive 
at that part of our subject,) and in these this expansion and con- 
traction is a source of great inconvenience and trouble; for as the 
rope must be kept constantly in a state of extension by passing 
over rollers at the top and bottom of the inclined plane, so it would 
inevitably become slack, or break, by contraction, with changes in 
the weather, unless some means was adopted for varying the dis- 
tance of the rollers from each other, according to the varying 
length of the rope; and this necessary motion becomes very con- 
siderable when the rope is long, as in the inclined plane of the 
Columbia rail-road, rising from the river Schuylkill close to Philar 
delphia,, and which being very nearly a mile long, requires a con- 
tinuous rope of two miles in length, to which the cars are attach- 
ed whenever necessary. 

758. Ropes are always sold and valued by weight, but are de- 
scribed by th6ir circumference in inches. Thus what is called 
a 3 inch rope would only be about 1 inch in diameter, and when 
a 24 inch cable is spoken of (being the largest size usually made), 
a cable less than 8 inches in diameter is understood. 

759. Strips of leather and raw hide are occasionally used for 
overcoming resistances instead of ropes; but of this we have few 
instances. They may be used with advantage in places that are 
usually dry, but do not answer well if exposed alternately to the 
wet and dry states. Strips of cow or horse skin leather, about 
four or five inches wide, sewed together in such manner as to 
form two thicknesses, and to break joint, or permit the joining of 
the two ends of every piece forming the one thickness, to come 
to the middle of the piece contiguous to it, are very commonly 
used to draw coals up the shafts of the coal mines of Staffordshire, 
and other internal parts of England; and they are said to be more 
economical than ropes, and to last much longer. But the great 
use that the Engineer makes of leather, is to form bands for driv- 
ing revolving machinery by means of large pullies or wheels 
called riggers, encompassed by such bands, and pulling them 
round by the mere friction exerted between the surfaces. Straps 
or bands employed in this way, are much more economical than 
toothed or cog-wheels, and are in many cases not only more con- 
venient, but produce a safer and more eflfectual action, particu- 
larly where heavy machinery has to be alternately put in motion 
and stopped. Thus a rotary motion can be communicated from 
one side of a mill to another by means of a strap or band, which 
could not be otherwise done, except by a long revolving shaft. 
The motion may be carried on in the same, or a reversed direc- 
tion, by carrying the strap directly round the riggers, or by 

53 



418 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

simply crossing the band; while a similarity of direction cannot 
be given by wheel-work without using three wheels. When 
motion is given to heavy machinery, or has to be stopped fre- 
quently, the inertia common to all matter frequently causes teeth 
or cogs to break off, because nothing can slide or give way; but 
if such motion is communicated by band-wheels, the band will 
slip over its wheels to a sufficient extent both at the beginning 
and end of the motion, to prevent the occurrence of any damage; 
and for these and other reasons that might be assigned, leather 
bands are well worth the attention of the Engineer. For small 
machinery, such as driving lathes, the governors of steam-engines, 
and such things as do not require much surface in the band to 
produce the necessary friction, catgut, or a string formed by 
twisting the intestines of animals in a wet state, and using them 
when dry, answers very well. This material in its state of great- 
est purity and perfection, is used for the strings of violins, harps, 
and other musical instruments; and if kept dry, is the strongest 
animal substance that can be formed. The power of a band for 
driving machinery, is increased by augmenting its width and the 
diameters of the drums or riggers over which it passes, thus offer- 
ing more surface for producing friction; and this is sometimes in- 
creased by occasionally chalking the surface of the drums, or ap- 
plying powdered rosin to them. 

760. The comparative strength of the materials generally used 
for forming bands for driving machinery, may be judged of from 
the following statement of the modulus of cohesion of each sub- 
stance, or the length in feet of a piece of the same magnitude that 
would be required to overcome its cohesion, or tear it asunder, 
as calculated by Mr. B. Bevan, an English Engineer, and pub- 
lished by Dr. 0. Gregory.* 



Tanned Cow's skin feet 10,250 

„ Calfskin 5,050 

„ Horse skin 7,000 

,, Sheep skin 5,600 



Tanned Cordavan leather feet 3,720 

Untanned Horse skin 8,900 

Hempen Twine 75,000 

Catffut, old 23,000 



"-&" 



The strength of adhesion produced by nails, screws, and glue. 

761. Every carpenter is aware of the mode of applying these 
materials, and of the advantages derived from them; but until 
lately this subject has never been experimented upon or examin- 
ed with any degree of accuracy, and we are now indebted to Mr. 
Bevan, above mentioned, who is the only person who appears to 
have paid attention to this subject. He has tried many experi- 

* Gregory's Mathematics for Practical Men, p. 411. 



ON THE STRENGTH OF ADHESION. 



419 



ments with great care and attention, the result of which he has 
communicated to the public through the medium of the Philoso- 
phical Magazine, in which work he has several papers, all show- 
ing the accuracy with which he has investigated this new sub- 
ject, and the attention he has paid to it. 

762. Mr. Bevan observes, that the theoretical investigation 
points out an equality of i-esistance to the entrance and extraction 
of a nail, supposing its thickness to be invariable; but as the gene- 
ral shape of nails is tapering towards the point, the resistance of 
entrance necessarily becomes greater than that of extraction. In 
some instances he found the ratio to be as 6 to 5. 

The following table exhibits the relative adhesion of nails of 
various kinds, when forced into dry Christiana deal at right angles 
to the grain of the wood. 



Description of nails used. 


Number of 

nails to the 

lb. avoir. 


Length of 
nails in 
inches. 


Inches 
forced into 
the wood. 


Pounds 
requisite 
to extract. 


Fine sprio;s 


4560 


0.44 


0.40 


22 


Do. 


3200 


0.53 


0.44 


2>7 


Threepenny brads 
Cast Iron nails 


618 
380 


1.25 
1.00 


0.50 
0.50 


58 

72 


Sixpenny nails 
Do. 


7^ 


2.50 


1.00 
1.50 


187 
327 


Do. 


—. 




2.00 


530 


Fivepenny nails 


139 


2.00 


1.50 


320 



763. The percussive force required to drive a common sixpenny 
nail to the depth of one inch and a half into dry Christiana deal, 
with a cast iron weight of 6.275 Ihs., was four blows or strokes 
falling freely the space of 12 inches: and the steady pressure to 
produce the same etfect was 400 lbs. 

764. A sixpenny nail driven into dry elm to the depth of one 
inch, across the grain, required a force of 327 lbs. to extract it: 
and the same nail driven endways, or longitudinally into the same 
wood, was extracted with a force of 257 lbs. The same nail 
driven two inches endways into dry Christiana deal, was drawn 
by a force of 257 lbs. To draw out one inch, under like circum- 
stances, took 87 lbs. only. The relative adhesion, therefore, in the 
same wood, when driven transversely and longitudinally, is 100 to 
78; or about 4 to 3 in dry elm; and 100 to 46, or 2 to 1 in deal: 
and in like circumstances the relative adhesion of elm and deal, 
is as 2 or 3 to 1. In other species of wood, the requisite force to 
extract nails was different. Thus, to extract a sixpenny nail from 
a depth of one inch, out of dry oak, required 507 /6s.; from dry 
beech 667 lbs.; and from green sycamore 312 lbs. 



420 ON THE ABSOLUTE STRENGTH OP MATERIALS. 

765. From these experiments we may infer that a common six- 
penny nail driven two inches into dry oak, would require a steady 
force of more than half a ton to extract it. Nails that are slightly 
rusty, hold much more strongly than such as are quite new and 
clean. Millrights, therefore, frequently steep their new nails in a so- 
lution of crude sal ammoniac, to induce this effect, and drive them 
into the wood in their wet state where great adhesion is required. 
This is unnecessary in oak, unless it is very dry; because the natu- 
ral juices of oak will always rust iron that is driven into it. 
Wrought iron nails hold more firmly than the cut nails now in 
general use, owing probably to the cut nail being more right lined 
and smooth on the surface than such as are produced by the ham- 
mer; for all nails hold merely by the compression that exists be- 
tween themselves and the wood. Large nails are called spikes^ 
and these are sometimes jagged on their angles to increase the 
friction and adhesion, and then they approach the nature of 
screws; for a screw holds faster than a nail, because its thread 
enters into, and lays hold of the substance of the wood; conse- 
quently, a screw cannot be drawn by a direct force, without tear- 
ing away part of the wood into which it has been introduced, and 
thus the adhesion produced by screws, is always much greater 
than that of nails. 

766. Glue is a well known material, and one that is extensively 
used by the cabinet-maker and joiner for fastening pieces of wood 
together. It is obtained by digesting the skins, hoofs, and other 
parts of animals a long time in hot water, straining the liquid to 
deprive it of impurities and solid matter, and then further evapo- 
rating the water until the residuum becomes of a proper consistence 
for use. Glue when in a thin and gelatinous state while cold, is 
the size that is extensively used by painters and paper-hangers; 
consequently, this size, which is not procurable out of large towns, 
may be made at any time by dissolving glue, and diluting^ the so- 
lution with hot water. Glue is sold in thin cakes which are semi- 
transparent, and very hard while dry. In this state glue will 
keep any length of time without injury to its qualities. The 
greatest inconvenience of glue is its solubility in water; conse- 
quently, it cannot be used for outside woodwork, or even for in- 
side work that is subject to wet or damp, unless such work is 
painted in oil, or varnished to protect it, and then it will stand 
many years. To obtain the greatest strength from glue, it ought 
to be recently dissolved, and used soon afterwards; for glue that 
has been heated and cooled, and kept a long time, as in a common 
carpenter's glue pot, is more brittle, and does not hold so strongly as 
that which is recently made. Isinglass is the best and purest glue, 
and this is made from the gelatin of certain fish, instead of from 



ON THE STRENGTH OF ADHESION. 421 

animal substance. It is as soluble as other glue in water near the 
boiling point, but has the advantage of being insoluble, or nearly 
so, in cold water. Hence joints made with this glue will not be 
affected by the humidity of the atmosphere for want of sufficient 
heat, and it is on this account always used by the makers of 
violins and such other musical instruments as are put together by 
glue alone. 

767. To obtain the greatest strength or adhesion in a glued 
joint, the wood to which it is applied should be slightly absorbent, 
and the surfaces made to fit together as closely as possible, before 
the glue is applied. These surfaces should be smooth, but not 
polished, and they nnust be perfectly clean, or free from grease 
or any resinous matter, on which account surfaces of yellow pine 
will not glue together with any certainty of firmness. The glue 
must be free from all dirt or grit, which would prevent close con- 
tact, and should be so far diluted with water that it will just run 
freely, and wet, and .sink into the surface to which it is applied, 
and it should be as hot as possible at the time. Both the surfaces 
should, if possible, be covered with glue; if not, and the joint is 
straight, the edge of one board may be rubbed upon the other 
that has received the yet fluid glue, until both surfaces are cover- 
ed, and the superfluous glue is squeezed out of the joint, when a 
very considerable pressure should be instantly applied by imple- 
ments called glueing screws, or by the application of wedges, to 
press out the glue, and bring the two surfaces into as close con- 
tact as possible; and this done, the joint should be set by, under 
the pressure, and not be touched for several hours, or until the 
glue is quite cold, and all the water it previously contained has 
had time to dry away. The time required will therefore depend 
on the state of the atmosphere at the time, or the temperature of 
the place in which the work remains. A well made glued joint 
in dry wood w-ill in this way be found as strong, and in some cases 
stronger than the wood itself. Glue will produce the adhesion of 
woods, leather, paper, and all things that are absorbent; but it 
cannot be applied to unite metals, or wood and metals, glass, porce- 
lain, or hard stones, because these are not absorbent, and the glue 
cannot attach itself to their surfaces. To unite them, mortar, 
plaster of paris, putty, white-lead ground in oil, or resinous cements, 
formed by melted rosin, shell-lac, wax, or such kind of materials 
must be resorted to. 

768. Mr. Be van, before referred to, is the only person who has 
published the results of any experiments on the adhesive strength 
of glue. He glued together by the ends, two cylinders of dry ash 
wood, of an inch and a half in diameter, and about 8 inches long. 
After having been glued 24 hours, they required a direct force of 



422 ON THE ABSOLUTE STRENGTH OP MATERIALS. 

1260 lbs. to separate them; and as the area of the circular ends of 
the cylinders were 1.76 inch, it follows that the force of 715 lbs, 
would be required to separate one square inch. This experiment 
was made with new glue, dissolved for the purpose, and on repeat- 
ing it several times with glue that had been frequently heated, 
and to which additions, both of glue and of water, had been often 
made, he obtained a result of from 350 to 560 lbs. to the square 
inch. In these experiments the force was applied gradually, and 
perpendicularly to the centres of the surfaces glued together. The 
force was generally sustained for two or three minutes before the 
separation took place. On examining the surfaces after their 
separation, the coat of glue appeared to be very thin, and did not 
adhere over the whole surface of the wood; so that the actual ad- 
hesion of glue must be something greater than 715 lbs. to the 
square inch. 

769. Mr. Bevan also tried the lateral cohesion of a piece of dry 
and well seasoned Scotch fir, or pine board, and found that it re- 
quired 562 lbs. to the square inch to divide it; consequently, if 
two pieces of this wood should have been glued together, the wood 
would have yielded in its substance before the glued joint. 

770. From a subsequent experiment made on solid dry glue, its 
cohesive force was found to be 4000 lbs. to the square inch; from 
which it may be inferred that the application of glue as a cement 
does not give so large a result as might be expected, and that the 
method of using it is defective, and susceptible of improvement. 

Of the force of Torsion. 

771. The only subject remaining to be noticed in the present 
section, and with which we shall close it, is the resistance that 
a shaft or axis offers to a force applied to twist it round, and this 
is called the force, or resistance of torsion. This force is in the 
nature of a lever, revolving about the axis or central line of the 
shaft, and is so considered and investigated by Mr. Tredgold. Pro- 
fessor Robison on the contrary, views the shaft as a series of con- 
centric tubes placed one within the other. The demonstrations 
and examples given by Mr. Tredgold, are so extensive, as to pre- 
clude their being admitted wholly in this place, and the student is 
therefore referred to them,* and ample directions will be found 
applying to most shapes and materials in practice. Professor 
Robison's observations are more g^eneral and concise, and are, 
therefore, adopted in our present explanations.! 

* Essay on Strength of Cast Iron, Section 9, p. 215. 
t Robison's Mechanical Philosophy, Vol. I., p. 488. 



OF THE FORCE OF TORSION. 423 

772. He observes, we cannot have a very distinct conception 
of that modification of the cohesion of a body by which it resists 
this kind of strain; but there can be no doubt, that when all the 
particles act alike, the resistance must be proportional to their 
number. Therefore, if we suppose the two parts abed, ah fe 
(Fig. 141, PI. V.) of the body efc d, to be of insuperable strength, 
but cohering more weakly in the common surface a b, and that 
one part a b c d is pushed laterally in the direction a b, there can 
be no doubt hut it will yield only there, and that the resistance 
will be proportional to the surface. 

773. In like manner, we may conceive a thin cylindrical tube, 
of which KAH, Fig. 142, is the section, as cohering more weakly 
in that section than any where else. Suppose it to be grasped in 
both hands, and the two parts twisted round the axis in opposite 
directions, as we would twist the two joints of a flute, it is plain 
that it will first fail in this section, which is the circumference of 
a circle, and the particles of the two parts that are contiguous to 
this circumference, will be drawn from each other laterally. The 
total resistance will be, as the number of equally resisting parti- 
cles; that is, as the circumference (for the tube being supposed 
verv thin, there can be no sensible difference between the dilata- 
tion of the external and internal particles). We can now sup- 
pose another tube within this, and a third within the second, and 
so on till w^e reach the centre. If the particles of each ring ex- 
erted the same force (by suffering the same dilatation in the direc- 
tion of the circumference), the resistance of each ring of the sec- 
tion would be as its circumference and its breadth, (supposed 
indefinitely small,) and the whole resistance would be as the 
surface, and this would represent the resistance of a solid cylinder. 
But when a cylinder is twisted in this manner by an external force 
applied to its circumference, the external parts will suffer a 
greater circular extension than the internal; and it appears that 
this extension (like the extension of a beam strained transversely), 
will be proportional to the distance of the particles from the axis. 
We cannot say that this is demonstrable, but we can assign no 
proportion that is more probable. This being the case, the forces 
simultaneously exerted by each particle, will be as its distance from 
the axis. Therefore, the whole force exerted by each ring, will be 
as the square of its radius; and the accumulated force actually 
everted, will be as the cube of the radius; that is, the accumulat- 
ed force exerted by the whole cylinder, whose radius is CA, is to 
the accumulated force exerted at the same time by the part whose 
radius is CE, as CA^ is to CE'. 

The whole cohesion now exerted, is just two-thirds of what it 
would be, if all the particles were exerting the same attractive 
forces which are just now exerted by the particles in the external 



424 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

circumference. This is plciin to any person fanniliar with the 
fluxionary calculus, and such as are not nnay easily see it in the 
following way. 

Let the rectangle ACca, Fig. 142, be set upright on the surface 
of the circle, along the line CA, and revolve round the axis Cc, 
it will generate a cylinder whose height is Cc, or Aa, having the 
circle KAH for its base. If the diagonal Ca be supposed also to 
revolve, it is plain that the triangle cCa will generate a cone of 
the same height, and having for its base the circle described by 
the revolution of c a, and the point C for its apex. The cylindri- 
cal surface generated by Aa, will express the whole cohesion ex- 
erted by the circumference AHK, and the cylindrical surface 
generated by Ee will represent the cohesion exerted by the cir- 
cumference ELM, and the solid generated by the triangle CAa 
wdll represent the cohesion exerted by the w^hole circle AHK, and 
the cylinder generated by the rectangle AC ac, will represent the 
cohesion exerted by the same surface, if each particle had suffer- 
ed the extension Aa. 

Now it is plain, in the first place, that the solid generated by 
the triangle eEC is to that generated by aAC as EC^ is to AC^. 
In the next place, the solid generated by aAC is two-thirds of the 
cylinder, because the cone generated by cCa is one-third of it. 

774. We may now suppose the cylinder twisted till the par- 
ticles in the external circumference lose their cohesion. There 
can be no doubt that it will now be wrenched asunder, all the 
inner circles yielding in succession. Thus we obtain one useful 
piece of information, viz: that a body of homogeneous texture re- 
sists a simple twist with two-thirds of the force with which it resists 
an attempt to force one part laterally from the other, or with one- 
third part of the force that will cut it asunder by a square edged 
tool. For to drive a square edged tool through a piece of lead, 
for instance, is the same thing as forcing a piece of the lead as 
thick as the tool laterally away from the two pieces on each side 
of the tool. Experiments of this kind do not seem difficult, and 
they would give very useful information. 

775. When two cylinders AHK and BNO, Fig. 142, are wrench- 
ed asunder, we must conclude that the external particles of each, 
are just put beyond their limits of cohesion, are equally extended, 
and are exerting equal forces. Hence it follows, that in the in- 
stant of fracture, the sum total of the forces actually exerted, arp 
as the squares of the diameters. For drawing the diagonal Ce, it 
is plain that 'Ee=Aa, expresses the distension of the circumfer- 
ence ELM, and that the solid generated by the triangle CEe, ex- 
presses the cohesion exerted by the surface of the circle ELM 
when the particles in the circumference suffer the extension Ee 



ON THE FORCE OF TORSION. 425 

equal to Aa. Now the solids generated by CA«, and CEe, being 
respectively two-thirds of the corresponding cylinders, are as the 
squares of their diameters. 

776. Having thus ascertained the real strength of the section, 
and its relation to its absolute lateral strength, we must next ex- 
amine its strength relative to the external force employed to break 
it. This examination is very simple in the case under considera- 
tion. The straining force must act by some lever, and the cohe- 
sion must oppose it by acting on some other lever. The centre of 
the section may be the neutral point whose position is not dis- 
turbed. 

Let F be the force exerted laterally by an exterior particle. 
Let a be the radius of the cylinder, x the indeterminate distance 

of any circumference, and x the indefinitely small interval between 

the concentric laminae or arches; that is, let x be the breadth of 
a ring, and x its radius. The forces being as the extensions, and 
the extensions as the distances from the axis, the cohesion actually 

exerted at any part of any ring will bey* — " . The force exert- 

ed by the whole ring (being as the circumference, or as the 

X X 

radius), will hef . The momentum of cohesion of a ring, being 

^ 3 * 

as the force multiplied by its lever, will be/ — . Th^ accumu- 



lated momentum will be the sum or fluent of/ j that is, when 

a 
a* 
x=a it will be i / — ,=^f a^- 



a 



777. Hence we learn that the strength of an axle or shaft, by 
which it resists being wrenched asunder, by a force acting at a 
given distance from the centre line or axis, is as the cube of its 
diameter. 

But farther, J/a^ is =zfa^Xia. Now/a^ represents the full 
lateral cohesion of the section. The momentum, therefore, is the 
same as if the full lateral cohesion was accumulated at a point 
distant from the axis by Jth of the radius, or |th of the diameter 
of the cylinder. Therefore, let F be the number of pounds which 
measures the lateral cohesion of a circular inch, d the diameter 
of the cylinder in inches, and I the length of the lever, by which 
the straining force p is supposed to act, we shall have 

d^ 
Fx^d^=p I, and F -^=p* 

54 



426 ON THE ABSOLUTE STRENGTH OF MATERIALS. 

We see in general that the strength of an axle, by which it re- 
sists being wrenched asunder by twisting, is as the cube of its 
diameter. 

778. We see also that the internal parts of an axle do not act 
as powerfully as the external. If a hole be bored out of the mid- 
dle of an axle, equal to half its entire diameter, the strength is 
diminished only one-eighth, while the quantity of matter is dimin- 
ished one-fourth. Therefore hollow axles are stronger than solid 
ones containing the same quantity of matter. Thus let the diame- 
ter be 5, and that of the hollow 4; then the diameter of another 
solid cylinder, having the same quantity of matter as the tube, 
will be 3. The strength of the solid cylinder of the diameter 5 
may be expressed by 5^ or 125. Of this, the internal part having 
the diameter of 4, exerts 64; therefore the strength of the tube is 
125 — 64,^61. But the strength of the solid axle of the same 
quantity of matter, and diameter 3, is 3^ or 27, which is not half 
that of the tube. 

779. Engineers, therefore, have of late, since cast iron has been 
so extensively used, introduced this improvement into their ma- 
chines, by making all cast iron shafts and axles hollow, when their 
size will admit of it. They have the additional advantage of 
being much more stiff and free from vibration; while at the same 
time much metal is saved, by which they are lighter on their bear- 
ings and pgaduce less friction; and what is most important is, that 
they are less costly, and more certain in their daration; because 
large solid castings are likely to be defective in their internal parts, 
for reasons that have been before explained. (618.) 

780. Professor Robison states, that when the matter of the 
axle is of the most simple texture, such as that of metals, he does 
not conceive that its length has any influence on its fracture; but 
it is otherwise in fibrous materials like timber, for then the fibres 
are bent or twisted into spirals like a corkscrew before breaking. 
The length of the axle in this case has somewhat the influence of 
a lever, and will be easier wrenched asunder if long, than short; 
but he has not been able to reduce this influence to calculation. 
Experience, however, proves that long shafts or axles, whether of 
iron or of wood, are more easily broken than short ones; and, there- 
fore, as a practical rule, all shafts should be kept as short as pos- 
sible, or the nature of the place where they are used will admit 
of. AH shafts, whether of wood or metal, will twist to a certain 
extent in working, from the natural elasticity of their materials; 
and this twisting may be permitted, and is not detrimental to their 
action, provided it does not go so far as to disturb the natural ar- 
rangements of their particles, or produce jumps and jerks in the 
work. 



ON THE FORCE OF TORSION. 427 

781; The quantity of twisting that is thus inevitable, is called 
thea?igle of torsion, and Mr. Tredgold observes, that if it is under 
two degrees in a cast iron shaft, it need not be regarded, but it 
should never exceed this quantity. In wooden shafts it is fre- 
quently more considerable. He gives rules and their demonstra- 
tions at greath length in his excellent work on the Strength of 
Iron, for determining the strength of shafts, and from these the 
three following examples have been selected. 

782. Rule I. To determine the diameter of a solid cylindrical shaft v 
of cast iron to resist torsion, with a given flexure. 

Multiply the power in pounds, by the length of the shaft in (eet, 
and this by the leverage with which the power acts. Divide this 
product by 55 times the number of degrees in the angle of torsion, 
which is considered best for the action of the machine; and the 
fourth root of the quotient will be the diameter of the shaft. 

Example. 

Let it be required to find the diameter for a series of lying shafts 
30 feet in length, to transmit a power of 4000 lbs., acting at the 
circumference of a wheel of 2 feet radius, so that the twist of the 
shafts on the application of the power, may not exceed one 
degree? 

Here the whole length must be taken as if it were one, shaft, 
and by the rule lbs. ft. ft. 

4000x30x2 __^gg^ 
55X1 

Then by a Table of Powers,* or the ordinary process of work- 
ing, find the fourth root of 4364, which is 8.13 inches, the diame- 
ter required. 

783. If the machinery be required to act with much precision, 
this will be as much flexure as can be allowed; but in ordinary 
cases, two degrees might be admitted, and then the diameter of 
the shaft would be rather less than 7 inches. Where there is 
much wheelwork, the flexure should be less. In accurate work 
it is not desirable to allow the shaft or axles to exceed a quarter 
of a degree. 

784. Rule II. To determine the diameter of a hollow cylinder to 
resist torsion, when the thickness of metal is one-fifth of the diameter, 
and the flexure is given. 

Multiply the length of shaft, the power, and its leverage into 
each other, as in the last case; and divide the product by 48 times 
the angle of flexure in degrees; the fourth root of the quotient 
will be the diameter required in inches. 

* See Barlow's Mathematical Tables— Table III. 



428 on the absolute strength op materials. 

Example. 

Required the diameter of a hollow shaft 10 feet long, that may 
be sufficient to withstand a force of 800 /65., acting at the circum- 
ference of a wheel of 4 (eet radius; the flexure not to exceed one 
degree, and the thickness of metal to be one-fifth of the diameter? 

800x10x4 

In this case — ; — =666.6 the 4th root of which is 5.1 

48X1 

inches nearly, being the diameter required. The hollow through 

the middle of this shaft, would therefore be 3 inches, thus leaving 

the metal about one inch thick all round, or |^th of the diameter 

which experience as well as demonstration points out to be the 

best proportion for the thickness of metal in hollow shafts. 

785. Rule III. To determine the side of a solid square cast iron 
shaft to resist torsion, with a given flexure. 

Multiply the length of the shaft, the power, and its leverage 
into each other as before; and divide the product by 92.5 times 
the angle of flexure in degrees, and the square root of the quotient 
will be the ai-ea of the shaft in inches. 

Example. 

The length of the shaft is 12 feet; it is to be driven by a power 
of 700 lbs» acting on a pinion on the shaft of one foot radius to the 
pitch line; the flexure not to exceed one degree. 

By the rule — — — — - — =90.8 the square root of which is 9.53, 
9.4. o XI 

the area of the section in inches; and the square root of 9.53 is 3.1 

inches nearly, for the breadth of one side of the shaft. 

Section III. Of the relative strength of Materials,* 

786. By the relative strength of materials is meant, the strength 
or resistance they are capable of offering when placed in such 
positions, or under such circumstances, as will not permit their 
actual or absolute strength, as before explained, to be fully exer- 
cised; or the relation of their absolute strength, to that which they 
may be able to exert under the particular circumstances by which 
they are constrained to act. The actual or absolute strength of a 
body cannot be changed or augmented in any way while the body 
remains the same, but it may be diminished by position and other 
causes; and in considering the nature of this force, we shall have 
frequent occasion to refer to what has been already stated; be- 

* Chiefly compiled from Professor Robison's Mechanical Philosophy, Dr. 
Young's Lectures on Natural Philosophy, Hutton's Mathematics and Gregory's 
Mechanics, 



OF THE RELATIVE STRENGTH OF MATERIALS. 429 

cause the actions of compression, extension, and torsion, are often 
in operation at the same moment. 

787. What is meant to be implied by relative strength, and the 
difference between it and absolute strength, will, it is believed, 
be better understood by an example than by description. Thus 
suppose a beam or piece of wood a b, Fig. 143, to be supported 
under its two ends by brick walls, as is the case in the girder of a 
floor of any ordinary building. Such a beam, if long and per- 
fectly straight before it is so placed, will inevitably swag or sink 
downwards in its central part c by its own weight. But if we 
further suppose the floor to be loaded with furniture, persons, or 
any additional load, which may be represented by a heavy iron 
ball d, the beam will suffer a further bending, or may even be 
broken in two. The same thing will occur, w^hether the weight 
d be applied above the floor, or is hung or appended below it as 
at e. If now, we suppose either of these weights to be divided 
into 5 or any other number of smaller weights, the sum of 
which shall be equal to the large one, and that they shall be 
ranged at equal distances from each other, the beam will evidently 
have the same weight to sustain, and yet it will not sw^ag or yield 
to the same extent, but will appear to have more strength to re- 
sist the distributed load, than the one that is concentrated upon 
its centre. The strength or resistance in one case, will therefore 
be relative towards that in the other, and there will be a relation 
between these strengths and that of the beam when not loaded 
at all; and as these strengths or powers of resistance are all dif- 
ferent, it is clear that they cannot agree with the absolute or 
actual cohesive strength of the beam which is immutable: neither 
will they agree with either of the strains before discussed; for a 
strain of compression would tend to bring the ends a and 6, or the 
sides d and e into a state of closer approximation; while a strain 
of extension would have the directly opposite effect. 

788. Supposing the beam to break under the influence of its 
load; if we examine what takes place, it will»be found that the 
fracture or opening will commence at the bottom or under side of 
the beam, and will proceed upwards in as nearly a perpendicular 
direction as the fibres of the wood will permit; but that no chasm 
or opening will appear at the top of the beam. In some cases, a 
separation of parts will not even occur; but the top surface, though 
much bent, may hang together by its fibres. A different action 
must therefore have taken place at the top and the bottom of the 
beam, and such really is the case; for some fulcrum or resisting 
part must exist in the beam, to produce the opening or fracture 
on the under side. That is brought about by an extending force, 
but the reaction to produce that extending force, is in the upper 



430 OF THE RELATIVE STRENGTH OF MATERIALS. 

part of the beam, which therefore suffers compression; consequent- 
ly, all the part of the beam under the point c will be extended, 
and all above it compressed, the two forces being in operation at 
the same instant. These two forces exist to the greatest extent 
at the top and bottom of the beam, diminishing gradually towards 
the centre, where they change into each other; and at this place, 
therefore, the forces are neutral, or diminish to nothing. This 
neutral position will extend quite across the beam at right angles 
to the direction of the applied force, and is called the axis of frac- 
ture. 

789. It matters not whether the force that produces this bend- 
ing or fracture is applied above or below, or to one side or the 
other of the beam, since its operation will be alike in all cases, 
except so far as it is increased or decreased by the weight of the 
beam itself; therefore such a force is called a lateral force, and as 
its effects are influenced by other circumstances besides the posi- 
tive strength or cohesion of the material, the resistance to its 
action is called the stiffness of materials to distinguish it from their 
strength. Strength being the power they possess to resist fracture 
or breaking; and stiffness the power to resist flexure or bending. 

790. We have taken as an example, a beam supported at both 
its ends; but if one end was built into a solid wall, so as to be 
firmly supported, while the other projected beyond it, and was 
unsupported, and a load should be applied to this end, or to any 
other part of the projection, its stiffness would be called into ac- 
tion, but under different modifications. The object of this section 
will therefore be to examine a few of the most common cases 
that occur in practice, and to point out the means of obtaining 
the greatest quantity of strength with the least quantity of mate- 
rial, an object that the Engineer should always keep in view, 
because the greater the quantity of material, and the greater 
will be the cost of the work, which will be considerably enhanced 
by the time and workmanship necessary to convert and put it 
together. • 

791. This subject is of such vast practical importance, that it 
has been much written and experimented upon, and has occupied 
the attention of many of the first philosophers and mathemati- 
cians, among whom may be mentioned Gallileo, Mariotte, Leibnitz, 
Euler, Bernoulli, Lagrange, Emerson, Hutton, Girard, Robison 
and Young; and more might be said on this subject alone, than is 
intended to fill the whole of the present volume; for under our 
limited extent, all that can be attempted, is to give the student 
a general outline of what has been done, and to direct his atten- 
tion to such points as it is believed will be most useful to him. 
For particulars he must tefer to the works that have appeared 



OF THE RELATIVE STRENGTH OP MATERIALS. 431 

on this and other subjects, and those already noticed with Tred- 
gold's Elementary Principles of Carpentry, will be found replete 
with useful information. 

792. Let us in the first place examine the effects that would 
occur if a rectangular piece of plank k Imrij Fig. 144, should be 
firmly built into a brick wall as at k m o p, in such manner that 
the end so built in shall be incapable of motion; but that the 
other end o I p n may project into open space without any other 
support than the cohesion of its own particles, which unite it to 
the part built into the wall; and moreover, that a weight w shall 
be suspended from the point n. It will be evident that the 
weight of the projecting end of the plank added to that of the 
weight w, will constitute a force that will tend to break and de- 
press it; and if it was equally strong in every part, but very 
brittle, it ought to break off in the direction of the dotted line op, 
and descend perpendicularly by the moving surface at op, sliding 
downwards over the corresponding fixed surface. Such an effect 
would, however, be prevented in almost every case by the fibrous 
nature and cohesion of the parts of the plank, which would pre- 
vent its breaking so abruptly and sliding downwards; and in al- 
most every case the projecting end o I pn would become curved by 
being bent downwards at its end/ n; and as the pointp close to the 
wall is supported, that point may be conceived to be the centre 
or fulcrum, upon which the first bending would take place, and 
the wood near p would be in a state of compression, while the 
whole upper surface o I would be subject to a force of extension. 
Hence, in such a case, the fracture or breaking would always 
commence at the top of the beam, and would proceed downwards 
in a direction as nearly perpendicular as the texture of the sub- 
stance would permit. The strength of such a beam would, there- 
fore, depend mainly on the direct cohesion of its parts near o, to 
resist such separation; but still this case is quite different from 
those examined under the head of extending forces, in which the 
weight or power to produce separation was acting with its own 
unmodified force, in the direction of the axis, or length of the 
piece; and, consequently, would exert an equal power on every 
particle in the transverse section where the fracture occurred. 

In this case the action is neither equable over the whole sec- 
tion, nor is it directly as the power of the weight or force employ- 
ed; but is of a more complex nature, because a bent lever is pro- 
duced, in which the supported point p is the fulcrum, the line 
p n is the acting arm, or represents the force with which the 
weight can act to produce fracture, and the line p o will be the 
resisting arm, or measure of the force that can resist fracture; and 
in proportion as the line p 7i is longer than the line p o, so will the 



432 OP THE RELATIVE STRENGTH OP MATERIALS. 

weight w have a greater power to break the projecting timber; 
so that if we conceive this piece to be cut horizontally to half its 
former depth by the line r s, then r s will be equal to p n, so that 
the power of the weight remains the same; but r o is only the 
half of ^ 0, consequently the weight will leave twice the power 
to produce fracture; while, if ;? o should be increased in depth, it 
will bear a larger proportion to p n, and will therefore be stronger. 
Depth, or distance from top to bottom, in beams of this kind, there- 
fore, increases their strength; while the thickness may remain the 
same. 

793. We see likewise in this example that the fracture must 
occur at the place o p near the wall; because all other things 
remaining the same, if we assume any other point v in the bottom 
of the beam as the fulcrum, then v n will be the acting arm, and 
V t the resisting arm of the lever, and they are equal: but p n'ls 
four times as long as v w, while p o is equal to v t; therefore (inde- 
pendently of the weight of the timber) the weight w will have 4 
times as much power at o as it has at t; and consequently the 
fracture will take place at op. For the same reasons increasing 
the length of the piece o Ip n, while its area remains the same, 
will diminish its strength, because this is increasing the arm jo n, 
while p remains unaltered. A piece of timber, or other material, 
may therefore be so extended as to break by its own weight, or 
without the assistance of any weight w applied to it. 

794. In examining cases of fracture by direct extension, the 
cohesive force of all particles in the cross section is considered 
equal, and these forces will, in fact, be also equal in the plane of 
fracture that takes place from a lateral strain, like the beam pro- 
jecting from a wall just spoken of; yet, in practice, they are not 
equal, or rather, although they are really equal, they are acted 
upon by different degrees of force in different parts of the beam, 
and this produces the same effect as if they were unequal. That 
this operation is unequal will be rendered manifest by recurrence 
to the last figure, in which we may conceive the transverse sec- 
tion p to he composed of a line or series of particles infinitely 
near to each other, and all possessing equal cohesive power. But 
as the arm of the lever p n remains of uniform length, the weight 
w will act with diminished power on every particle as they suc- 
ceed from p towards o, and the power of the weight at o to sepa- 
rate two particles horizontally, will be only half as great as it will 
be at r, and will diminish while it proceeds upwards from o, and 
will increase downwards to jo, where it will be greatest of all. 
Notwithstanding, therefore, that the cohesion may be equal in 
every part of the beam, that beam will be weaker in effect below 
r than above it, because the force tending to produce rupture in 



OF THE RELATIVE STRENGTH OP MATERIALS. 433 

that part, is greater than it is above. Still the parts near r, ren- 
dered weaker by this effect, will be strengthened and sustained by 
the upper parts near o, because they have more power to resist 
separation; and it will therefore appear that if a fracture begins 
near o, by which the sustaining power of those parts are abstracted, 
the beam must inevitably break off, from the less favourable posi- 
tion of the lower particles to resist the strain. 

795. This is a case that requires the aid of the fluxionary cal- 
culus for its investigation, but Professor Robison puts it in a very 
simple form,* by supposing the beam instead of projecting from a 
wall, to be hanging from the ceiling, in which it is firmly fixed, 
and then considering how the equal cohesion of every part operates 
in hindering the lower part from separating from the upper by 
opening round the joint p. The equal cohesion operates just as 
equal gravity would do, but in the opposite direction. Now we 
know that the effect of this will be the same as if the whole weight 
was concentrated in the centre of gravity r of the line o p, and 
that this point r is in the middle of o jo. Now the number of fibres 
being at the length of the line o p may be represented by D, and 
the cohesion of each fibre being =F, the cohesion of the whole 
line will be FxD, or FD. 

The acumulated energy, therefore, of the cohesion in the in- 
stant of fracture is, FDx^D. Now this must be equal or just infe- 
rior to the energy of the power employed to produce fracture. 
Let the length of the beam jo n be called L, and the weight w, W; 
then WxL is the corresponding energy of the power. This gives 
us FD|^D=PL for the equation of equilibrium, corresponding to 
the vertical section ol p n. 

796. Suppose now that the fracture is not permitted at op, but 
at another section s more remote from n. The body being 
prismatic all the vertical sections are equal; therefore FD-JDis 
the same as before. But the energy of the power is by this means 
increased, being now=i7:uXwcr, instead of zoXn p: hence we see 
that when the prismatic body is not insuperably strong in all its 
parts, but equally strong throughout, it must break close to the 
wall, where the strain or energy is greatest. We see too, that a 
power which is just able to break it at the wall, is unable to 
break it at a distance from that wall; because although an abso- 
lute cohesion FD, which can withstand the power W in the sec- 
tion p, will not be able to withstand it at /2 ^, and will withstand 
more in any external section, as ^ ??. 

797. This teaches the distinction between absolute and relative 
strength. The relative strength of a section has a reference io 

* Robison's Mech. Philos., Vol. I. p. 415. 
55 



434 OP THE RELATIVE STRENGTH OF MATERIALS. 

the strain actually exerted on that section, and is properly mea- 
sured by the power which is just able to balance or overcome it 
when applied at its proper place. Now since we had FD -i D= WL, 

FDiD 
we have W= — p — ■ for the meausure of the strength of the 

section op in relation to the power applied at zo. 

798. If the solid is a rectangular beam, whose breadth is B, all 
the vertical sections will be equal; consequently the length p r, or 
-J-D, must be the same in all. Therefore the equation, expressing 
the equilibrium between the momentum of the external force and 
the accumulated momenta of cohesion, will be WL=FDBxJD. 

The product DB, evidently expresses the area of the section of 
fracture, which we may call S, and w^e may express the equili- 
brium thus, WL=FS ID, and 2 L : D=FS : W. 

Now FS is a proper expression of the absolute cohesion of the 
section of fracture, and W is a proper measure of its strength in 
relation to a power applied at n. We may therefore say that 
twice the length of a rectangular beam is to the depth, as the absolute 
cohesion is to the relative strength. 

799. Since the action of equable cohesion is similar to the action 
'of equcd gravity, it follows that whatever is the figure of the sec- 
4ion^ the relative strength will be the same as if the absolute 
<:ohesion of all the fibres were acting at the centre of gravity of 
the section. Let G be the distance between the centre of gravity 
of the section and the axis of fracture, and we shall have 
WL=FSG, and L : G==FS : W. It will be very useful to recol- 
lect this analogy in words: The length of a prismatic beam of any 
shape, is to the height of the centre of gravity above the lorver side, as 
the absolute cohesion is to the strength relative to this length. Because 

^ I ^ . .u r .11, • FBDJD EBD^ 

the relative strength ot a rectangular beam is — — — or -— p- 

L< /& J-i 

it follows that the relative strengths of diflferent beams are propor- 
tional to the absolute cohesion of the particles, to the breadth, and 
to the square of the depth directly, and to the length inversely; 
also in prisms whose sections are similar, the strengths are as the 
cubes of the diameters. 

800. Such are the more general results of the mechanism of this 
transverse strain, in the hypothesis that all the particles are exert- 
ing equal forces in the instant of fracture. But the hypothesis of 
equal cohesion being exerted by all the particles in the instant of 
fracture, is not conformable to nature; for we know that when a 
force is applied laterally against a beam, one side will become 
convex and have its particles on the stretch, while the other, be- 
coming concave, will condense them. The particles on one side 



OF THE RELATIVE STRENGTH OF MATERIALS. 435 

will, thereforej be moved further from each other than those on 
that which is opposite; and it is impossible to say, with precision, 
to what extent the fibres are acted upon; but the probabiHty is 
that the extensions are proportional to the distances from the ful- 
crum or centre of motion. Assuming this to be correct, and ad- 
mitting the law, that in all moderate extensions, the attractive 
forces exerted by the dilated particles are proportional to their 
dilatations, Professor Robison enters upon a further investigation, 
from which he deduces the analogy that *^As thrice the length of a 
beam is to its depth, so is the absolute cohesion to the relative strength." 
We are chiefly indebted for this doctrine to the celebrated Galileo; 
and it was one of the first specimens of the application of mathe- 
matics to the science of nature. He, however, proceeded on the 
supposition that the fulcrum was on the outside of the beam where 
the fracture ends. But Mr. Barlow has since proved that it is 
wholly within the section, and he calls this line the neutral axis. 

801. In the preceding investigation no notice has been taken of 
the action of that force which tends to cause the part op In oi the 
beam to slide down vertically in the direction of the line o p in 
front of the part k o m p that is fixed in the wall; because this 
force is so small in comparison* to the others that exist, that no 
notice need be taken of it in any practical application. 

802. Applying these principles to practice and we find that 
The strength of a beam, or bar of wood, or metal, SfC, in a lateral 

or transverse direction, to resist a force acting laterally, is proportional 
to the area or sectiort of the beam in that place drarvn into the distance 
of its centre of gravity from the place where the force acts, or where the 
fracture zvill end. 

Thus, let A B, Fig. 145, represent a stick of timber or other 
rectangular beam, supported upon props at its two ends, while it 
is pressed upon by the weight W placed over its centre, and 
which may be supposed heavy enough to break it; and let ab c d 
be a cross section taken under such weight. The fracture will, 
under these circumstances, commence at the bottom of the beam, 
and will proceed upwards in a direction nearly coincident with 
that section. The power of a beam so disposed to resist fracture, 
must be proportionate to the number of fibres or contiguous coher- 
ing particles that are contained in the section, and the operation 
would be similar in eflfect to a simple longitudinal force (723), if 
the leverage before described did not operate to produce a change; 
but the reaction of the props under A and B being equal to the 
whole weight supported, and severally acting at the long ends of 
bent levers AW a, BWa, AW6, BWb, &c., produced by supposing 
the beam divided into an infinite number of equal horizontal 
laminae, the tendency to fracture from this leverage will be less- 



436 OP THE RELATIVE STRENGTH OF MATERIALS. 

ened as the shorter arms Wa, W6, &c. are increased, while the 
longer arms remain the same; therefore the strength being in- 
versely as the stress, will be regularly increased as the distance 
of any lamina from W is increased, and the sum of all these forces 
will express the power that is called into action to separate the 
fibres or particles of the beam. The resistance to this power will, 
however, depend upon the sectional area; therefore we must also 
consider the thickness of the beam as shewn in Fig. 146, instead 
of regarding its height only as in Fig. 145. Now the area a e in 
Fig. 146, contains and denotes the sum of all the fibres to be 
broken or torn asunder; and as they are supposed to be all equal 
to one another in absolute strength, that area will denote the 
aggregate or whole strength of all the fibres in the longitudinal 
direction. The fulcri or centres of motion of the levers before 
referred to will all be in the line e e; consequently, each fibre in 
the line a h will resist the fracture by a force proportional to the 
product of its individual strength into its distance a e from the 
centre of motion; consequently, the resistance of all the fibres in 
a h will be expressed hj ahXa e. In like manner the aggregate 
resistance of another course of fibres, parallel to a i as c c, will be 
denoted by c cXc e; and a third as d dhy d dxd e, and all these 
products will express the total strength or resistance of all the 
fibres, or of the beam in that part. But it is demonstrable that the 
sum of all these products is equal to the product of the area aeeb 
into the distance of its centre of gravity from e e; hence the pro- 
position is manifest. 

803. We learn from the above, that the lateral strength of any 
beam or bar, is considerably less than its absolute longitudinal 
strength either against extension or compression; or that it will 
break with a much smaller force when applied laterally; because 
in the one case the fibres must be all separated at once, or in an 
instant; while in the other, they are overcome and separated suc- 
cessively, or one after another in some perceptible portion of time. 
An experimental proof of this is offered in a common walking 
stick, which will support an immense load hanging perpendicularly 
beneath it, or will sustain a great load pressing in the direction of 
its length, provided the stick can be kept from bending; but if 
the bended knee is applied to the centre of such a stick, while the 
two hands draw the ends towards you, it will break with a com- 
paratively small force. Thus originates a principle in carpentry 
which will be insisted on in the next chapter as being of great 
importance to the stability of all constructions, which is never to 
admit a lateral strain in any case where there is the possibility of 
substituting a longitudinal one for it. 

804. We also learn the great advantage that arises from using 



OP THE RELATIVE STRENGTH OF MATERIALS. 437 

timber or metal beams, which oppose considerable depth to the 
direction of the lateral force, notwithstanding they may be thin in 
the opposite direction; and as rectangular pieces of timber or iron, 
such as are generally used in constructing buildings or machinery, 
may in general be considered as homogeneous, their centres of 
gravity will be found in the centre of their dimensions; conse- 
quently the application becomes very easy. Suppose for exam- 
ple, in placing a girder to support a floor, we select a square stick 
of timber measuring 12 inches on each side, its transverse sectional 
area will of course be 144 square inches, and its centre of gravity 
will be in its centre, or 6 inches from either side. Being used in 
a floor, its tendency to bend in consequence of any superposed 
load, will be downwards, and if it breaks, the fracture will termi- 
nate at the upper surface, or 6 inches above the centre of gravity; 
consequently, the area 144 inches, must be multiplied by 6 inches, 
making 864 as a representative number, by which to compare 
the lateral strength of this piece with any other. Being square, 
this piece may be placed with any side upwards, without produc- 
ing any alteration in the elements of calculation. The result will 
therefore be the same for every side, or its strength will not be 
aflfected by placing the one or other side uppermost. 

805. Let us next suppose this girder to be sawed longitudinally 
through its middle, so as to produce two equal pieces of timber 
the sides of which are 6 and 12 inches, or exposing an area each 
of 72 square inches, and placing them as before with the 12 inch 
sides vertically, let us examine what change will be produced. 
As the girder is still 12 inches high, the position of the centre of 
gravity will not be altered, but will still remain 6 inches below 
the upper surface; consequently, the area 72 must be multiplied 
by 6, producing 432, which is exactly half the product obtained 
when the timber had double the breadth. We thus see that while 
the depth remains the same, the strength varies as the thickness, 
and that the same strength may be obtained in a building by 
multiplying small pieces as by using fewer large ones. 

806. Again let us examine the effect of using the same last men- 
tioned timbers measuring 6 by 12 inches, with the 6 inch sides ver- 
tical instead of the 12 inches. The area 72 inches of course re- 
mains unaltered; but the centre of gravity will now be only 3 
inches below the upper surface, so that multiplying 72 by 3 we 
only obtain 216, or half the former strength, notwithstanding the 
quantity of timber remains undiminished. 

If instead of selecting a girder 12 inches square to support the 
floor, one of 14 by 10 inches had been taken, this would only con- 
tain 140 superficial inches in its area, and would therefore be 
cheaper as containing less timber than the 12 by 12 inch piece, 



438 OP THE RELATIVE STRENGTH OP MATERIALS. 

and yet considerably stronger when placed with its largest dimen- 
sion upright, for now the centre of gravity would be 7 inches 
beneath the upper surface, and 140x7=980, so that 140 super- 
ficial inches produces a strength of 980, while 144 inches only 
produces 864. 

807. On this same principle we see why a board can support 
so much more when it is placed with its edge upwards, than when 
placed flatwise like a shelf. Suppose the board 10 inches wide 
and one inch thick, its sectional area will then be 10 superficial 
inches. When placed with its edge upwards, its centre of gravity 
will be 5 inches from the upper edge, and 10x5=50; but when 
placed flatwise, its multiplier will be only J an inch, and 10X-^=5. 
It is therefore 10 times stronger against lateral pressure in the 
first position, to what it is in the second. 

808. For the same reason, a triangular beam is twice as strong 
against lateral pressure when resting on its broad base, as it is 
when resting on its edge, notwithstanding the area is the same in 
both cases. For the transverse section of such a beam must be a 
triangle; and the centre of gravity of a triangle is ^d of its height 
from the base, or §ds from the apex. These distances being as 
2 to 1, so of course if a triangular beam is placed with its base 
downwards, the centre of gravity will be twice as far below 
the top of the beam or place where the fracture will end, as it 
will be if the base is upwards; consequently, the multiplier will 
be twice as large in the one case as in the other, and the strengths 
will be in the same ratio. 

From the above principle several useful corollaries are deriv- 
able. 

809. Corol. Isf. — In square beams the lateral strengths are as the 
cubes of the breadth or depth. 

810. Corol. 2nd. — In general, the lateral strengths of any bars, 
whose sections are similar figures, are as the cubes of the similar 
sides of the section. 

811. Corol. Sd. — In cylindrical beams, the lateral strengths are 
as the cubes of the diameters. 

812. Corol. 4th. — In rectangular beams, the lateral strengths are 
to each other as the breadths and square of the depths, for here 
the area being as the product of the two sides, and the distance of 
the centre of gravity being equal to half the perpendicular side, 
and therefore proportioned to that side; the proposition is that the 
strength varies as the breadth multiplied by the depth, multiplied 
again by the depth, or as the breadth into the square of the depth. 
Hence, as above shown, the same oblong beam, with its narrow 
side upwards, is as much stronger than with its broad side upwards, 
as the depth exceeds the breadth. 



OF THE RELATIVE STRENGTH OF MATERIALS. 439 

813. Corol. 5th. — If a beam be fixed firmly at one end into a 
wall so that it may project horizontally, and its fracture be caused 
by a weight applied at the opposite end, the process will be the 
same; only that the fracture would commence above and terminate 
at the lower side; and the proposition, and all the corollaries, would 
still hold g;ood. 

814. Corol. 6th. — When a cylinder or prism is made hollow, it is 
stronger than when solid with an equal quantity of materials and 
length, in the same proportion as its outer diameter is greater; and 
if the hollow beam is not meant to revolve, and has the hollow, or 
pipe, nearest to that side where the fracture must end, it will be 
still stronger. 

In the foregoing proposition (802) no reference is made to the 
length of the beam, but 

815. In beams of different lengths, resting on two supports ^ like 
Figs. 143, 145, and 146, the strength will vary as the area of the sec- 
tion, into the depth of the centre of gravity, divided by the length into 
the weight. 

Let LI denote the lengths; Ww the weights; Aa the areas of the 
sections; and Gg the depths of the centres of gravity of two pris- 
matic beams resting horizontally on their two ends. 

The stress, or tendency to produce fracture from the weight of 
the beam itself, will be expressed by |^LxW and ^Ixw; for the 
reaction at each support is a force=^ W acting upon ^L at the 
centre of gravity; but the centre of gravity of ^ L is at a distance 
from the prop=-J^ of ^L, or iL; therefore the elfect of the force 
will be equal to ^ Lx^ W=^LxW. 

The tendency to resist fracture is denoted by AxG and aXg, 
Hence the aggregate strength of the timber will be directly as the 
latter, and inversely as the former. That is 

^^ _ AxG . aXg _ AxG \ aXg 
^LxW * ^Ixw " LxW ' Ixw 

816. The lateral strength of prismatic beams of the same materials 
is directly as the areas of their sections, and the distances of their cen- 
tres of gravity; and inversely as their lengths and weights. 

Let AB and CD, Fig. 144, represent two such beams fixed 
horizontally by their ends C and A into a wall. No\n' by the first 
proposition, (802,) the strength of either beam considered as with- 
out, or independent of weight, is as its section drawn into the dis- 
tance of its centre of gravity from the fixed point; viz. as sc, 
where s denotes the transverse section at A or C, and c the dis- 
tance of its centre of gravity above the lowest point of A or C. 
But the effort of their weights W, or w, tending to separate the 
fibres and produce fracture, are by the principles of the lever, as 



440 OF THE RELATIVE STRENGTH OF MATERIALS. 

the weight drawn into the distance of the place where it may be 
supposed to be collected and applied, which is the centre of gravity, 
situated in the middle of the length of the beam; that is, the effort 
of the weight upon the beam is as WxJAB, or wX^CD. 

817. Corol. 1st. — Any extraneous weight or force applied any 
where to the beam, will exercise a similar power to break it as 
its own weight; that is, its effect will be as wxd, or as the weight 
drawn into the length of lever, or distance from A or C, where it 
is applied. 

818. Corol. 2nd. — When the beam is fixed at both ends the same 
property will hold good, with this difference only; that in this case, 
the beam is of the same strength as another of an equal section 
and only half the length, when fixed only at one end. For if the 
longer beam should be bisected, or cut in halves, each half would 
be in the same circumstances with respect to its fixed end, as the 
shorter beam of equal length. 

819. Corol. Sd. — Square prisms and cylinders have their lateral 
strength proportional to the cubes of their depths or diameters 
directly, and to their lengths and weights inversely. 

820. Corol. 4th. — Similar prisms and cylinders have their 
strengths inversely proportional to their like linear dimensions — 
the smaller being comparatively larger in that proportion. For 
their strength increases as the cube of the diameter, or of their 
length; but their stress, from their weight and length of lever, as 
the fourth power of the length. 

821. From the foregoing deductions it follows, that in similar 
bodies of the same texture, the force which tends to break them, 
or make them liable to injury by accidents in the larger bodies, 
increases in a higher proportion, than the force that tends to pre- 
serve them entire, or to secure them against such accidents; their 
disadvantage, or tendency to break by their own weight, increas- 
ing in the same proportion as their length increases; so that 
although a small beam may be firm and secure, yet a larger but 
similar one may be so long as to break by its own weight. This 
is particularly deserving the attention of the Engineer, who may 
frequently have models of machines to execute before he attempts 
them on a large scale; or who may have models presented to him 
for his inspection and approval. He must, in such cases, bear in 
mind that what may appear very firm and successful in a model, 
or small machine, may be weak and infirm, or may even fall to 
pieces by its own weight, when it is executed on large dimensions, 
even according with the scale or proportion of the model. 

822. This same principle places hmits of extension to the pro- 
ductions both of nature and art. Thus, if trees grew much larger 
than we are accustomed to find them, their branches would break 



OF THE RELATIVE STRENGTH OP MATERIALS. 441 

and fall from their own weight: so with floors, roofs, arches, and 
many other artificial constructions. The larger they become, and 
the grosser must be the proportions of the materials used to form 
them, so that they become unpjeasing to the eye, and so enormous- 
ly heavy as to crush and destroy their supporting bearings, by the 
enormity of their own pressure. 

823. If a weight he placed, or a force act, on any part of a horizon- 
tal beam supported at both ends; the stress upon that part will be as the 
rectangle, or product, of its two distances from the supported ends. 

Let AB, Fig. 147, be the beam so supported, and W a weight 
suspended from, or placed upon, the point C; then the stress upon 
the beam AB, at C, by the weight W, is as ACxBC. For by the 
nature of the lever, the effect of the weight W on the lever AC, 
is ACxW; and the effect of this force acting at C, on the lever 
BC, is ACxWxBC=ACxBCxW. And the weight W being 
given, the effect, or stress, is as ACxBC. 

824. Carol. 1st. — The greatest stress is when the weight acts in 
the middle of the beam; for then the rectangle of the two halves 
ACxAC=JABxiAB=JAB2 is the greatest. And from the mid- 
dle point the stress is less and less all the way to the extremities, 
where it is nothing. Hence in practice, where a load has to be 
supported on the middle of a beam, that middle ought to be 
stronger than the two extremities, a part of which may be cut 
away according to a certain rule to be presently explained, (see 
837) without abstracting at all from its strength. 

825. Corol. 2nd. — If instead of the weight being applied to any 
point in the beam, it is diffused equally all over it, the same 
effects will occur; but the stress in this case will only amount to 
half of what it would otherwise be. Hence in all structures, we 
should avoid as much as possible placing loads or strains in the 
middle of beams. 

826. Corol. 3d. — If w be the greatest weight that a beam can 
sustain at its middle point, and it is required to find the place 
where it will support any greater weight W, that point will be 
found by saying as W : zy : : |ABxJAB, or |^AB^ : ACxBC or 
ABx (AB— AC)=ABxA— AC^ 

The foregoing observations apply to beams supported at both 
ends, and we now proceed to the case where the beam is support- 
ed at one end only. 

827. In similar prismatic or cylindrical beams supported at one end 
only, the strength varies inversely, either as the diameter or as the 
length. 

Let ABEF, ab ef Fig. 148, represent the longitudinal sections 
of two prismatic beams fixed horizontally into the wall HK, then 
the power of these beams to resist fracture at the ends EF, ef, 
5Q 



442 OF THE RELATIVE STRENGTH OF MATERIALS. 

where they are inserted into the wall, will be measured in the 
same manner as in the preceding cases, that is, by the area of the 
lateral section into the depth of its cejitre of gravity (802). In this 
case, the fracture will begin at the upper points Yf and end at 
the lower points Ee. The tendency to produce fracture will be 
the weight of the beams acting at the distance of their centres of 
gravity, from the supported ends EF, ef. Hence 

S : 5 :: — — — - : ^ , , or if any weights W zo' are placed at 
JLxW ^/Xtt J ^ r 

the ends of the beams, then (since the effects of these weights to 
produce fracture will be measured by W'xL, andzy'x/) we have 

AxG aXg 

S : 5 : : — = : — r= — ; and if the weights W, w, of the 

L.iVV+W l\w+w ^ - 

beams are very small when compared with the added weights 

W, w', then S : 5 : : r- — -— : ^—~- 

LxW Ixw 

Hence in similar beams S : 5 : : ^p- : — - or — - : — -. 

D a Lt I 

Let Wz«, represent the weights of the parts ABCD, ah c d 
of the beams, (Fig. 148,) then the tendency of those parts to pro- 
duce fracture at Cc, will be measured by ^ACxW, and \acxw\ 
therefore if S^, represent the strength of the beams at C and c, 

AxG aXs 

then S : 5 : : — : ; or if Ww, be very 

ACx-l-W+W acx^w+w' ^ 

small with respect to W and w', then S : 5 : : -r— — -^y^-: ^ . 

* ACxW acXw' 

Hence, if a given weight W, be supported at the end of a 
given beam, whose weight is so small as not to be taken into con- 
sideration, the strength of that beam to support the weight W at 

AxG 
any point C, between A and F, will vary as _— — — ; or since 

W is constant, as — 77^"* 

828. So far, we have throughout considered the beams under 
examination as placed in horizontal positions; but in the construc- 
tion of roofs, and many other cases, beams are made use of in 
positions that incline to the horizon, and in such cases a variation 
in the mode of investigation becomes necessary. Thus, 

When a beam is placed in an angular position with respect to the 
horizofi, its strength to resist a vertical force, is to its strength when 



OF THE RELATIVE STRENGTH OP MATERIALS. 44S 

placed horizontally, as the square of the radius is to the cosine of the 
angle of elevation. 

L^t a b, Fig. 149, represent a sloping beann; draw cf perpen- 
dicular to the horizon afg; then c d will be the vertical section 
of the beam at the point c; and c e perpendicular to a 6 is the 
transverse section, being the same as in the horizontal position. 
Now the strength in both positions, is as the section drawn into 
the distance of its centre of gravity from the point c. But the 
sections being of the same breadth, are as their depths c d, c e; 
and the distances of the centres of gravities are as the same depths; 
therefore the strengths are as cdxcd to ceXce or cd^ : ce^. But by 
the similar triangles c de, afd il k c d : c e :: ad : af, or as radius 
to the cosine of the elevation. Therefore the oblique strength is 
to the transverse strength, as a d^ to af^ or the square of radius to 
the square of the cosine of elevation. 

829. Hence, every beam is weakest against lateral pressure 
when in a horizontal position, and becomes stronger and stronger 
as it revolves into a vertical position, where it reaches its maximum 
strength. 

830. When beams stand obliquely, and sustain weights either at 
their middle points, or in any other similar situations, or equally dif- 
fused over their whole lengths, the strains upon them are directly as the 
weights, and the lengths, and the cosines of elevation. 

For in the inclined plane the weight is to the pressure on the 
plane as a c is to af or as radius to the cosine of elevation; there- 
fore the pressure is as the weight drawn into the cosine of the 
elevation: hence, the stress will be as the length of the beam and 
this force; that is, as the weight X length X cosine of elevation. 

831. Corol. 1st. — When the lengths and weights of beams are 
the same, the stress is as the cosine of elevation. It is therefore 
greatest in horizontal beams. 

832. Corol. 2nd. — In all similar positions, and the weights vary- 
ing as the lengths, or the beams uniform, then the stress varies as 
the squares of the lengths. 

833. Corol. Sd. — Suppose afg to represent a horizontal beam, 
and a db (Fig. 149) a sloping one. When the weights on the two 
beams are equal, the stress upon them will also be equal when 
^ 6 is vertical. For the length into the cosine of elevation is the 
same in both; or a6xcos. a=a^x radius. 

834. Corol. 4th. — But if the weights on the beams vary as their 
lengths, then the stress will also vary in the same ratio. 

835. Corol. 5th. — And universally the stress upon any point of 
an oblique beam, is as the rectangle of the segments of the beam, 
and the weight and cosine of inclination directly, and the length 
inversely. 



444 OF THE RELATIVE STRENGTH OF MATERIALS. 

836. When a beam is intended to sustain any force or pressure act- 
ing laterally upon it, its strength ought to he proportioned to the stress 
upon it. That is to say, the breadth multiplied by the square of the 
depth, or in similar sections, the cube of the diameter in every place 
ouffht to be proportional to the lens^th drawn into the weight or force 
acting upon it. And the same is true of several different pieces of 
similar material compared together. 

It is obvious that every piece of timber or metal, as well as 
every part of the same used in a building or the construction of a 
niachine, ought to have its strength proportioned to the weight, 
force, or pressure it is intended to sustain. Therefore the strength 
ought to be universally or in every part, as the stress upon that 
part. But the strength is as the breadth into the square of the 
depth, and the stress is as the weight or force into the distance it 
acts at. Therefore these must be in a constant ratio to each 
other to produce the desired effect. This general property gives 
. rise to the adoption of different shapes in beams, according to the 
particular circumstances in which they may be placed. An at- 
tention to this property is of less importance in timber work than 
in the metals; because the former material is comparatively light 
and cheap, and it would often cost more in labour to cut a stick 
of timber into its true mathematical form, than the saved timber 
would amount to. But in using metals, the case is different, for 
they are both heavy and expensive; consequently, if we neglect 
the natural laws of diminution, which may be resorted to without 
impairing the strength, we should not only throw much unneces- 
sary and even detrimental burthen into our construction, but use- 
lessly augment its expense. 

Thus, for instance, it has been explained (793) in reference to 
Fig. 144, that the greatest stress upon the beam o I p nism the 
line p, and that the weight w cannot exert so much force to bend 
or break the beam, in any point intermediate between jo and n, 
as it exerts at p. This being the case, it is evident that the beam 
need not be as strong towards its end n, as at op, and yet that it 
will be equally capable of sustaining its load; independent of 
which, the substance that might be cut away near the end In, 
would relieve the part o jo of the useless weight of that portion of 
material, and the beam would, therefore, be rendered effectually 
stronger, as a v/hole, by making it weaker in a part where strength 
is not required. 

837. In like manner, it was lately stated, (824,) that when a 
load is placed upon the middle of a horizontal beam, that middle 
requires to be stronger than the ends, and that although a pris- 
matic or parallel stick of timber is generally used for such pur- 
poses, having equal areas and equal positive strength throughout. 



OP THE RELATIVE STRENGTH OF MATERIALS. 445 

yet a large quantity of the substance of the ends might be cut 
away without impairing its strength. We shall next proceed to 
examine where such cutting away is desirable, and the rules by 
which it may be executed with certainty and advantage, of which 
there are many cases. 

838. 1st. Suppose that the strain arises from a weight to be 
supported at the extreme end of a beam, the other end of which 
is firmly fixed in a wall. This admits of at least three cases de- 
pending upon the form we may be obliged, from circumstances, to 
give to the supporting piece. It may be necessary to have both 
its upper and under surfaces flat or horizontal planes, parallel to 
each other; or, 2ndly, it may be necessary to have the two verti- 
cal sides parallel planes; or, ^dly, the supporter may be circular 
in its transverse sections. 

839. The first case will be met by giving the supporter the 
form of an isosceles wedge as at ABD, Fig. 150, in which the flat 
top and bottom are parallel to the horizon; for if we call the area 
of any section a, the given depth d, and the distance of the centre 
of gravity from the top g^ then a=BDxc? and g^^d .\ aXg= 
^BDxd^, which varies as BD or BC, which also varies as AC. 

AC 

Hence the strength is as — -, that is, it is constant. This form 

only requires half the material that would be necessary for a rec- 
tangular support. 

840. Second case. — When the sides of the beam must be ver- 
tical parallel planes, the depth must vary so that d^ shall be every 
where proportional to I the length. This will be obtained by 
making the depths of the beam the ordinates of a common para- 
bola, of which the extreme end of the beam is the vertex and its 
length the axis. The upper or under side of the support may be 
a plane as efg, in Fig. 150, where the upper side is flat; or both 
the upper and under surfaces may be curved, provided the dis- 
tances between them in every part be as the ordinates of a com- 
mon parabola. In this form one-third of the material is saved, or 
dispensed with, without any diminution of strength. The double 
parabola, or plate, equally curved at its top and bottom edges is 
always resorted to for forming the vibrating beams of steam en- 
gines, when they are made of cast iron. 

841. Third case. — When the support is circular, or the sections 
in all places will form similar figures, whether they be circles, 
squares, or similar polygons; then we must have c?^ or 6^ propor- 
tional to /; or the depths or breadths must be as the ordinates of 
a cubical parabola. This would also be the strongest form for a 
steeple or light-house, exposed to high wind or storms. 

842. If the weight, or load, instead of being applied to the ex- 



446 OF THE RELATIVE STRENGTH OF MATERIALS. 

treme end of the support is uniformly distributed over every part 
of it, as in those brackets called in building Cantilevers, Rnd which 
are used to support balconies, galleries, and heavy cornices, if one 
surface is plane, or right lined, and its two sides are parallel ver- 
tical planes, then the other surface, whether top or bottom, will be 
right lined also, but making an angle with the other surface as 
d b e, Fig. 151. Then b d will always be as o? e and b e, b d two 
right Hues; consequently db e is r wedge, and half the beam may 
be cut away without diminution of strength. Cantilevers are often 
much ornamented by being formed like leaves, &c.; but the orna- 
ments must not cut into the lower line e 6, or the strength will be 
impaired. 

Beams supported at both ends. 

843. When a beam, supported at both ends, is to be of uniform 
depth, from one end to the other, and is intended to sustain a load 
in any fixed point near its middle, its horizontal section should be 
two isosceles triangles, joined base to base, as in Fig. 152, the junc- 
tion of the bases c being the point at which the load is to be de- 
posited (889). 

As this form would be inconvenient in practice, on account of 
the very narrow bearings the beam would have at its ends, upon 
the supporting walls, it is customary to extend the breadth of the 
ends, as shown by dotted lines at /*, instead of letting them termi- 
nate in sharp angular points. The plan of the beam would then 
be such as is shown by the dotted lines drawn from/. If the beam 
is formed of cast iron, then the form dotted in at the end g may 
be given to it. Or the beam may be formed of a flat plate formed 
in plan like the end g, and the double isosceles wedge may be 
cast on its under side, so as to form a feather (624) to it, causing 
the whole beam to assume a form like Fig. 153, when viewed from 
one side. 

844. As a general rule to be attended to in the use of beams in build- 
ings, their ends ought never to rest immediately upon the bricks 
or stones that support them, particularly when the load the beam 
may have to carry is very considerable; because the breadth of 
a beam is never very great, and if it rests immediately upon the 
wall, the whole load will be transferred to the single stone, or few 
bricks that may be directly under the ends of the beam, and they 
may thereby be crushed. A piece of timber, or a plate of cast 
iron, called a template, should therefore be constantly placed in a 
transverse direction, or at right angles, to the axis of the beam, 
upon the wall under each end of the beam, for its ends to rest 
upon, as shown at hh. Figs. 152 and 153. The length and thick- 



OF THE RELATIVE STRENGTH OF MATERIALS. 447 

ness of the template must be regulated by the load it has to bear, 
and the solidity of the materials under it; and its use is to distri- 
bute the load of the beam over a considerable quantity of the wall, 
instead of permitting it to operate on a confined spot. Wooden 
templates are generally used for wooden beams, and open sand 
cast iron plates for cast iron beams. Their edges may be flush 
with the inside of the wall, but they must not be so wide as to ap- 
pear on its outside. Templates should be bedded in mortar, and 
where iron is the material used, if the under bearing of the beam 
and the top surface of the template do not coincide accurately, 
the beam should be prevented from rocking or moving by driving 
small iron wedges between the two, and then running melted lead 
between them; the iron having been previously heated by a char- 
coal fire built upon it, and when cold, the lead should be caulked 
in by a caulking chisel. 

845. A beam with plane and parallel vertical sides, that is in- 
tended to support a permanent load upon any one point, should be 
formed of two parabolas, united at cd, where the pressure occurs, 
as in Fig. 154. The top or bottom surface may be right lined, or 
both may be curved, provided the conditions of proportion, before 
described, (840,) are preserved. The extended ends, dotted in, in 
the figure, are to give the beam a proper bearing on the walls. 

846. The same effect of strength will be very nearly produced 
by right lines only, as in Fig. 155, in which two right lined wedges 
are used, being united at c, where the fixed load is placed. In 
this case, the depth at the ends must be equal to half the greatest 
depth c, where the load is placed. 

847. Fig. 156 shows how a very large beam of this description 
may be formed of cast iron, with the least consumption of metal. 
It consists of two plates at right angles to each other, but cast in 
one mass, as shown by Fig. A, (being a section of the beam,) by 
which stiffness is produced. The vertical plate has the necessary 
contour to insure strength when the load is placed at c, but a con- 
siderable quantity of metal is saved by the holes or perforations 
eee, which are left through it. 

848. When the load is not confined to a particular point in a 
beam, but is equally distributed over it without being subject to 
change, and the two ends are firmly fixed in opposite walls, the 
middle part of the beam may be weaker than its ends; because 
in this case such a beam may be assimilated to two opposite 
wedges, like Fig. 151, meeting at their points, 6, although in 
practice some considerable depth is always given to the middle or 
junction of what otherwise would be sharp, angular edges. 

849. When the load is equally distributed, but is not fixed in 
its position, but is liable to change from one part to another, as in 



448 OF THE RELATIVE STRENGTH OP MATERIALS. 

rail-road plates, or girders for supporting the floors of ware- 
houses, which may sometimes be laden in one part and sometimes 
in another, and where the ends of the beams cannot be firmly 
and immovably fixed, the elliptic, or semi-elliptic section is the 
best, being the form shown by Fig. 157; because when the beam 
is bounded by two parallel planes, perpendicular to the horizon, 
de^ will, in all positions, be as the rectangle a d into the rectangle 
of d b, and the curve a e b will be an ellipsis. If the figure was 
solid, as shown by the dotted line, so as to cause all its transverse 
sections to be similar figures, then d e^ would bear the same pro- 
portion to the two rectangles, and the condition of strength would 
be still greater. 

850. After the foregoing observations, the use of transverse 
plates or surfaces at right angles to each other, called feathers in 
foundry work, as before described, (6.24, 626,) will be sufficiently 
obvious, as well as the principles upon which their superior 
strength depends. Fig. 133, PI. IV., is a section of such a plate 
or beam in which the upper surface is flat and smooth for receiv- 
ing joists or building a wall upon. But if we desire to give still 
greater strength to such abeam, its transverse section should pre- 
sent a regular cross, as shown by Fig. 158. This form is con- 
stantly adopted for what is called the connecting rod of large 
steam engines; being the piece that connects one end of the 
vibrating beam with the crank of the fly wheel, when such rod is 
made of cast iron, and it also swells or enlarges in the middle of 
its length where it would be subject to bend by vibration. A 
similar form is likewise frequently adopted for cast iron pillars or 
columns for supporting great weights. Fig. 159 is the transverse 
section of another form of cast iron beam which is very much 
used for beams, girders, and columns, where great strength is re- 
quired, particularly if the strain is likely to come from one side,, 
as next B, for instance. This beam consists of the union of three 
flat plates, which are cast in one piece. It has greater strength 
in the direction of the width of the two flat plates than of the one, 
but it may, nevertheless, be trusted in the position shown in the 
figure for a girder in most instances, and it is convenient, and 
saves room when so used, because instead of the joists running 
over the girder and taking nearly double its height, they may be 
morticed or cut out to fit into the hollows on each side of the 
beam, as seen at B, which shows, by dotted lines, the end of a 
timber joist so fitted into one of the longitundinal cavities on the 
side of the iron beam. The cylindrical or slightly tapering form 
is, however, decidedly the handsomest for a column or support, 
and when made of cast iron possesses advantages from being tubu- 
lar or hollow, which have been before explained (623). This 



OP THE RELATIVE STRENGTH OF MATERIALS. 449 

form is likewise advantageous for the journals or revolving shafts 
of mills, because more stiffness and strength is obtained out of the 
same quantity of material than if they were made solid (784). 

85 1 . The lateral strengths of two cylinders of the same material, and 
of equal length and weight, the one heijig hollow, while the other is solid, 
are to each other as the diameters of their sections. 

Let ABG, ab gf Fig. 160, represent the sections of two cylin- 
ders of equal length and weight; AGB being hollow, and a g b 
solid. By the conditions, the area of the ring D must be equal to 
the area of the whole circular section a g b. But the strengths of 
cylinders are as their areas multiplied into the distances of their 
centres of gravity from the points of pressure. G and g are the 
common centres of gravity of both the cylinders, and calling A 
and a the two points of pressure, their relative strength will be 
as a g : AG, or as their radii, and consequently as their diameters. 

852. The strongest form, therefore, in which any given quanti- 
ty of matter can be disposed, is that of a hollow cylinder; and in 
principle, it would seem as if this disposition could be carried to 
a great extent by augmenting the diameter of AB, and that of its 
contained tube. But in this way the annulus might become so 
thin as to be incapable of supporting even its own weight; and 
Tredgold has demonstrated that the maximum of strength is ob- 
tained in cast iron when the thickness of the annulus or ring 
amounts to one-fifth of the external diameter of the cylinder. By 
a property of concentric circles, a chord, c d, drawn across the 
exterior circle will be the diameter of a circle that shall be equal 
in area to the annulus exterior to it; therefore, in the figure c d^a 
b, and by this law it becomes easy to put the same quantity of 
metal in an annular form as would make a solid cylinder of equal 
weight. 

853. Nature adopts this principle in a great variety of cases. 
Thus obtaining lightness and strength at the same time. All the 
principal bones of the animal frame are hollow or tubular. The 
feathers of birds, the straws of wheat and several other grains — 
the stalks of reeds and many plants. Indeed, all trees partake of 
this formation, their first shoots being frequently hollow and filled 
with pith, and as the tree grows and expands, it becomes a series 
of tubes superposed on each other, the hollow of each tube being 
filled up by the previous growth. Still this very construction adds 
strength to the trunk of a tree as well as its branches, and in- 
structs us how to cut up a stick of timber so as to obtain scant- 
lings of varying strength suited to different purposes. Thus let 
Fig. 101 represent the cross section of a round tree consisting of 
concentric annual laminae of wood. The largest piece of timber 
that can be cut out of such a tree will be a die square stick as 

57 



450 OP THE RELATIVE STRENGTH OP MATERIALS. 

shown by the lines a h c d, and this will also be the strongest 
piece, provided it is required to resist strains which vary and act 
towards the centre of the beam; because now the centre of the 
tree is in the centre of the stick, and it will consist almost wholly 
of concentric tubes of wood. Such a piece of timber would be 
better suited than any other (except an entire round tree,) for 
forming an upright post or pillar to bear a vertical load; because 
it will have no greater tendency to bend to one side more than to 
another. A pressure towards the centre of a beam laid horizon- 
tally is a thing that never occurs, and such beams are generally 
laid to support loads pressing downwards. For this purpose the 
scantling ought to be cut in such way that the laminae may coin- 
cide as nearly as possible with the direction of the pressure, and 
this will be the case, if we cut out a piece like efg A, in which as 
many parallel laminae as possible are preserved in a vertical po- 
sition. For the same reason the scantling ig m n (although equal 
in area to the last,) would be the worst that could be selected, 
provided i g or m n was made its top; for now the laminae are all 
nearly horizontal in their width; but if ^ n or m i were made the 
top and bottom, the laminae would become vertical, as in the 
last case, and the greatest strength would be obtained. 

854. The reason for thus attending to the position of the 
laminae in pieces of timber, is that the wood has a natural ten- 
dency to split or divide between them. Each laminae may, there- 
fore, be considered as in the nature of a thin separate board; or a 
stick of timber may be regarded as so many thin boards laid close 
together. We have before seen that a board placed with its edge 
uppermost is capable of supporting a much greater load than 
when its flat side is uppermost (807). The scantling e/^ A, Fig. 
161, may therefore be considered as composed of a number of thin 
boards with their edges uppermost, while i g m n is made up of 
boards laid flatwise, and therefore less prepared to resist pressure 
from above or below. 

855. In obtaining the comparative strength of beams by the 
processes above described, i. e. taking their sectional area, and mul- 
tiplying it into the distance of the centre of gravity from the point 
of pressure, it may appear that no difference should occur in the 
result, whether that area was made up of one solid beam of tim- 
ber or metal, or of a great number of thin boards, plates, or 
laminae piled one upon another until the same depth and width 
was accomplished, since the area and material would be the same 
in both cases. The result would, however, be different; for one 
element in the strength of beams is their rigidity or stiflfness, 
occasioned by the natural cohesion of the particles which prevents 
one set of particles from slipping or sliding oVer another, so that 



OP THE RELATIVE STRENGTH OF MATERIALS. 451 

no very considerable change of form can occur without fracture 
taking place. But when thin plates or laminae are piled one 
above another to produce depth, the action of cohesion will be 
much diminished, and the plates will slide over each other with- 
out difficulty. The bottom plate instead of cohering to the one 
next above it, and thus lending its assistance to produce strength 
and stiffness, may even sink beneath it, and thus withdraw all its 
support: and in like manner the next, and the next above it, and 
so on, may follow, though to a diminished extent. Therefore 
two or more beams placed one above the other in parallel posi- 
tions, can never exert the same effect in supporting a load, as one 
solid piece equal to their conjoined area will do, unless some effec- 
tual method is resorted to for so uniting the pieces that they can- 
not possibly slide over each other. This, on a small scale, may 
be effected by gluing the two pieces together, but the mechanical 
process that is used for this purpose in large work is called jcg-- 
g ling, and is usually performed by making the two. surfaces of 
the pieces that are to be joined so smooth and level that they 
may come into close contact with each other. F and G, Fig. 162, 
show two pieces of timber to be so joined in order to give them 
power to sustain a heavy weight W without swagging. The 
pieces during their preparation are laid on perfectly level tem- 
porary bearings, and being fitted together, a set of transverse 
notches n n n, &-C., are cut in such manner that they project a 
sufficient distance (according to the size of the pieces,) into the 
under side of the upper and top of the lower piece. These notches 
proceed quite across the beams, and the upper and lower corres- 
ponding notches must coincide very accurately with each other. 
That done the two beams are strongly screwed together by iron 
screw bolts b b b, when keys or rectangular blocks of oak, or any 
hard wood are fitted into the holes n n n, and driven forcibly into 
them. If the work is well executed, one piece of timber cannot 
now bend without the other, nor can they slide over each other, 
consequently the same stability and stiffness will be obtained as 
if the whole was one solid piece of timber. 

856. The masts of large ships are of such large diameter that 
no single piece of timber can be obtained big enough to form 
them; and as such masts require great strengjth and stiffness, the 
pieces of timber which compose them are always joggled together. 
The shipwright's joggle is, however, more complicated and diffi- 
cult to execute, and at the same time more wasteful of timber 
than that just described. It is at the same time more durable, 
as it has no detached pieces about it, which would become loose 
by the bending and play of the mast. In this kind of joggling 
the two sides of the timbers that come into contact, are scarfed^ 



452 OP THE RELATIVE STRENGTH OF MATERIALS. 

or let into each other by certain corresponding elevations and 
depressions, cut out of the solid wood, as shewn at Fig. 163. 
The two pieces of timber being thus let into each other, the 
two sides on which the joints show are planed snnooth, and two 
thinner pieces, equal in breadth to the two that have been so 
joined, are again joggled by a nearly similar process upon these 
sides, when the whole are rounded into a cylindrical form, and 
kept together by iron hoops applied round their outsides. By 
joggling, any number of timbers may be thus united, so as to pos- 
sess the stiffness of one piece, and this process is frequently used 
with advantage in the formation of large timber arches, roofs, and 
all constructions where single trees cannot be found to yield tim- 
ber of magnitude sufficient for the intended purpose. 

857. Although a die square stick of timber holds the greatest 
quantity by measurement that can be obtained out of a round 
tree, yet it is advantageous to obtain pieces of the greatest pos- 
sible strength for building purposes, and the stick that is exactly 
square does not fulfil these conditions, because the product of its 
breadth by the square of its depth is not the greatest possible. 
This relation of dimensions will, however, be obtained by draw- 
ing a diameter across the section of the tree as at a d, Fig. 164, 
and dividing it into three equal portions at b and c, upon which 
perpendiculars to the diameter must be raised and prolonged 
until they cut the circumference. Joining the points where the 
circumference is cut by the perpendiculars to the ends a d of the 
diameter by right lines, the rectangle a fde will be produced, 
and this will give the boundary lines of the strongest beam that 
can be cut out of such tree. 

858. It will be perceived that all the foregoing rules point out 
the comparative, and not the actual strength of the beams they 
refer to. They teach us how to compare the strength of one 
beam with that of another, but they do not show us how to com- 
pute the actual weight which any given beam can bear. To ac- 
complish this last problem, data derived from experiment must be 
had recourse to; and hence the use of those investigations and 
tables of strength that were detailed in the second section of the 
present chapter relating to the absolute strength of materials. 
By such tables, the actual or absolute strength of bars, either 
against compression or extension may be pretty nearly ascertain- 
ed, and having determined the power of a bar, it may be con- 
verted into the area of a beam, or large mass, by multiplication, 
with sufficient accuracy for most practical purposes, because a 
large allowance must constantly be made for the strength of ma- 
terials in u?e. Then by the rules before given, (798, 9 and 800,) 
the value of absolute strength can be converted into that of relai- 



OP THE RELATIVE STRENGTH OP MATERIALS. 453 

tive or lateral strength: because the length and other dimen- 
sions of any beam we are about to use, are known quantities; and 
as thrice the length of a beam is to its depth, as its absolute cohe- 
sion (obtained as above,) is to its relative strength, the question is 
readily solved; and all that is then necessary to add is the weight 
of the beam, in order to ascertain what addition it makes, or 
what proportion it bears to the load to be sustained, and this 
weight may be obtained by actual weighing, or by calculation, 
assisted by the table of specific gravities annexed to the end of 
the present chapter. 

859. Independent of the above mode of proceeding, experi- 
ments may be tried on a small scale upon the materials we are 
about to use, and these will either furnish the necessary data in 
themselves, or may be used in proof or corroboration of the calcu- 
lations made as above. Thus, for example, taking a prismatic 
piece of oak, 1 foot long and 1 inch square, it will weigh J a 
pound; and supporting it at its two ends, it will be found capable 
of bearing a weight of 600lbs.: while a bar of iron, of similar 
dimensions, will sustain 2,190/65., and weighs about 3/6^. 

To determine, from such data, what load a 4 inch square piece 
of oak, 6 feet long, could sustain at its middle point? 

Let S=the strength of the beam required; and 5=the strength 
of the trial piece, 1 foot long and 1 inch square, equal 600/6.?. 

W the weight of the larger beam; and w that of the smaller= 
i/6. Let L=6, /=1, D=4, d=l. Weight required=W', the 
given weight {G00lbs.)=w'. 

Then the weight of the beams not being taken into account, 

s • •• ^' . ^' .. 43 ^ P 

' ^ * * LxW * Ix^' * ' QXw' ' 1X600* 

But the strength at the moment of fracture=0 in both cases, 

i. e. S=5 .*. r^,'^ ; whence W'=6400 pounds. 

6XW' 1X600 ^ 

860. If the weight of the beams be taken into account, then 

1)3 ^3 43 p 

S : s 



Lx|WH-W' Ix^w+w 6.24*+W' l.J+600 

64 1 

Hence — — = ^7^77^; and W'=63784 pounds. Ans. 
6.24+W' 600f ' ^ 

The above example is from Professor Olmsted's Introduction to 
Natural Philosophy, 3d edition, 1838, where several other appli- 
cations of the same kind will be found under the head of Strength 
of Materials. In the older writers on this subject, various and 

*ForW :^6•::LxD2:Zx(/^.•.W :^ ::6xl6 : 1 ::96: 1,.-. W=48. 



454 



OF THE RELATIVE STRENGTH OF MATERIALS. 



copious information is given as the absolute strength of materials, 
although practical facts, respecting lateral pressure, are but 
scantily detailed. This most important element, in all constructions, 
therefore had to be worked out by individual calculation and ex- 
periment. This deficiency has, however, been most amply supplied 
by the more recent and highly valuable publications of Tredgold 
and Barlow. Tredgold, in his Practical Essay on the Strength of 
Cast Iron and other Metals, before referred to, gives 15 pages of 
tables by which the strength of cast iron, of all forms and sizes, may 
be determined by very simple formulae, as well as their deflection 
under certain loads; and in his Treatise on Carpentry, a nearly 
similar tabular arrangement is adopted, not only as applying to 
timber, but many other materials of the builder, so that the 
labour of the Engineer and Architect, in making the necessary 
calculations, is not only much abridged, but his work has the ad- 
vantage of being founded upon the most solid principles that 
mathematics can give to a practical act, almost wholly dependant 
upon its principles. Professor Barlow, of Woolwich, promises a 
new edition of his work on the Strength of Timber, which, no 
doubt, will be replete with authentic and valuable information. 

861. Table or the Specific Gravities 



Of such things as are most frequently used by the Engineer, 
Architect, or Builder, by means of whith the weights of masses of 
such articles may be calculated. Pure water is the standard of 
specific gravities, and is called 1. By adding three ciphers it 
becomes 1,000, and since a cubic foot of water, at 40° Fah., weighs 
1000 ounces avoirdupois, or 62^lbs., so striking out the decimal 
point from the specific gravity of any substance, causes the entire 
number to represent the number of ounces contained in a cubic 
foot of that substance, and from this datum the weight of any mass 
may be readily found. The numbers are chiefly extracted from 
Dr. Foung's Natural Philosophy, Vol. II. p. 503. 



Metals. 

Antimony, regulus of, - - 6.624 

Bismuth, do. - - 9.823 

Brass, best yellow, - - 8.370 

Gun metal, (8 cop., 1 tin,) 8.153 

Pot metal, - - - 7.824 

Copper, cast^ .... 7.788 

rolled, - - - 8.750 

Gold, cast, - - . - 19.258 

hammered, - - - 19.362 

Iron, cast, _ - . . 7.207 

malleable in bars. - 7.788 

Lead, cast, - - - - 11.352 

rolled, - - - 11.725 



Mercury, frozen solid, - - 15.632 

at 32«Fah., - - 13.619 

at 60'=' „ - - 13.580 

at 212° „ - - 13.375 

Nickel, cast, - - - - 7.807 

Platina, crude in grains, - 15.602 

in metallic state, - 20.337 

hammered or rolled, 22.069 

Silver, cast pure, - - - 10.474 

hammeredj - - 10.511 

Steel, soft, - - - - 7.833 

hard, . - - - 7.840 

Tin, cast, - - * - - 7.291 

Zinc, cast, (in usual state,) - 6.862 



ON CONSTRUCTION, OR THE PROCESSES OF BUILDING. 455 



Zinc, pure, in rolled sheets, - 

Woods. 

Alder, 

Ash, 

Beech, 

Box wood, (hard Dutch,) 

Cedar, (American.) 

Cherry tree, - - - - 

Cork, 

Cypress, - - - 

Ebony, 

Elm, - - - - - 
Fir, or Pine, fyellow,) - 
(white,) - 
Lignum vitse, _ . - 
Lime tree, _ . - - 
Mahogany, Spanish, 

Honduras, - 

Maple, 

Oak, (English, heart of,) 

good dry, - . - 

Poplar, 

Walnut, . - - . 

Willow, - . . . 

Yew, . - - - - 



Stones, Earths, &c. 

Alabaster, - - - - 
Bath building stone, 
Borax, - - - 
Brick, (best, hard burnt,) 



7.191 



0.800 
0.845 
0.852 
1.328 
0.561 
0.715 
0.250 
0.644 
1.330 
0.544 
0.557 
0.469 
1.333 
0.604 
0.863 
0.560 
0.750 
1.170 
0.932 
0.833 
0.671 
0.585 
0,800 



2.699 
2.200 
1.714 
2.000 



Brick, general average. 
Chalk, British block. 

Do. soft, 
Coal, Cannel and New Castle, 
Inland and British, 
Anthracite, Pennsylvania, 
Flint stones, - - - - 
Granite, Aberdeen blue, 

Cornish, - - - 
most compact spec, 
Grindstones, - - - - 
Gypsum, common opaque, 
best transparent. 
Limestones, vary from - 

to - 
Lime, (quick.) _ - - 
Marble, common slaty, - 
Kilkenny black, 
Brocatella, 
general average, 
Mill stone, - - - - 



Portland building stone, from 



Purbeck stone, 
Porphyrj'', average, 
Serpentine, do. 
Slate, (for roofs,) - 
Sand stones, from - 
to 



Linseed oil, - - - 
Essential oil of turpentine, 
Rectified alcohol, - 



to 



1.845 
2.684 
2.315 
1.269 
1.240 
1.300 
2.582 
2.625 
2.662 
2.761 
2.143 
2.168 
2.274 
2.710 
3.182 
0.843 
2.707 
2.695 
2.650 
2.720 
2.484 
2.113 
2.570 
2.601 
2.750 
2.600 
2.672 
2.000 
2.700 



0.940 

0.870 
0.829 



CHAPTER X. 



ON CONSTRUCTION, OR THE PROCESSES OP BUILDING. 



862. Under this head will be included all such rules and prin- 
ciples of practice as experience has dictated for using the several 
materials that have been described, so as to produce the greatest 
stability and duration in the work, with symmetry and beauty of 
appearance. And as all large constructions are necessarily ex- 
pensive, so the most economical modes of building will at the 
same time be pointed out, or the principles by which the greatest 



456 OP STONE-WORK OR MASONRY. 

strength can be procured out of the smallest quantity of material, 
a problem in which the scientific Engineer will have constant 
exercise for his skill and judgment. 

The operations to be carried on with different materials are 
themselves so different as to demand separate explanations, there- 
fore this chapter will be divided into four sections, treating re- 
spectively of stone-work, brick-work, wood-work, or carpentry 
and joinery; metal-work, and such other matters as could not be 
included with propriety under any of the above mentioned heads, 
and in pursuance of the observation that closed the chapter on 
mensuration, (210,) each section will conclude with the methods 
of measuring and computing the value of the work it describes. 
This arrangement has been adopted for the reason then stated, 
that such mensuration cannot be conducted without using many 
technicalities peculiar to each variety of work which, not having 
been described in the early part of the treatise, would have been 
unintelligible. 

Section I. — Of Stone-work or Masonry, 

863. Building with stone is conducted in several manners, but 
they are all comprehended under the general name o{ masonry, a 
term that in England is appropriated solely to stone-work, as the 
wood mason is to the worker in stone. U, therefore, any thing is 
said to be supported on a mass of masonry, it is generally under- 
stood that such mass consists of stone only. In France the term is 
more general, for they have no other mode of expressing a 
worker in bricks, or bricklayer, than by the compound magon de 
hrique, or magon de pierre, and in this country it is still more gene- 
ral, since we have stone-masons, brick-masons, and marble-masons. 
The latter being that superior class of artists called statuaries in 
Europe, or those who carve and form statues, busts, capitals for 
columns, tombs, monuments, or other highly finished ornamental 
work, but are seldom employed in the mere building or construc- 
tion of edifices. The worker in stone in England is always con- 
sidered as a higher grade of artificer than him who works in 
brick, and therefore called a bricklayer, and on this account he 
would feel his dignity lowered by having his art confounded with 
that of the bricklayer, by calling the latter a brick-mason. 

8G4. The ruins of antiquity still remaining, show to what per- 
fection the art of masonry was carried in the early ages; and 
from the difficulty, accuracy, and skill that is necessary in mak- 
ing perfect constructions in stone-work, those who excelled in it 
were much encouraged, and received many privileges and immu- 
nities not enjoyed by others. Dr. Henry, in his history of Britain, 



OF STONE-WORK OK MASONRY. 457 

attributes the origin of Freemasonry to the difficulty of procur- 
ing a sufficient number of competent workmen to build the mul- 
titude of churches, monasteries, crosses, and other religious edifices 
which the superstition of the early ages prompted the people to 
raise. Hence the masons were greatly favoured by the Popes, 
and many indulgences were granted them in order to augment 
their numbers. In times like these, it may be supposed that 
such encouragement from the supreme pastors of the church must 
have been productive of the most beneficial effects to the frater- 
nity, and hence the increase of the society may be naturally de- 
duced. He even goes further in tracing the origin of this institu- 
tion, stating that some Italian and Greek refugees, and a number 
of French, Germans, and Flemings, joined themselves into a frater- 
nity of architects and builders, procuring papal bulls for their en- 
couragement and protection. They styled themselves Freema- 
sons on account of their enjoying the privilege of working in all 
parts of the country, and they ranged from one nation to another, 
as they found churches to be built. Their government was regu- 
lar, and when they engaged to execute any buildina;, they made 
a camp of huts near it. A surveyor governed in chief, and every 
tenth man was made a warden, and was the foreman or superin- 
tendent of each nine. Freemasons date the origin of their in- 
stitution much earlier, and believe that it commenced with the 
building of Solomon's temple. These observations are, however, 
merely introduced to show the importance of good builders in 
stone in early periods, and how that which was once a working 
society or fraternity of great public importance, has dwindled 
down into a mere social meeting of friends, in which moral pre- 
cepts, metaphorically derived from the arts of building, are incul- 
cated and taught. 

865. The mason conducts all the operations of stone-work after 
the stone is delivered from the quarry, until it appears in the 
finished building, and in small jobs is likewise the merchant, or 
supplier of the stone used in his own work. In lar^e concerns it 
is customary for the Engineer or architect to make his contract 
with the proprietor of some stone quarry, and to order blocks of 
such dimensions and forms as he may require, and these are de- 
livered to the place where they are to be used. The quarryman 
gets out such blocks as are ordered, and dresses them up to some- 
thing near their intended shape, so as to reduce the weight, and 
consequent cost of transportation, as much as possible; and journe}'^- 
men masons are hired who convert them to their ultimate shape, 
and finish them by working as close as possible to the place 
where they are to be used. The Engineer having completed his 
drawings for the intended erection, ascertains bv his scale and 
58 



458 OF STONE-WORK OR MASONRY. 

compasses, what forms of stone will be required, with the magni- 
tude and number of each kind; and he then delivers a correspond- 
ing particular or schedule to the quarry, in which the stones are 
distinguished by numbers, all those stones that are similar in size 
and shape having the same number. This saves much waste of 
time, as well as material, in the execution, because instead of 
having to hunt over a whole field of stone for a piece that would 
fit a particular place, the blocks of stone are identified at once by 
corresponding numbers that are painted upon them at the quarry, 
and each piece that is delivered has its assigned place in the work. 
Great care should also be bestowed upon the distribution of stone 
when it is received, in order to make it convenient of access when 
wanted. The numbering should begin with those stones that are 
to be used first, or in the foundation, and proceed regularly to the 
top of the work; and as the quarryman has the whole list, and 
cannot with certainty know the exact size of the stone he may 
get up, and must get them out of his way, he cannot, of course, 
^ send off the stones according to rotation of numbers, but sends 
away all stones indiscriminately that accord with the sizes in his 
list. It may therefore happen that he despatches a parcel of Nos. 
1, 30, 50, and so on, at the same time. On receiving them they 
therefore require sorting, the low numbers should be laid close to 
the work, No. 2 behind them, and the high numbers in a more 
distant part. Then as all the Nos. 1 are to be used first, they 
will be placed in the work and be out of the way before No. 2 
need be moved. While if No. 1 had been put beyond No. 30, there 
would probably be no means of getting a No. 1 into its place, ex- 
cept by raising and moving it over a number of stones in front of 
it, and stone is too heavy and fragile a material to admit of such 
treatment. For similar reasons alleys or lanes wide enough for a 
truck and horses to pass, ought to be left between the rows of 
stones for the purpose of fetching any of them from their places. 

866. No rule can be given for the size of stones to be used in a 
building, because that must depend alone on local circumstances, 
such as the nature of the stone and facility of obtaining it, and the 
appearance the erection is to have. As a general principle, 
large blocks of stone are preferable to small ones, because the 
strength of stone erections depends more upon the weight and 
goodness of the stone, and the close fitting of its joints than upon 
the adhesion and strength of the mortar. It is therefore advan- 
tageous to use large and heavy stones, and as few mortar joints as 
possible. Still no stone should be so large as to render it incon- 
veniently heavy, or difficulty may occur in working it, moving 
and raising it into its proper place, and finally in adjusting it into 
its final position or bed, particularly if it is to occupy an elevated 



OF STONE-WORK OR MASONRY. 459 

position. The ancients frequently used nnuch larger masses of 
stone than are used in modern constructions, and some of these 
are still existing in the remains of their edifices, which excite sur- 
prise as to how they could have been placed, as the task would 
impose great difficulty upon modern workmen with all their ad- 
vantages and improvements of machinery. 

867. Masonry, or stone-work, is divided into several varieties, 
depending on the quality of the stone, and the manner in which it 
is worked or used. To explain this it is, however, necessary to 
define some of the terms that are made use of in building a wall. 
The bottom of every wall, or erection, whether of stone or brick, 
is called its foundation, and this should, in all cases, be level and 
right lined, not only to give the work a better appearance, but to 
insure equality of pressure, and to avoid any tendency the mate- 
rials would have to slide out of their positions, if they were laid on 
an inclined or sloping bottom. The work always proceeds by 
horizontal layers, or rows of material, which are called courses, 
and these during their formation ought to be constantly examined 
by the bricklayer's level (300), to insure keeping them truly horizon- 
tal. The interval between one course and another, is called a 
horizontal joint or bed, while those that occur laterally between 
one stone and another, are called vertical joints. The outside of 
every wall is called its face, while the inside, or interior, is its back, 
on which account filling up the inside of a wall is frequently called 
backing it up. As the materials of which all walls are built, are 
more tenacious and strong than the mortar ©r cement used to 
unite them, particularly in its recent state, so great care should 
be used in depositing the stones, to so place them in the work as 
to break joint, as it is called, but which means that one vertical 
joint shall not come over another, in two or more successive 
courses; because such a disposition of the blocks of stone not only 
produces a bad appearance in the work, but renders it less strong, 
and may even permit one block to separate laterally from an- 
other. Such a proper disposition of the pieces is called producing 
bond, a term that is derived from one stone bearing upon and hold- 
ing the adjacent stones by its weight and consequent friction, as 
well as by the tenacity of the mortar, thereby binding, or holding, 
the work together. When a wall is spoken of it is always under- 
stood that the parts that compose it, are held together, or united, 
by some mortar or cement placed between the joints, unless a dry 
wall is referred to, and that means any wall built without mortar 
or other soft or cementing material between the joints, when the 
work is said to be laid dry. 

868. The varieties of masonry, above referred to, are called 
rubble stone-work; solid 7vr ought masonry; and ashlar-work. Rub- 



460 OP STONE-WORK OR MASONRY. 

ble stone is the coarsest, cheapest, and worst kind of nnasonry 
that is executed, for it consists of stones of the greatest irregularity 
of shape and size, placed one upon the other, without any regard 
to the closeness of the joints or beauty of appearance; but still the 
stones are so picked out, as to produce the effect of a general flat 
surface on the outer face of the wall, and sometimes on both its faces 
or surfaces. It is divided into three classes, called dry rough stone 
walling or rubble-work; rough rubble-work in mortar; and rubble 
stone-work in courses. The two first classes explain themselves, 
the one being nothing more than rough stones, which ought to be 
large, flat, and not very thick, piled one upon another in such 
manner as to produce as flat a face, or vertical surface, as possible; 
and in executing this work care should be taken to break joint as 
much as possible, and occasionally to introduce thorough stones, or 
stones that run from face to face of the wall, in order to bind or 
tye the two external surfaces together, so as to prevent the wall 
splitting or dividing longitudinally. In executing this work, the 
outside faces of the wall are always' first attended to, and such 
stones are selected for the purpose as will produce the best and 
smoothest surfaces, which are regulated in their straight forward 
direction by a line or cord stretched in the direction in which the 
wall is to be built, while the vertical position is preserved by the 
occasional application of a plumb rule. The outside of a course 
being finished, the inside of the wall is backed by filling in all the 
interstices between one stone and another with fragments of the 
same material, driven into their places by a hammer or stone axe, 
which is the only tool required for this kind of work, with the 
exception of the line and plumb rule. 

869. The second variety, or rubble stone-work in mortar-, only 
differs from the first in the stones being laid or bedded in mortar, 
instead of being piled up without any connecting material. From 
the irregular shape of the stones, and the large spaces that conse- 
quently exist between them, this work consumes an immense 
quantity of mortar, and thereby becomes expensive. To obviate 
this, if the wall is not intended to be carried high, or has not a 
very heavy load to support, it is customary not to use mortar 
throughout the whole thickness of the wall, but merely to lay its 
external faces to the depth of 3 or 4 inches in mortar, and leave 
the middle part of the wall dry; and sometimes a dry rubble wall 
is merely pointed on its outsides with mortar forced into the joints 
by a trowel, and even this adds much to the stability and appear- 
ance of the work. 

870. Rubble-work in courses, is the same kind of work executed 
with greater care and attention, particularly in selecting stones of 
the same thickness for the external faces, so that the work may 



OP STONE-WORK OR MASONRY. 461 

proceed in horizontal layers or courses, which are nearly equal in 
perpendicular height. This work not only looks much neater, 
but is stronger and more durable, because as the stones are equal 
in thickness, they may be presumed to be equal in strength, and 
no one stone will have a greater tendency to break than another. 
Rubble stone-work, in all its varieties, is improved in appearance 
and stability, (especially mortar work,) by being chinked; that is, 
by having small wedges of stone driven by the hammer into all the 
larger interstices that occur in the joints, thus giving the stones a 
firmer and more solid bearing upon each other than they would 
otherwise have. 

871. Rubble stone-work is much used in all countries that 
abound in stone, particularly where it is not of the freestone quality; 
and of course the slab stones or those that divide naturally into 
flat laminae or plates, will produce stronger and better work than 
boulders or stones that present rounded surfaces to each other; 
but even these produce much sounder work than would be ex- 
pected, when the mortar is good; for many of the oldest churches 
and castles in England are built entirely of such materials, and a 
large part of the tower of London, its most ancient fort, or citadel, 
is of rubble-work; and many instances occur of flint stones, which 
are constantly of rounded forms, being the principal material used. 
Rough dry stone walling is the only fence or boundary between 
one field and another, or between estates, in the western parts of 
England, where rough stone abounds. It was much more used by 
the ancients than by the moderns, and its durability cannot be 
better proved than by the remains of it which still exist in many 
parts of Europe, notwithstanding that the ancients do not appear 
to have had great faith in its duration, for Vitruvius informs us 
the name by which it was distinguished among the Romans was, 
opus incerium. It is frequently used in England, on account of its 
cheapness, for foundations and plinths for heavy buildings; but 
this is a practice that ought not to be encouraged, unless the stone 
is very hard, and occurs in tolerably flat masses, because as stones 
of irregular shape can only bear on each other in points, instead 
of flat surfaces, there is a probability of such points crumbling 
away, which of course must produce a sinking and settlement of 
the work, if the superincumbent load is very great. 

872. Rubble stone-work, in all its varieties, is generally executed 
and valued by measurement, at an agreed price per rod or pole, 
in which case 18 inches is usually considered the standard thickness 
of a wall; and of course 16j feet is the length of a rod; but there 
seems some doubt, or difTerent local modes of computing, as to its 
height. There can be no doubt but that a square or superficial rod 
of work should be as high as it is long, or 16 J feet in each direc- 



462 OP STONE-WORK OR MASONRY. 

tion, or rather should contain 272 superficial feet, disregarding the 
quarter foot that arises out of the nnultiplication (122). But the 
writer has not met with any workman in the United States who 
would admit a rod of rubble stone-work to be 16j feet high. Some 
say that 16j feet long by 8 feet high, is admitted to be a rod of 
such work; and he has found others who contend that this work is 
measured like corded wood, and that 4 feet in height makes a rod. 
The only safe way, therefore, to make a contract for rubble stone- 
work is to specify the height that shall constitute a rod in the first 
instance, or what perhaps is still better, to agree how many cubic 
feet the rod shall contain; or even to have the work done at a 
price per cubic foot, without reference to rods, and then there will 
be no occasion to regard the thickness of the wall; while if the 
work is done by the rod superficial, 18 inches is the established 
thickness for a single wall; consequently should it be 3 feet thick, 
it will be paid for as two walls, or at double price; and 27 inches 
thick would be charged at the price of a wall and a half, and so 
in proportion for other thicknesses. 

873. The second variety of stone- work called solid wrought ma- 
sonry, is the best and most expensive that is executed; because it 
consists wholly of solid blocks of free-stone that are sawed, or 
otherwise cut, and made to fit close to each other in all their 
points, vertical as well as horizontal throughout, the whole thick- 
ness of the work. This kind of masonry is seldom used to any 
large extent, on account of its great expense; for it consumes an 
immense quantity of stone, as well as expensive labour, to reduce 
all the stones to perfectly flat sides. Solid masonry is therefore 
seldom executed in this manner, but all the external faces of the 
wall are formed of stones cut square, and of such magnitude as to 
run a considerable depth into the wall, and occasionally quite 
through it from face to face; and when the external surfaces of a 
course have thus been finished, all the internal vacuities are filled 
up with the smaller pieces of the stone, either square or irregu- 
lar, which are laid in mortar with great care to render the inside 
of the work as solid and regular as possible. Solid stone-work, 
executed in this manner, is often called mixed masonry, but it 
seems scarcely necessary to make this distinction, because in solid 
work this kind of rubble-work filling in should bear but a very 
small proportion to the solid square stones used, or the work will 
become ashlar-work, the next variety to be described. 

874. Solid masonry is made use of in building the stone piers of 
bridges, for stone columns, the side walls of canal locks, the founda- 
tions for large warehouses, and generally in all cases where the 
greatest strength, particularly resistance to pressure, is required; 
and it therefore requires particular care and circumspection in the 



OF STONE-WORK OR MASONRY. 463 

choice and selection of the stone, which should be of good and 
durable quality, and free from cracks or fissures, either natural 
or accidental. Great care should also be taken in forming the 
horizontal joints or beds, in order that the stones may bear 
throughout their whole surfaces, and not partially. On this head 
it becomes necessary to give the young Engineer a caution. 
There is no difficulty in getting the upper surface of a course of 
stone-work perfectly smooth and level if due care is taken in its 
formation; but in placing the next course upon it, workmen do 
not like the trouble of making the under sides or beds of the 
courses of stones that are to succeed, perfectly flat, and at right 
angles to that side of the stone that is to form the external face, 
but will generally only continue the right-angled direction for an 
inch or two next the face, and then give the remainder of the 
bed an angular direction, as shown in Fig. 165, PI. V., where a b 
is the upper level surface of a course of stone already laid, and c 
d the bed of one of the stones to be placed upon it, which, instead 
of being flat and level at its bottom in the direction of the dotted 
line, as it should be, is inclined upwards towards d, thus only pro- 
ducing perfect contact for the depth of an inch or two between c 
and a, and a considerable angular space between the two stones 
dii d c e, which has to be filled up with mortar, or even supported 
by chips or wedges of stone or iron driven in between d and e in 
order to support the stone, and bring its external face f c into a 
right lined direction with that of a. This mode of blocking up 
stones, as it is called^ is a common practice, but one which ought 
never to be tolerated when the work has to sustain a great weight 
from above. It produces a very neat and close joint on the face 
of the work, but without much solidity; because all the superin- 
cumbent pressure falls on the narrow joint, and upon the wedges 
and mortar, instead of upon the main body of the stone, conse- 
quently the wedges (if of stone) frequently crush to powder, and 
the sharp edges of the joint at c ^give way, and produce unequal 
and detrimental settlements in the work, by which its beauty and 
regularity are destroyed, and its strength impaired, owing to the 
breaking of the mortar joints. This mode of angular jointing is 
admissible in vertical joints, provided the spaces produced are 
but small, but even then it is better avoided, and ought never to 
be permitted in horizontal or bed joints. The breaking away of 
sharp edges (which in masonry and brick-work are always called 
quoins,) is sometimes prevented by bevelling the horizontal, and in 
some cases the vertical quoins of every stone to an angle of 45°, 
as shown at ^ A i in Fig. 165, and then the joints are said to be 
rusticated. 

Some other particulars relating to the building of stone- work 



464 OP STONE-WORK OR MASONRY. 

have to be noticed, but as they apply to the next variety of 
masonry to be described they vvill be introduced in that place with 
greater propriety. 

875. Ashlar masonry is the third and last variety to be described, 
and this, though not the best and most substantial kind of work, is 
more frequently used than any other, on account of its cheapness 
and its producing all the beauty and symmetry of solid stone- 
work, though destitute of a great part of its solidity and durabili- 
ty. It is, in fact, casing or veneering a common brick or rubble 
wall with wrought free-stone, so as to give it all the appearance 
of a building of solid stone. 

876. Ashlar stone-work is more or less worthy as it approaches 
more or less to solid masonry. It consists of building a wall or 
mass of common brick-work, or rubble stone-work, and facing it 
with pieces of wrought and squared free-stone, either on all its 
sides or generally on those sides that are to meet the eye. Thus 
if a house is to be built in ashlar-work, only the outer surface of 
the external walls would be cased with stone; because their in- 
sides have to be plastered or otherwise covered. 

877. No particular thickness is assigned for ashlar-work, con- 
sequently this is left to the choice of the builder; but as a general 
rule no stone facing less than 6 inches thick should be used, and 
ashlar facings generally run from this thickness to 8 or 9 inches, 
their length being from two to three feet^ and their height 9 or 
12 inches. The front face and four sides, i. e. the top, bottom and 
two sides of every stone require to be exactly cut and squared, 
that they may fit close to each other, but the back may be left 
rough and uneven, especially if the backing is to be of rubble- 
stone, but if of brick-work the stone should be cut smooth and 
flat. Some masons deem it an advantage to have the backs of 
facing stones angular to the face instead of parallel, in order that 
the backing may take hold of a part of the top or side of each 
stone instead of being applied to its back only. 

878. To build an ashlar faced wall, the facing stones must first 
be set accurately in their places bedded in mortar, and adjusted 
to their positions by the line and plumb rule, which, being done, 
the backing succeeds, and this is building a wall in bricks or rub- 
ble-stone immediately behind the stone facing and in close contact 
with it, taking care to fill in between the stone facing and the 
wall with mortar. This wall proceeds horizontally until it 
reaches the same height as the first course of stone, consequently 
if the backing is to be of brick-work, the height of the facing 
stones ought to be such as may agree exactly with a certain 
number of courses of brick-work, three or four courses, for ex- 
ample. The whole wall being thus brought to one height or 



OF STONE-WORK OR MASONRY. 465 

level, the second course of ashlar facing stones must be set upon 
the former course; and in doing this, a thorough stone or tail 
stone should be introduced at every interval of three or four feet. 
Thorough stones have been before stated (868) to be stones that 
run quite through a wall from face to face, but they are not ne- 
cessary unless the backing is of rubble work; and when brick-work 
is adopted, tail stones are used, which are stones usually about 
9 inches longer than the thickness of the facing stones, so that 
they present one of their ends to view in the outer face of the 
wall, and the other end tails, or runs about 9 inches into the 
brick-work, to bond with it, and thus prevent the facing stones 
from separating from the backing or filling-in work. The more 
effectually to obtain this object, the bed or under side of every 
tail stone, ought to come into contact with, or be very close to 
the upper side of the top of the facing stone over which it is 
placed, so as to admit a very thin mortar joint. In this manner 
the wall may be carried up to any required height, taking care 
to introduce bonding tail stones at proper intervals into every 
course, or every alternate course, according to the thickness of 
the ashlar facing, and the strength and durability that is intended 
to be given to the wall. 

879. In building wrought stone walls, the mortar joints are 
always very thin, so that the stones almost come into contact with 
each other. This could not be brought about if common mortar 
was used, on account of the coarseness of its component parts. 
Masons, therefore, use a mortar called water-putty, or fine stuff. 
It is the same as other mortar, but the slaked lime is passed through 
a fine wire cloth seive, and the sand, which should be of the purest 
silicious kind, undergoes the same treatment, and is used in much 
smaller proportion, though some masons use no sand at all with 
their lime. This mortar is applied in a softer or more fluid state 
than for brick-work, and the layer of it should not exceed the |^th 
of an inch in thickness when the stone is placed upon it. In Glas- 
gow and some parts of Scotland, wrought stone-work is frequently 
laid in oil putty, such as is used for glazing window sashes. This 
is made of finely powdered chalk, mixed to a proper consistency 
with linseed oil. This produces an unsightly appearance in newly 
executed stone-work, because the oil is absorbed by the stone, and 
gives a dark or dirty and irregular appearance to the joints, but 
it wears off and disappears in a few months, and makes a most 
excellent joint for strength and durability. 

880. Notwithstanding ashlar facing is the kind of stone-work 
more generally used than any other, it requires no argument to 
prove it to be a bad mode of construction, and one that is difficult 
to execute without considerable practice, so as to insure its stand- 

59 



466 * OF STONE-WORK OR MASONRY. 

ing without flaws or derangement of figure. No wall can be built 
of any considerable height, without its being subject to some sink- 
ing or settlement, owing to the mortar, while yet soft, giving way 
to the great weight that is accumulated upon it, especially in the 
lower horizontal joints; and this sinking will always be proportion- 
ate to the number of joints that occur. Now, in the stone facing, 
the mortar joints are not only less frequent, but are much closer 
or thinner than those in the backing, whether it be of rubble, or 
of brick-work. The facing will, therefore, be subject to little or no 
settlement, while the backing will go down considerably; hence a 
tendency exists to separate the two parts of the wall, and when 
the settling occurs in the backing, a great part of its weight is 
transferred to the projecting ends of the tail stones, causing them 
sometimes to break oif, and at others to lift or separate the joints 
of the face work, and often making it to bulge or project forwards 
out of the perpendicular right lined direction it ought to preserve. 
Skill and experience are, therefore, necessary in the performance 
of this work, in order to maintain the several parts in perfect ad- 
justment with respect to each other. The experienced bricklayer 
will know how much his work may be expected to settle, and will 
therefore keep his backing, in every place, so much higher than 
the face work, that although the upper surface of the wall may 
appear irregular during its progress, yet that it shall all sink to 
one common level soon after its completion — he will also take care 
to leave thick mortar joints over the tops of the tail stones, in order 
that the work, in sinking, may not fall directly upon them. With 
every care and precaution a faced wall is never as good as one 
that is built of equal sized homogeneous materials, so that level 
joints may run through the whole work in every direction, and 
that the joints, counted vertically, may be equal in every part of 
the wall. 

881. One thing of great consequence, that requires attention in 
masonry generally, whether it be rubble-stone, solid, or ashlar- 
work, is that all stones should be placed in the position of their 
natural beds, or in other words, shall stand in the work to which 
they are appropriated, in the same position as that in which they 
grew, or were produced in the earth. To those unaccustomed to 
the use and inspection of stones, it may appear impossible to deter- 
mine which is the upper or lower side of a block after it has been 
removed from the quarry and dressed up into shape; but the ex- 
perienced mason seldom feels any difficulty in determining this 
point, particularly if a stone has been some time exposed to the 
air and rains; for a more or less decided lamellar construction 
may, by attention, be discovered in all stones, and it is these lamel- 
lar stones that most particularly demand attention as to this mode 



OF STONE-WORK OR MASONRY. 467 

of using them. If a stone shows no character of this kind, the 
experienced quarryman, who understands his business, will always 
put his mark on that side of the stone that was uppermost in the 
earth. It is not so necessary in using stones to place the natural 
top upwards, for, in most instances, it will do quite as well if the 
natural position is exactly inverted, but no stone ought to be placed 
at right angles to its natural position, because if it is at all lamel- 
lar the plates cannot separate from each other when the burthen 
is so disposed as to press them into closer contact, but if the plates 
are in the direction of the pressure, they will not fail to separate 
from each other in process of time, or after frost, particularly when 
they are in external positions. This circumstance was either not 
understood, or not fully attended to, in the building of Blackfriar's 
Bridge, in London, and the inconvenience is much felt; for stones 
are found to burst out and shiver away after each winter's frost, 
thus occasioning constant labour and expense for replacing them 
with new stone. 

882. Little more can be said on the subject of building in stone, 
because the operation is so simple as to require no explanation, 
its execution requiring strength of apparatus combined with the 
greatest nicety of workmanship for its perfection. Still a few ob- 
servations on the manner of placing the stones, and fixing them 
in their positions, may be necessary. 

The stones being cut to their square shapes and dimensions by 
the stone-cutter's saw, are afterwards dressed and finished by va- 
riously formed steel chisels, urged by a small short handled wooden 
mallet; — any carving, letters, mouldings, or other ornaments that 
are to appear on the surface of the stone, are accurately drawn 
upon the face (previously made quite smooth) with hard black 
chalk, when they are worked out by these tools, drills of different 
sizes, rasps and tiles, and being finished, the flat parts of the stone 
are rubbed with a flat piece of stone, or if a moulding, by a piece 
of stone in which a similar or corresponding moulding has been 
sunk; and these being used with water and a little very fine sand, 
soon destroy any inequalities that may have been left, and pro- 
duce a fine regular surface. If the work has to be polished, this 
rubbing has to be followed by other rubbers of soft wood, and 
finally of buff leather, upon which polishing powders, such as 
emery, pumice-stone, chalk, polishing putty, &c. must be applied. 
In general, however, stone-work is left with what is called a rub- 
bed surface, or sometimes after being rendered flat and smooth 
without rubbing, it is chisel worked, that is, the whole surface of 
the stone is passed over with a sort of gouge tool, that cuts it into 
very shallow grooves or furrows, about f th of an inch wide, made 
close and parallel to each other. This is quite a matter of taste, 



468 OF STONE-WORK OR MASONRY. 

some thinking that the chiselled face looks handsomer than that 
which is rubbed smooth; but the fact is, the indentations are so 
shallow, that at three or four yards from the stone, it would be 
impossible to say whether it was rubbed or chiselled, except when 
the li^ht shines obliquely across the furrows. 

883. The stone being thus finished, must be carefully and deli- 
cately handled, so that none of its sharp corners, or angleS;, may 
be broken or chipped; and to insure this it must have the Lewis 
inserted in it, (469,) and be raised by blocks and a fall suspended 
from a set of shears, until a truck, or hand-barrow, can be got 
under it, when it is lowered on to it and conveyed to its destina- 
tion, where it is again lifted by another set of shears placed over 
the wall, and is thus brought exactly over the place where it is 
to be set, and bedded in mortar or putty. It is suspended about 
4 or 5 inches over the place it is to occupy, so as to allow the 
mortar to be thinly spread by a trowel, and when all is ready, three 
or four workmen lay hold of the corners of the stone to keep it in its 
proper vertical position, while the men at the rope slack out, and 
lower it very gently on to its bed. A few blows with a heavy 
wooden maul are then given to the end of the stone, in order to 
drive it into close lateral contact, or produce a close vertical joint 
between it and the stone previously laid, and the superfluous mor- 
tar, squeezed out of the joint by the pressure, being removed and 
made smooth by the sharp point of a trowel, the setting of the 
stone is finished. If the stone is moved from its first position on a 
truck by horses, it ought to be placed on a bed of straw and old 
sacking, to prevent injury to it; but the hand-barrow is the most 
safe and usual mode of conveyance, when the stone is not too heavy. 
The hand-barrow has no wheel, but is merely two parallel poles 
nearly three feet asunder, with a flat boarded platform to receive 
the stones between them. It requires two men to work it, and 
they walk between the poles, or for greater weights four men are 
employed, one at each end of each pole; or six men can apply their 
strength by four walking on the outsides of the poles, and two 
between them. 

884. Mr. Smeaton in his published account of the operations 
and proceedings during the building of the Eddystone light-house, 
describes a most excellent form of shears that is simple and admi- 
rably suited to the moving and placing of heavy stones on walls, 
or other buildings. It consists of three pieces of timber disposed 
in the form shown at Fig. 166, the bottom piece h is square, and 
may be from 12 to 15 feet long, and should be sound and hard. 
The shears consist of two poles onlv ii which may be round, 
tapering, and as long as they can be conveniently obtained, say 
from 18 to 30 {^^i. Their lower ends are connected with the bot- 
tom piece h by two very strong iron eyes or links, loose enough to 



OF STONE- WORK OR MASONRY. 469 

permit motion, while their upper ends meet, and are connected 
by the strong iron pin k which passes through both of them, and 
aJso serves to support the top hook of the blocks and fall /, the run- 
ning rope of which passes downwards from the upper block, and 
takes a course close to one of the poles and is passed through the 
snatch block m, fixed to the bottom piece h, and to this rope the 
workmen apply their strength immediately, or through the agency 
of a crab, or windlass, according to the force to be overcome. The 
central point of the horizontal piece h is marked on its top, at 
the point to which the bottom block would descend, when the piece 
h is set truly level. To use this apparatus the bottom or founda- 
tion piece h is set truly level upon hard ground, or is supported on 
piles or timber skids, if the ground is not hard enough to sustain 
the load; and the poles are retained in their vertical or other re- 
quired position, by two sets of running blocks and falls, pulling in 
opposite directions, and at right angles to the direction of the 
length of the foundation piece h, as may be better seen in Fi^. 
167, which is a perspective view of the same machine as fixed for 
use. The upper ends of the guy blocks are attached to the tops 
of the poles, and their lower ends to strong posts fixed in the ground, 
or to stumps of trees, parts of buildings, or any thing that will 
afford stability. Then by lowering out the fall n, and tightening 
that at 0, the shears may be made to incline or bend over, as shown 
in the figure, until the bottom block p hangs directly over a stone 
r that has to be lifted, and thus this stone may be taken off the 
ground, and raised to any required height, by the principal blocks 
and fall jD q. That donje, the guy fall o is slacked while n is tighten- 
ed, so that the shear poles are first brought into a vertical position, 
and are afterwards allowed to turn over or incline to the other 
side, as shown by the dotted lines q q, when the sustaining force 
will be transferred to the guy fall o, and n will become useless, and 
in this way a stone may be brought from the ground upon which 
it was worked, directly over the place s in the wall in which it has 
to be deposited, without disengaging it at all from the block by 
which it was first lifted, and without hand-barrows, or any trou- 
ble whatever. To insure the delivery of the stone into its proper 
place by this machine, a line must be strained from the centre of 
the stone to be moved, to a point perpendicularly under the centre 
of the place in which the stone has to be placed, and the founda- 
tion piece h of the shears must be moved until its central marked 
point t falls under that line, while the length of the piece is at 
right angles to it; the foundation piece vnust then be fixed in this 
position by driving short stakes round it into the ground, and then 
the upper end of the shears in moving will describe an arc of a 
circle v v, the plane of which will pass through the centre of the 



470 OF STONE-WORK OR MASONRY. 

stone, and the centre of the bed or position in which it is to be 
placed. 

885. A machine somewhat similar in principle, but different in 
construction to that just described, is much used in Philadelphia 
and the northern cities, for raising heavy stones in building. The 
bottom piece h, Fig. 166, is still square, but not so long as has been 
described, and has several small but very strong cast iron wheels 
let into its under side, so as to make the machine easily moveable 
in a longer bed plate that rests on the ground, and is grooved out 
to receive the wheels, and prevent their slipping. The upright 
poles are longer than those described, and are put much closer to- 
gether and nearly parallel, and they are united throughout their 
whole height by rounds or steps, so as to form a ladder. The poles 
do not on this account meet at the top, and their lower ends are 
permanently morticed into the bottom piece h. The machine 
when fixed in its place, has its wheels wedged up to prevent its 
moving laterally, and is retained in its nearly upright position by 
guy ropes, or falls, as before described, but from the proximity of 
its poles, and the steps that unite them no stone can pass between 
them, and therefore although it is an equally convenient machine 
for raising stones from the ground in front of a wall, and placing 
them upon such wall by altering its inclination, still it is incapa- 
ble of moving stones through so large a range of space as the former 
machine. This apparatus does not turn over, but always works 
with an inclination on the same side of the perpendicular. 

886. To make a stone wall look regular and handsome, the 
stones ought to be as nearly of the same colour, quality, and 
dimensions as possible, but as stones of the same size cannot often 
be procured, some arrangement has to be adopted by which sym- 
metry of appearance may be produced; thus if the courses cannot 
be had of the same height, the highest stones should be used near 
the base, and they may decrease in magnitude regularly as the 
work proceeds upwards. The ancients considered the equal 
courses as forming the handsomest work, and according to Vitru- 
vius this arrangement was called Isodomum. No variation in the 
height of a continuous course can possibly be admitted; but courses 
of different heights are very frequently made to alternate with 
each other in succession, and this was called Pseudisodomum, and 
has a good effect. Great care is necessary in placing the vertical 
joints so that no two shall ever be allowed to come over each other 
in contiguous courses, and yet they ought to come directly over 
each other in every alternate course. This will easily be brought 
about if all the stones are of the same length as in Fig. 168, be- 
cause then the vertical joints will all fall directly in the middle of 
the stones above and below them, if stones of half length are used 



OF STONE-WORK OR MASONRY. 471 

to commence every alternate course. If, however, the stones so 
disposed have not sufficient magnitude to reach quite through the 
wall, and two vertical lines of work should be necessary, this will 
be a bad disposition of the materials, because a straight vertical 
joint will exist between the two faces of the wall, without any 
thing to tie or connect them together, and such a wall will be 
very.aptto split longitudinally. To obviate this, thorough stones, 
called diatonos by Vitruvius, must be introduced frequently, or at 
all events tail stones, which will nearly traverse the wall, and this 
will be produced by placing one stone with its length in the direc- 
tion of the wall, and the next with its length across it, as in Fig, 
169. When a stone presents its small end in the face of the wall,, 
as in this example, the end is called its head, and the stone itself 
is called a header; while a stone showing its greatest length is called 
a stretcher: hence this mode of building is often called header and 
stretcher work. 

887. The ancients were very partial to a disposition of joints, 
such as is never adopted in modern work, although Vitruvius 
speaks of it as the most handsome in appearance. In this the 
stones are all square and of uniform size, and the face joints in- 
stead of being horizontal and vertical, are inclined in angles of 
45° to the horizon, the transverse joints alone being level. This 
gives an appearance of net- work to the face of the wall, and was 
on this account called reticulated work by the Romans. Its ap- 
pearance is shown at Fig. 170, but it has not a single good quality 
to recommend it, and on this account has fallen into disuse. The 
Emplecton of the Romans was a wall similar to one of modern 
ashlar facing, except that the wrought facing was carried up on 
both faces instead of one side of the wall only, while the central 
part was backed up or filled in by rubble-work only. The walls 
of the celebrated Pantheon at Rome, are a fine example of this 
kind of building. The emplecton of the Greeks, on the contrary, 
was a completely solid stone wall with no rubble-work in it, but 
all the internal filling in stones were squared and dressed so as to 
form the best, most solid and durable of all walls. 

888. With a view to give greater strength and security to walls 
that are built of stone, it was customary with the ancients (and 
that custom has been continued,) to use attachments of metal to 
tie or connect the several stones together, such pieces being call- 
ed cramps^ cramperns, or cramp-irons. They are made in differ- 
ent forms, suited to the purposes to which they are to be appro- 
priated, and then obtain different names, such as dowell cramps, 
dovetail cramps, cauked or cogged cramps, and chains. The 
dowell cramp is used in ashlar facing to secure the vertical stones 
from getting out of their positions; and it is often used, with a like 



472 OP STONE-WORK OR MASONRY. 

view, in horizontal joints, to prevent stones from sliding or moving 
from the places in w-hich they are set, so as to injure the appear- 
ance of the finished face of the work. The dowell cramp is 
merely a piece of round or bolt iron, from |- an inch to 3 inches 
in diameter, and from 1 inch to 12 inches in length, according 
to the thickness and size of the stones made use of, the two ends 
of which are let half the length of the cramp into two holes. that 
are drilled into the contiguous faces of the stones exactly opposite 
to each other; so that if we conceive Fig. 168 to represent a 
piece of ashlar faced work instead of solid masonry, v v will show 
the positions of the dowells in the vertical joints, and x x those in 
the horizontal courses, w w Are two dowells fixed in the top 
course to pass into the beds or under sides of the next course of 
stones to be laid. The holes for receiving these dowells ought to 
be very little larger than the metal pins that pass into them, so as 
not to permit them to move, and in light work the dowells are 
set or fixed in soft or nearly fluid plaster of Paris and water, but 
in heavy work they are run in with very hot melted lead. When 
this has to be done a very small channel is carved out between 
the faces of the stones that are to be contiguous, for introducing 
the lead, and a small cup or funnel is formed at the end of the 
channel with damp clay to receive the lead from the ladle. This 
channel must take a perpendicular direction, or an oblique one to 
the back of the work, in order that it may be covered and hidden 
when the work is finished. Stones thus dowelled together cannot 
break away or quit their positions, unless a part of the stone 
gives way. 

889. In Fig. 171 a dovetailed cramp is shown at v. This may 
be made of cast or wrought iron, and is a flat plate of metal vary- 
ing in dimensions with the strength required from it, and it de- 
rives its name from its two ends spreading out into a form like the 
tail of the dove or pigeon. A cavity corresponding exactly with 
the size and shape of the cramp, as at u, is sunk, half in one stone 
and half in the other, so that the cramp may be sunk rather 
more than its own thickness into the two stones when it is bedded 
in melted lead within a joint, and of course does not appear ex- 
ternally. The form of a caulked or cogged cramp is shown at y 
in the same figure. This is merely a piece of square bar iron 
bent down or cogged (generally called corked by workmen,) at its 
two ends to a sufficient length to take good hold of the two stones 
into which it is inserted, as before described, by sinking a cavity 
into the two stones large enough to receive it, as indicated by the 
dotted lines below it in the figure, and then it is run in with lead. 
The two last described clamps are those that are constantly used 
for connecting the flat coping stones with which walls are fre- 



OF STONE-WORK OR MASONRY. 473 

quently covered, and stone cornices should be crannped in the 
same manner. Cramps are always employed in works that re- 
quire great solidity, as in the piers and abutments of bridges, and 
the voussoirs of large arches, and all external work liable to be 
injured by weather should be cramped. Iron is used in modern 
buildings, but the Romans, who were accustomed to employ 
cramps in the greatest profusion, used brass or bronze, a material 
much more durable than iron, and not so liable to rust, which is 
the greatest objection to the use of cramps in external work; be- 
cause even though they may endure a long time, the oxide of 
iron ^discolours the rain-w^ater that falls upon it, and produces 
very ugly yellow and brown stains, which greatly disfigure the 
work. In all places where this is likely to happen, it is, therefore, 
much hetier to use cramps of gun metal, (643 and 737,) and as 
these can be cast from a pattern, the expense of forming them is 
small, and we have an assurance of their all being of the same 
size, which saves trouble to the mason in sinking his holes. Chain 
cramps are only used for tying large masses of work together, and 
are applied in addition to the detached cramps before described. 
The chain may be made of links as usual, or may consist of a 
single bar of iron united at its ends into a hoop, and with project- 
ing collars or knobs welded on to it at short intervals. The whole 
is let into a groove or cavity in the upper surface of the course 
of stones to which it is applied, so that the work is hooped or 
bound together. Sir Christopher Wren used two cramping chains 
below the springing of the dome of St. Paul's Cathedral in Lon- 
don, in order to resist and distribute the lateral pressure of so im- 
mense a load, for this dome is 145 feet in diameter, and 240 feet 
high from its springing to the top of the large stone lantern and 
cross which surmount it. Sometimes when the work requires to 
be more than ordinarily solid, not only cramps and chains are re- 
sorted to, but the stones instead of having flat joints applied to 
each other, are so shaped that the side of one stone may dovetail 
or lock into the side of the other. When this construction is 
adopted, every stone, after the first, has to be lowered perpen- 
dicularly into its position, and cannot afterwards be removed by 
any lateral force that is not strong enough to break and tear to 
pieces some of the stones of which the course is composed. Mr. 
Smeaton adopted this mode of joining the stones in the erection of 
the celebrated Eddystone light-house, built by him between June, 
1757, and October, 1759. This light-house stands on a detached 
and isolated point of hard rock, rising out of the Atlantic Ocean 
nearly S. S. W. from the important port of Plymouth, in England, 
and only 14 miles from it. The rock is so small as to be invisible 
at a short distance, and having 30 fathoms water all round it, 
60 



474 OF STONE-WORK OR MASONRY. 

vessels used formerly to strike upon it, and were lost before they 
were aware of any danger. The exposed situation of this rock, 
and its inclined direction, both above and under water, makes it 
subject to most heavy and violent seas, so that it was thought im- 
possible to erect a permanent light-house upon it, to warn mari- 
ners of their danger. In 169G the first erection was attempted, 
and was finished in four years. The building was of stone, eighty 
feet high from the rock, and was designed and executed by a Mr. 
Winstanley, a gentleman of great mechanical genius, and after it 
had undergone considerable alterations and improvements it was 
thought to be so strong that nothing could aflfect it. Mr. 'Win- 
stanley, in his account of this extraordinary building, however, 
states that he had seen the sea, in times of violent gales, fly, in 
appearance, a hundred feet above the vane on the top of the 
building, and on the night of the 26th of November, 1703, it was 
carried wholly away by a violent storm, while Mr. Winstanley 
and many of his friends and workmen were in it, being just then 
on the eve of its completion. Not a trace of it or its remains were 
ever after heard of, except only some very heavy iron ties that 
had been fixed into the rock to assist in holding it down. From 
these it broke away, and it is thought to have been overset in an 
entire piece, breaking off from its attachments to the rock. Very 
soon afterwards a second light-house was erected by a Mr. Rud- 
yerd, which was a frustrum of a cone 23 feet 4 inches diameter at 
the base, rising to a total height of 92 feet, in which it diminish- 
ed to a diameter of 14 feet 3 inches. This second building was 
altogether of timber, and has been much extolled for the strength, 
excellence, and skill of its framing. It must, indeed, have been 
well contrived, for it endured forty-six years without symptoms of 
failure, and then was consumed by accidental fire, originating in 
some want of attention to the candles which were then used in 
the top lantern for producing the light. This accident happened 
to it in December, 1755, and in June, 1757, Mr. Smeaton com- 
menced the present building, which is admitted by all competent 
judges to be a chef d'oeuvre of modern engineering, at least in this 
department of work. Mr. Smeaton kept a journal of his thoughts 
and proceedings while carrying on this most difiicult and perfect 
piece of workmanship, and it was published after his death in a 
very large folio volume with many plates. In this work every 
minute particular concerning the progress of the work, and the 
difficulties met with, are described with the most minute detail, 
and in such manner as cannot fail to be interesting and useful to 
the practical Engineer. This book is high-priced and scarce, but 
may be found in many public libraries, and a careful perusal of 
it is strongly recommended to such as may have an opportunity 



OF STONE-WORK OR MASONRY. 475 

of meeting with it. Eddystone light-house is circular on the plan, 
cylindrical near its top, and swells at its lower part into a para- 
bolic conoid. Mr. Smeaton observes, that he took the hint of this 
form from noticing the shape that the trunks of old oak trees 
assume, and the power they have of withstanding high winds, 
notwithstanding the great surface their tops expose to its eifects. 
As the proposed building was to cover nearly the whole top of 
the rock, and a part of that had great inclination, the first thing 
to be done was to cut this sloping part into horizontal steps, a 
work that had been partly carried into execution when the 
former buildings were executed. These steps were to serve as 
level foundations for courses of stone that were laid upon them, in 
the form of segments of circles, each succeeding one approaching 
nearer to a complete circle, until by seven such segmental 
courses the foundation was brought to a general level, after 
which the future courses were complete circles. In this manner 
the building was carried up in perfectly solid masonry to the 
height of 35 feet 4 inches above the base by 14 courses or layers 
of stone, of an average diameter of 22 feet at the middle point of 
this height. These courses were not only laid in the best cement, 
but were prevented moving from their places by eight strong per- 
pendicular dowells formed of square blocks of the hardest marble, 
introduced at ^ of the radius from the outside, and a still larger 
one in the centre; and the stones were not only cramped and 
pinned or dowelled together, but all the stones of each course 
were dovetailed into each other in the manner shown at Fig. 
172, so that no one stone could separate from another. Each 
succeeding course was so far twisted round in its horizontal direc- 
tion that the zigzag radial joints of one course came over the 
solid stones of the next below it. This solid work was carried up 
to such a height as was thought would raise it above the force of 
the waves of ordinary seas. The entrance door was placed upon 
the top of this solid work, and was approached by a moveable 
ladder. Four circular apartments succeeded, the two lowest of 
which were store rooms, the next a kitchen with a fire place, and 
the uppermost a sleeping chamber, and this was surmounted by 
the lantern, an octagonal chamber ten feet across, the sides of 
which were copper, and iron sashes glazed with strong glass for 
containing the lights. Each apartment is separated from the 
other by a vaulted roof of stone with a flat top, forming the floor 
of the room above it. The same process of dovetailing the stones 
into each other is preserved in all these vaults and floors, in addi- 
tion to which two endless chains are sunk into the stones that 
surround the abutments of these vaults to resist their lateral 
thrust. This short notice cannot pretend to do justice to the 



476 OF STONE-WORK OR MASONRY. 

account of this curious and interesting building, and is only intro- 
duced here to show the care and precaution that should be used 
in constructing stone buildings, when they are intended to be very 
durable or to resist great strains. 

890. One of the most important uses of stone is for construct- 
ing large arches for bridges and other purposes; but a large arch 
cannot be built without timber centring to support it during its 
progress, and this in some measure connects this subject with car- 
pentry. For this reason, and because the building of arches in- 
volves principles quite different from those that apply to perpen- 
dicular walls, nothing is said upon them in this place, but a sepa- 
rate chapter will be devoted to their consideration after the lead- 
ing principles of carpentry have been explained. 

891. Wrought stone-work is not only used by itself, but is fre- 
quently mixed in small quantities with brick-work for the double 
purposeof producing strength, and adding to the beauty of appear- 
ance. Thus in the handsomest brick buildings the sills, or lowest 
member of each window, should be of cut stone — steps leading to 
entrance doors should be of the same material — a plinth or surbase 
of from 2 to 3 feet high of wrought stone, is often used next the 
ground, before brick-work commences. Straight horizontal lines 
of stone, of 6 or 9 inches wide, and plain or carved, are frequent- 
ly introduced across the brick front of buildings, between the tops 
and bottoms of windows, to break the monoscopy of appearance, 
and these are called string courses. Brick semicircular arches are 
frequently made to rise, or spring from stone imposts, or horizon- 
tal springing pieces, and key stones of stone are often introduced 
into the centres of such arches. Stone pilasters and cornices are 
likewise not uncommon, and every well finished wall ought to be 
coped or covered with long plates of stone, about 4 inches wider 
than the wall is thick, so as to project or oversail the wall about 
2 inches on each side, to throw rain away from it. In all these 
cases (except steps) the face of the stone should project from one 
to two inches beyond the face of the brick-work, to produce a 
handsome and bold effect. The upper projecting surface of such 
stones ought not to be level, but should be bevelled downwards to 
throw off water; and stone so bevelled is said to be weathered. The 
flat underside of these projecting stones should have a shallow 
longitudinal groove sunk into it, about J an inch from its front side, 
to prevent the water that may hang to its lower edge from get- 
ting irrto the wall. Such groove is called a throat, or the stone is 
said to be throated, and all coping stones should be throated along 
both their edges. Coping for common work is made of slab or 
lamellar stone, like Yorkshire paving or North River stone, and 
then it is called parallel copi7ig, and it should be set a little out of 



OP STONE-WORK OR MASONRY. 477 

level to throw the water to the front or back of the wall, as may 
be most convenient. The best coping is made out of sawed free- 
stone, so cut that one edge may be an inch thicker than the other, 
io produce weather, or throw the water off The parapet, or side 
walls of bridges, are generally covered with coping that is an inch 
or two thicker in the middle than on either side, so that the water 
runs both ways, and such coping is said to be saddle hacked. 

Wrought stone is not only used for building walls, foundations, 
and such things as have been already noticed, but likewise for 
forming columns and pilasters with their capitals, pedestals, bul- 
lasters for bridges and terraces, cornices, pediments, cantilevers, 
and many ornamental purposes; but as these belong more particu- 
larly to the province of architecture rather than engineering, 
they must be passed over without notice. Some terms and ope- 
rations, that apply in common to masonry and brick-work, will be 
explained in the next section, which treats on this latter subject. 

Of the Measurement of Wrought Stone-ivork. 

892. If stone is bought or transported by weight, such weight 
may be pretty accurately determined by consulting the table of 
specific gravities (861). Free-stone is, however, generally sold by 
cubic, and slab, or paving stones by superficial measure, the price 
varying with the goodness and dimensions of the pieces; for iars:e 
stones (owing to the difficulty of getting them out of the quarry 
without shakes or flaws, and of moving them afterwards) are worth 
considerably more per foot, than the same stone in smaller pieces. 

Paving stone, though sold by superficial measure, is brought out 
of the quarry with rough edges, and has always to be squared by 
the saw or chisel, and its upper surface frequently requires to be 
tooled or rubbed to a flat face, and such operations are always ad- 
ditional charges, computed by superficial measure. Coping stones, 
string stones, and such kinds of stone-work as contain the same 
quantity of stone, and labour, in equal lengths, are usually sold by 
the foot, running measure, at prices depending on the quality and 
value of the stone, its magnitude, and the degree of labour or 
finishing that has been bestowed upon them. Throating is paid 
for by the foot run, and holes sunk for admitting iron railing, or 
for pins, dowells, or other cramps, at a certain sum for each hole, 
or each dozen holes, the mason finding his own tools. Masons' 
tools, such as chisels, drills, mallets, and other small articles, are 
so frequently lost or mislaid, that it is better for the workman to 
find such tools for himself; but all large implements, such as saws, 
tressels, or benches, barrows, shears, blocks and fall, long level, 
&.C. are provided by the master or employer, who also pays 



478 OF STONE-WORK OR MASONRY. 

smith's charges, or the blacksmith's work for sharpening and re- 
pairing such tools as are deranged by fair use. 

893. Wrought stone-work is among the most expensive of all the 
building processes, on account of the weight of the raw material, 
the cost of its transportation, the workmanship requiring good and 
experienced hands at high wages, and ;ill their operations being, 
from the nature of the material, slow in their progress. The 
harder stones, such as granite and sienite, are frequently cheaper 
than the softer free-stones, because they can be got out of the 
quarry, and are dressed there to very nearly their required forms, 
for much less prices than the masons of cities could do the same 
quantity and quality of work for. The soft free-stones are de- 
livered from the quarry in large square blocks, to be afterwards 
cut up, and converted as may be required. They are first paid 
for as cubic stone at the quarry, according to the measurements 
usually marked on each block. On their arrival at the mason's 
yard they are sawed into square blocks, slabs, ashlar blocks, and 
various scantlings, as may be required, and this sawing, which is a 
slow operation, is paid for by the superficial measure of the surface 
exposed by the cuts, and such work is called plain work — any 
thing is also called plain work that is finished with a flat surface, 
whether produced by the saw, by chiselling, or other means. 

894. The thin edge of a piece of stone is very often worked 
into the form of a moulding to project over a plain surface for 
forming cornices, architraves, and other ornamental finishing, and 
such work is called moulded work. As such mouldings could not 
be set out or lined for the workman, upon a rough and uneven 
surface, so the mason is entitled to charge for superficial plain 
work before the moulding is commenced, and then the moulded 
work is a separate charge. Mouldings are also paid for by su- 
perficial measure, according to what is called their girt. To ob- 
tain this, a piece of fine twine or thread is applied to the top or 
bottom of the moulding, is pressed down into all the cavities, and 
forced into all narrow chinks or quirks, and strained over protu- 
berant parts until the opposite side of the moulding is reached, 
when the string on being opened out will give the superficial 
breadth of the whole moulding, and this being multiplied by its 
length will express its entire superficies to be charged for. When 
mouldings return at right angles, and are mitred, or are made to 
meet at an angle of 45°, the w'orkman is entitled to the extreme, 
and not the least or even the mean measurement of the moulding. 

895. When mouldings are worked upon a stone that is to ex- 
pose a flat surface with the moulding projecting above it, the flat 
surface of the stone must evidently be sunk or cut away to a depth 
equal to the projection of the moulding, and such work is called 



OF STONE-WORK OR MASONRY. 479 

sunk plain work, and is charged at a price increasing with the 
depth of the work, or quantity of stone that has been cut away 
and the difficulty attending its execution. Likewise when a sunk 
pannel, surrounded by a moulding, is introduced into a flat surface, 
that pannel would be sunk work, but the moulding, moulded 
work, and the entire surface would be first measured and allowed 
for as plain work. 

896. If a stone column, or pillar, has to be formed, superficial 
plain work is allowed in the first instance upon all the six sides of 
each block of stone, because the top and bottom of each block 
must be made fair and flat, that it may fit to the other stones 
above and below it; and as these joints must be at right angles 
with the outside of the column, or at any rate with its axis, so 
these joints cannot be accurately set out unless the four upright sides 
are made flat and smooth. A skilful mason can, however, set out 
and square these joints after one of the upright sides of the stone 
has been rendered flat and smooth, and it is a common practice 
to do so; but still as custom has established the practice of charg- 
ing for all four of the sides at plain work price, masons always 
expect this charge to be allowed to them. All architectural 
columns taper, or are slightly conical, therefore to set out a column 
for work, the centre of each block of stone must be found upon 
the two sides that are to become its top and bottom; and from these 
centres, circles are struck corresponding to the circular area of 
that part of the column that such stone is to form, which done, 
all the solid angles, and other parts of the block exterior to the 
circles, are chopped away, and the stone is then chiselled down 
to the cylindrical or nearly cylindrical form, and this is called 
plain circular work. If a fillet, or other ornament is to appear 
upon the column, and project from it, this will be circular mould- 
ed work, and as the shaft of the column above and below it must 
be diminished, what is taken otF it will be sunk circular work; 
and should the column be fluted, the sinking of the flutes will be 
of the same kind. Circular work, in its several varieties, being 
more difficult to execute than plain work, is paid for at a higher 
rate. These several varieties of work, at diflferent rates of charge, 
make the measurement and valuation of highly finished masonry 
intricate and troublesome, and greatly advance the cost of its 
execution, because first, the rough stone has to be cubed and paid 
for; next, the plain work on its surface; next, sunk plain work, 
moulded work, circular work, &c. &c.; thus requiring the same 
surfaces to be gone over and over again in different dimensions, 
and at different prices. The working out is therefore tedious, but 
the operation is very simple when understood, because it only 
amounts to common cubing in the first instance, and to squaring 



480 



OF STONE-WORK OR MASONRY. 



superficial dimensions afterwards. As, however, the Engineer will 
seldom have to measure and value stone columns and richly orna- 
mented architectural work, a single example of a plain stone wall 
will be sufficient to illustrate the application of the above men- 
tioned principles to practice. 

897. Let it be required to measure, and determine the value of 
a piece of ashlar stone-work 12 feet long, 4 feet high, and 6 inches 
thick, in 4 courses, containing 10 upright joints, without any tail- 
ing stones, so that the stone-work shall be of the same thickness 
throughout. First, to determine the quantity of stone, each stone 
may be separately cubed, or, what in this case is a shorter process, 
the whole stone may be cubed at once by multiplying its length 12 
feet, by its height 4 feet, making 48 feet super., and this again 
by 6 inches for the thickness, gives 24 feet, cube, of stone. But 
small ashlar stones, when all of the same sectional area as in the 
example, are more frequently sold by the running foot; therefore 
the dimensions and particulars may be entered in the measuring 
book as follows: — - 



Ft. In 
4)12 



12 

4 



8)12 
6 



10) 1 
6 



48 



48 



48 
5 



53 



Run of 6 inches rough ashlar 12 inches wide, at 48 cents, 



Super, plain face and rubbed, at 45 cents, 



J 



Beds, 

Upright joints, 

Super, plain beds and joints, at 30 cents. 



$ ds. 
23 04 



21 60 



15 90 



$60 54 



Thus it appears that 48 superficial feet of such work will cost 
^60 54 at the prices set down, or if that sum is divided by 48 it 
will show that each foot of such work comes to $1 26. 

898. To understand the above mode of entry, it must be kept 
in mind that in measuring artificer's work of every kind, when a 
figure is set before a sum, and separated from it by a bracket or 
parenthesis, as in the case with the 4) and the l^ft. 0, at the 
commencement of the entry, the separated figure shows that the 
dimension following it is to be repeated or multiplied so many 
times; and as the question supposes that there are 4 courses of 
stone each 12 feet long, so 12x4 give the entire length, in running 
measure, of stone used in the whole work, or 48 feet, which is set 
down in the second column, and a line is drawn under these two 
columns of figures to indicate that they are done with. 

The first column next contains 12 ieet with its multiplier 4 



OP STONE-WORK OR MASONRY. 481 

feet placed under it, showing that 12 feet, the total length, is 
multiplied by 4 feet, the total height, producing 48 feet, the total 
number of square or superficial feet of plain work existing in the 
front or face of the wall, and this product is also inserted in the 
second column, and another line is drawn under these figures for 
a like purpose. 

Then 12 feet, the length, is again set down with 6 inches under 
it, as its multiplier, because the stone is 6 inches thick, and the 
product would give the area of smooth surface in one horizontal 
joint. But as the work consists of 4 distinct courses, the top and 
bottom surface of each course has to be taken, therefore this 
quantity is preceded by 8,) showing that the product of 12 feet 
by 6 inches must be taken 8 times, which produces 48 feet super- 
ficial of bed, or horizontal surface, and this product is put in the 
second column and a line drawn. 

Lastly, 1 foot, the height of a course, is multiplied by 6 inches, 
the thickness of stone, and as 10 vertical joints occur, so 10) ia 
placed before these figures to indicate that the product of 1 foot 
by 6 inches must be taken 10 times, producing 5 feet in the 
second column; and as the 48 feet and 5 feet are both dimensions 
of the same kind, and at similar prices, they are joined by a cir- 
cumflex and added together, making 53 feet superficial for the 
total quantity of horizontal and vertical jointing in the whole work. 

899. The prices to be set against these several varieties of 
work, and indeed every kind of builders' work, can only be accu- 
rately determined by taking the cost of the raw material before 
any labour is bestowed upon it, and adding thereto all expenses 
upon it for transportation and other incidental charges, then mak- 
ing an allowance for the waste that always arises in cutting largje 
pieces into smaller ones, then adding the net cost of workmen's 
wages for converting it into shape, adding thereto the expense 
incurred for nails, glue, screws, solder, or other materials used, 
and lastly, adding a per centum charge upon the whole for the 
master's profit, which must be large enough to cover the wear, 
tear, and destruction of tools, shop rent and firing, and interest of 
the money expended, provided credit is given upon the work. 
This allowance is usually from 15 to 20, and sometimes 25 per 
cent, upon the actual cost, which may appear a large profit, and 
would be so was it all profit. But when it is considered that the 
master mechanic makes no specific charge to his employer for 
the rent of the large premises he frequently occupies, for the fires 
he is obliged to use in different processes, for the tools he has to 
provide, some of which are costly, and all constantly wearing 
out, or getting broken in use, that he often takes great risk upon 
himself, and has to pay his workmen weekly in cash, while he 
61 



482 OP STONE-WORK OR MASONRY. 

himself has frequently to wait twelve months or more for his 
money, the prolit will be found far from excessive, and in some 
cases even too moderate. 

900. It will thus be seen that setting prices upon work is not 
an easy task, and cannot be done at all with anything like pre- 
cision, without some knowlege and experience of the nature of 
the work to be valued. To assist the builder and surveyor in 
their operations, books are published under the title of Build- 
ers' Price Books, and they render great aid. Thus in London, 
and for some distance around it, builders regulate their prices 
either by Crosby's or Taylor's Price Book, both of which are pub- 
lished annually like almanacs, and contain the prices for which 
all the various operations connected with building have been per- 
formed in the past year, as well as the prices of materials, and 
many tables and remarks that are highly useful to Builders, Engi- 
neers and Architects; and a similar work is now published in Bos- 
ton, called Gallier's American Builders' Price Book and Estimator, 
which is replete with useful information, insomuch that such a 
hook should be in the hands of every young Engineer and Archi- 
tect, for the sake of the minute and particular information that 
is conveyed respecting the measuring and pricing of every kind of 
work and material, as well as for becoming acquainted with the 
technical phraseology that is applied to the various kinds of work 
or parts of the same work, which details cannot be found else- 
where. Still, however, the prices quoted for work in these books 
must not be relied upon, or applied to similar work in distant 
places, for no such book can be general. A price book published 
in London, Boston, or any other city, may give true and faithful 
accounts of the prices for which work should be executed at or 
near to those places, and may therefore be confided in at home. 
But it often happens that in a less distance than 100 miles the 
price of materials and rate of wages, owing to local circumstances, 
may be quite different, consequently different prices must be 
allowed. London and Boston are both shipping ports and popu- 
lous cities, abounding with the best workmen of every description, 
who, by being constantly occupied in the same operations, acquire 
the greatest readiness and expedition, combined with perfection 
of workmanship, in their several departments. They have also 
the advantage of every facility that good tools and machinery can 
afford them, and buy their raw materials at first hand where 
competition exists, and therefore at the cheapest rates. A sum, 
therefore, that would be amply sufficient for an artizan in such 
cities might prove a starving price to an inland workman having 
none of these advantages; for although he might do the work as 
well, he would perhaps take twice as much time for its perform- 



OP BRICK-WORK. 483 

ance, and would probably have to pay much higher for his mate- 
rials. Whenever, therefore, a price book is used out of the place 
for which it is intended, the prices it quotes both for materials 
and labour or wages, ought to be compared with the prices and 
rates of the place where it is used, when it will show how much 
ought to be added or subtracted from the prices it gives, in order 
to obtain local prices of the place, and price books thus used will 
prove very useful, and save a great deal of trouble. 

901. The example of measuring the ashlar-wall before given, 
(897,) is extracted from Gallier's Boston price book, page 22, and 
is here referred to again, because it appears that there is either 
a mistake in one of the dimensions, or that the American method 
of measuring wrought masonry differs from the English. But the 
writer has not had sufficient experience in measuring such work 
in this country to decide whether Mr. Gallier's statement is cor- 
rect according to the custom of the country, or an error that has 
been overlooked. The dimensions are all right down to the vertical 
joints, which are expressed by 1 foot, multiplied by 6 inches, and 
the product repeated or multiplied 10 times, because the question 
states that there are 10 vertical joints. It will be observed in 
the preceding sum that the beds are repeated 8 times, although 
there are but 4 courses of stone, thus showing that the top and 
bottom of each course of stone is separately measured in plain 
work, and this, according to the English system, applies equally 
to vertical joints. If 10 such joints occur, they imply that 20 
surfaces or sides of stone have been rendered flat and smooth, and 
in addition to this if the extreme ends of the wall have been ren- 
dered flat and smooth, these ends would also count. Thus by 
referring to Fig. 168, it will be seen that the wall there repre- 
sented consists of four courses with 10 vertical joints, as in the ex- 
ample; but these 10 joints require 20 flat surfaces, in addition to 
which there are 8 flat ends to the courses, consequently, accord- 
ing to the English mode of computation, the co-efficient or multi- 
plying number for the area of one joint would be 28 instead of 
10, as stated in the example. If the Amerian custom is to call 
each vertical joint, one face of plain work only, it produces a 
considerable advantage to the employer. 

Sections. — Of Brick-work. 

902. The method of building with bricks is so nearly similar to 
that with stones that many of the remarks made in the last sec- 
tion will apply with equal propriety to both materials: and as 
this also appHes to some of the observations about to be made on 
brick-work, so the simple term wall will be employed, in future, 



484 OP BRICK-WORK. 

to denote erections that may be made indifferently of either ma- 
terial or operations that apply equally to them both, and brick- 
wall or stone-walU when either particular kind of work is referred 
to. The nature of bricks, and their dimensions and qualities have 
been already described (477 and 493,) and in using them for 
building purposes, an even surface or foundation is first prepared, 
and should be truly level in each direction.* This may be cover- 
ed with mortar, and the bricks are then placed upon it flatwise, 
or with their broadest surfaces upwards and downwards, with 
mortar filled in between their vertical joints; but the general 
practice in beginning a wall is to lay the first or foundation course 
dry, or without mortar; that done, another layer of bricks is 
placed above the first, each layer being called a course of brick- 
work. Any course being finished, mortar is laid over a part of 
its upper surface to bed the bricks of the next course, and in this 
manner the work proceeds upwards until finished. 

903. All bricks that are laid with their length in the direction 
of the length of the wall are called stretchers^ and all those that 
take an opposite direction, or present their ends towards the faces 
of the wall are called headers, whether they are visible on the 
outer faces of the wall or are hidden within it. 

904. A heading course is one in which all the bricks that com- 
pose it are headers; and a stretching course has all its bricks laid 
as stretchers. All brick-walls ought to commence with a head- 
ing course, in order that the lower bricks may be so covered by 
the superposed wall that they cannot slip out of their places. 

905. Brick-walls are generally described by the number of 
bricks that occur in their thickness, rather than by their dimen- 
sions in inches; thus we speak of a single brick-wall, a brick and 
half wall, two bricks, &c., and if the size of the bricks are deter- 
mined as they are in England, (476,) this at once gives the thick- 
ness of the wall, and then walls are spoken of as nine inch, four- 
teen inch, eighteen inch, &c. walls. A four inch wall is one that 
is half a brick thick, or built with whole bricks all laid in the 
direction of their length. In paving with bricks, or bringing up 
courses to a proper level, the bricks are often laid with their thin 
sides upwards, and when so disposed this is called brick on edge- 
work. Brick on end-^NOvk is only used for paving floors, and in 
this the bricks are placed with their ends upwards. From the 
small dimensions of bricks a great part of the strength of brick- 
work depends on the joints being well and regularly broken, or so 

* It may appear that some further observations on the nature of foundations 
should be made here, but they are of such vast importance to all buildings that a 
separate section will be devoted to their discussion, after the processes of build- 
ing have been described. 



OF BRICK-WOKK. 485 

disposed that no two vertical joints shall occur in the same line 
over each other in two contiguous courses; or in other words, 
that good bond should be preserved; and yet to make the work 
look handsome, all vertical joints in alternate courses must be cor- 
rectly over each other, so that if a long plumb-line should be 
fixed in any vertical joint of a piece of work at its top or upper 
course, that line should also cover or pass over the vertical joints 
in every alternate course below it. 

906. In order to produce this regularity of appearance in the 
joints, so necessary to the handsome appearance of brick-work, 
as well as to break the joints and cause the bricks to overlap 
each other for procuring strength, bricks are always laid in par- 
ticular forms distinguished by the name of Bonds, Of these two 
varieties are used in England, and are called Old English Bond 
and Flemish Bond, and a third variety has been introduced in the 
United States, where it is extensively used, and may, therefore, 
for distinction's sake, be called American Bond. 

907. Old English bond consists of alternate courses of all head- 
ers and all stretchers alternating with each other, except when 
the wall contains an odd number of half bricks, and then a single 
row of stretchers becomes necessary in each heading course, and 
a row of headers in each stretching course to make out the thick- 
ness of the wall. Thus, for example, in building a brick and half 
wall, or a two brick and half wall, such thickness can only be 
obtained as above, or by cutting whole bricks into halves, which 
would occupy more time, and produce great waste of material. 
The first course of a brick and half old English wall would there- 
fore be laid headers and stretchers, disposed as at A in Fig. 173, 
and the next higher course in succession would be like B, or show 
its stretchers on the opposite face of the wall. If the wall is 2j 
bricks thick as at C, the stretching course can be laid in the mid- 
dle of the wall, and then the succeeding course may be all 
stretchers. And when the wall is two bricks thick as at D, it may 
consist entirely of alternate courses of headers and stretchers. 
The forms C and D are, however, neither of them proper for 
building walls, because the joints are not sufficiently broken; for, 
as each of these courses has to be covered with a course of all 
stretchers, whose positions are shown by the dotted lines, it will 
be evident that a straight joint, or one without bond, will run 
through the whole length and height of each of these walls, and 
that there is nothing to tie the two faces together, consequently 
such walls would be liable to split in two in their vertical longi- 
tudinal direction when loaded, or carried to a considerable 
height. To obviate this, every third or fourth header should 
be laid in the middle of the wall, as at a a, when its deficient 



486 OF BRICK-WORK. 

length must be made out by pieces of brick called halts, or bricks 
cut to shorter lengths, as at 6 6 6 6, which will not at all alter the 
external appearance of the face of the wall, but will add mate- 
rially to its strength. In reference to the plans A and B, it will 
be seen that as the length of every brick should be equal to twice 
its breadth, so if whole bricks are wholly used in laying down A, 
the stretcher joint c will always come in a line with the header 
joint d, and thus produce bad work, or straight contiguous joints; 
to avoid which a portion of the first stretcher e must be cut off 
so as to reduce its length, until it is equal to the breadth of a 
brick and half, as in the figure, when each vertical joint c will 
come against the middle of the end of a whole brick, and the 
joints will be broken throughout the whole work. Pieces of brick 
less than half a brick in width are often necessary in the face of 
a wall to shift a joint, so as to produce good bond, and such short 
pieces are called closers, but pronounced closhures. E shows the 
appearance that old English bond has on the face of the wall. 
The advantage of this kind of bond is that it contains no hollows 
or interstices, but is perfectly solid, and is therefore peculiarly 
well suited to any work in which great strength, rather than 
beauty of appearance, is desirable. It is therefore constantly 
resorted to both in masonry and brick-work, for the piers and 
abutments of bridges, the side walls of canal locks, and all such 
purposes. 

908. Flemish bond has the external appearance shown in Fig. 
169, and consists of headers and stretchers alternately in every 
course, but so disposed that no vertical joints occur over each 
other in contiguous courses. This bond is generally adopted in 
house building, because it is thought to look handsomer, and takes 
fewer bricks, or at any rate permits the builder to use a great 
deal of the small batts and broken rubbish that constantly occur 
in building; for no wall, consisting of an odd number of half 
bricks, can be built solid when this bond is adopted. Fig 174, at 
F, shows the disposition of the bricks in a single brick wall, and 
G that of a two brick wall, both of which are solid, and consist of 
whole bricks; but H shows the disposition in a brick and half 
wall, in which many cavities//are inevitably left, and these are 
always filled up with mortar and small fragments of brick, which 
not unfrequently also happens in the wall G, where instead of in- 
troducing the two whole bricks g g, one only is often used, and 
the remainder filled in with rubbish, as at h. This is more par- 
ticularly likely to happen in work contracted for, and in which the 
contractor has to find all materials, as by this means many whole 
bricks are saved. 

909. The third variety of bond, which we have distinguished 



OF BRICK-WORK. 487 

by the name of American bond, is produced by laying four or five 
courses, one above another, all in stretchers, and then alternating 
with a single course of headers, followed by the same number as 
before of stretchers, as shown at I. This, like old English bond, 
produces solid work, but without the strength of the former, for 
the stretching courses must have straight vertical longitudinal 
joints between them, depending only on the single heading course 
to tie them together, and as it produces no beauty of appearance 
it cannot be recommended. ' 

910. Mr. Robert Vazie, a Cornish Engineer, some years ago 
endeavoured to introduce what he called vertical bond into wall 
building, and from the experiments he tried, it appeared to possess 
a decided advantage of strength in walls subject to lateral pres- 
sure, such as in supporting embankments of earth. Vertical bond 
is produced by working bricks on end into the middle of the wall 
at two or three feet apart. Some of these are placed on each 
succeeding course, so as to carry the perpendicular tye from the 
bottom to the top of the wall; and each vertical brick will of 
course be covered and hidden by three successive horizontal 
courses. In using this bond great care is necessary to see that 
the vertical bricks are not too long; for, should this be the case, 
they would prevent the due settling of the wall, and produce 
horizontal cracks and weakness rather than increased strength. 

9il. Straight walls are built by first setting out the quoins or 
angles of the building upon the ground, and then straining a line 
from one point to the other, which will of course be straight. The 
line is fastened at its two ends to what are called line-pins, which 
are stuck into the soft mortar joints. In order to be able to fix this 
line in its proper place, two quoins of the building must be carried 
up three or four courses higher than the intermediate work, and 
the lower courses must be made truly level by the application of 
the bricklayer's level (300). That done, the work may proceed 
upwards with any required rapidity, all that is necessary being to 
examine that the faces of the wall are truly perpendicular, which 
is done by the application of the ed^e of a plumb-rule at every 
course, and an occasional examination of the level state of the 
courses, which ought to be made at every 5th or 6th course. The 
plumb-rule should be at least 3 feet long, and instead of holding 
it on to the last finished course, as is sometimes done, it ought to be 
made to bear about 18 inches against the finished wall below, to 
obtain the surest indication. 

912. To insure the stability of a high wall that has nothing to 
support it, it is quite necessary that it should be perpendicular, or 
at any rate that its centre of gravity should be completely within 
the base or foundation upon which it stands; and upon the princi- 



488 OP BRICK-WORK. 

pies before explained, (837, et infra,) a wall to be equally strong 
from bottom to top, ought to be thicker near its base than near 
its top, and this is always attended to in building high walls. 
Thus, for example, in a three story house, the external walls may 
be 2 bricks thick up to the parlour ceiling at a, Fig. 175, and 
there a break, or set-off, of 4 inches may be made, so as to reduce 
the thickness of the next walls to \^ bricks. In the ceiling of the 
next room at h, another set-off of 4 inches more occurs, reducing 
the thickness of the last story to a single brick wall; thus lighten- 
ing the load and diminishing the expense as the building proceeds, 
without diminishing its actual strength. In addition to this it is 
always customary to give a wider base to a wall than its thick- 
ness, and this called the footi?ig of the wall. Thus the 2 brick 
wall may begin with a 4 brick footing, as shown in the Fig., 
and this footing diminishes by small breaks, or sets-off, at every 
second or third course, until it reaches the thickness the wall has 
to have above ground; for the footings of walls are, in general, 
under ground, and therefore invisible. This explains what has 
been before stated, (904,) that every wall should commence with 
a heading course, as an external line of stretchers might slip out 
of their places for want of being covered by other bricks. 

913. In order to give the greatest possible stability to a wall, it 
ought to stand over the middle of its footing, as at c/, Fig. 175, and 
the offsets ought to be equal on both sides of the wall. This is 
however impossible in practice, since it would give a building a very 
bad appearance, if its principal front was crossed by the projec- 
tions that such offsets would make, and they would moreover be 
detrimental, by catching and retaining water. The face of the 
external wall is therefore necessarily made flat like c, and the off- 
sets a and b are confined to the inside, where they are hidden, by 
becoming the ledges that support the joists of the floors, at which 
places the offsets should be made; but this throws more of the 
weight of the wall to the outside than to the inside. In houses for 
containing steam-engines, warehouses for heavy loads, and manu- 
factories requiring buildings of more than ordinary strength, this 
may be remedied without producing any disagreeable appearance, 
by introducing a string course of stone, weathered on its top, 
wherever an offset may be desirable in the external wall, which 
may be set back an inch and a half or two inches above such string- 
ing, without producing any disagreeable appearance. 

914. It sometimes happens that a wall cannot be set upon the 
middle of its footing without the loss of a small portion of ground; 
for the divisions of land and estates run in planes from the surface 
to the centre of the earth, and no man has a right to build, dig, 
or perform any act that may infringe on the rights of his neigh- 



OF BRICK-WORK. 489 

bour. If, therefore, we desire to build the front/ c on the utmost 
limits of any estate, it must be without any projecting footing be- 
yond the dotted line c, which is the extreme boundary. The 
wall, therefore, must be without any foot next the side c, or else 
the whole footing must be moved so far inwards upon the estate, 
that its extreme edge may be in the boundary line, instead of the 
perpendicular fc, which will thus be thrown back by a distance 
equal to the projection of the footing. 

915. When walls are required of extraordinary strength, as to 
withstand high winds, or the pressure of embankments of earth 
made against one side of them, they are made to slope, or batter, 
as it is called, that is, they are made much thicker at the base 
than at the top; or if they are built vertically they are assisted 
and strengthened by buttresses, or counter -forts, placed at shorty 
but sufficient distances from each other, to produce the necessary 
strength. When walls are built in this form the horizontal position 
of their foundation is still preserved as to its length, but it ought 
not to be level in the transverse or opposite direction; because as 
bricks and stones are generally used in parallel horizontal courses, 
a transverse level foundation would not produce the greatest 
strength, and yet would be attended with increased labour in its 
formation. Thus let abed, Fig. 176, be a transverse section of 
such a battered brick wall, built to resist the lateral spreading 
force of an embankment of earth e. If the bottom course c d is 
level, all those above it will be parallel to it, or all the wall will 
consist of horizontal courses, while its exterior battered face a c 
will be a series of small steps or offsets, unless each course of bricks 
in succession is cut in the direction of the dotted line a c, which re- 
quires much additional workmanship, and after all, will never pro- 
duce the appearance of an even and well finished face to the work; 
nor can such a wall offer the gjreatest resistance to the bank of 
earth e, the lateral spread or thrust of which will be in the hori- 
zontal direction of the arrow under e, and as it is opposed by 
nothing but flat horizontal joints and courses of brick-work, 
diminishing rapidly in weight as they proceed upwards, and hav- 
ing no bond among themselves, (unless vertical bond (910) has 
been introduced,) there will be great probability of the upper part 
of the wall being pushed or made to slide horizontally out of its 
proper place, or at any rate cracking and losing a part of its 
strength and stabihty. If, on the contrary, we draw a line ef 
from e, the centre of gravity or central height of the soil bank to 
be supported, and carry its lower end/ to about the middle, or 
near to the outside of the bottom of the intended battering wall, 
another line eg may be produced at right angles to the first, and 
this will give the direction in which the courses of brick-work 
62 



490 OP BRICK-WORK, 

should incline to produce the greatest effect of strength; instead, 
therefore, of building the wall as shown in Fig, 176, the bricks 
should be disposed as in Fig. 177, when the only cutting to be per- 
formed will be in the vertical plane AA:,which being within the wall, 
its imperfections, if any, will not be seen, while h i will present a 
smooth and finished surface of entire bricks, and all the courses 
heing parallel to the foundation ik, will oppose the most effectual 
resistance that can be obtained against the lateral pressure. 

916. Except for supporting the embankments of canals and re- 
servoirs, walls seldom batter to such an extent as in the example 
just given, but they are often required to batter in a slight degree, 
such as from Jan inch to 2 inches in a yard perpendicular, to give 
greater strength to the works of the Engineer; and in such slight 
cases, no slope is necessary in the foundation, nor should the facing 
bricks be cut except when absolutely necessary, because this de- 
gree of batter can always be obtained by making the mortar joint 
wider on the face of the wall than in its inside. In fact the inter- 
nal bricks may be laid close, or with scarcely any mortar between 
them in the middle of the wall, and then a joint of ordinary size 
will suffice for the outsides. 

Battering walls are always built by a battering plumb-rule, that 
is, one in which the sides are cut to the necessary batter, instead 
of being truly parallel to the central line over which the plumbet 
hangs. Such a plumb-rule is on the principle of that before 
described, (371,) and shown by Fig. 105, for setting out and proving 
the slopes of canal banks. 

917. As walls that batter considerably are always expensive 
on account of the great quantity of materials they consume near 
their bases, buttresses or counter-forts are very commonly used with 
a common straight wall, instead of a long battering wall, and, in 
many instances, with equal effect. Thus the side walls of canal 
locks are usually in this form. The ground plan of a wall with 
buttresses is shown at Fig. 178, PL VI., in which /m is the straight 
face of the wall, and nnn buttresses formed against its opposite 
side; and these in lock walls are placed on their land sides, at 4 
or 6 feet apart, according to the depth of the lock. To produce 
more strength in the walls they might batter, and be built in 
either of the forms shown at Figs, 176 or 177, but as such walls 
are not only subject to the lateral pressure of the water and earth 
on their two sides, but to concussions near their tops from loaded 
boats when the locks are full of water, they are usually carried 
up perpendicularly to near the ground level, and when that is the 
case they will work better in level, instead of sloping courses. In 
the old Gothic buildings of Europe, which are usually very high, 
buttresses are constantly used, one being placed between every 



OF BRICK-WORK. 491 

window, and at their bottoms they frequently extend out a great 
distance, and are diminished in their extent as they proceed up- 
wards by sloping offsets, as shown at q, Fig. 179, and they finish at 
their tops in slender pyramids r called pinnacles, which being fre- 
quently enriched, add much to the beauty of Gothic buildings. 
In many instances instead of terminating in a mere pinnacle, they 
carry a quarter of a circle of stone arched work, as at p in the 
figure, when this arch, from its apparent want of support, is called 
a flying builress. It is not however deficient in support, and its 
real use is to transfer a part of the strength and resistance of the 
m^in buttress q, to points ss where resistance was necessary in the 
roofs used in these buildings, as will appear in the next section, 
when treating of the construction of roofs. 

918. In the same way that buttresses are used to save materials, 
and yet produce strength in heavy work, so likewise pannels are 
frequently introduced into the brick-work of ordinary walls, by 
which their appearance is much improved, particularly if the ne- 
cessary wall is high, and is a dead wall, (this being a term that is 
applied to walls having no doors, windows, or other openings 
through them.) Thus instead of carrying up the side of a house 
or other building as one uniform flat surface, its appearance will 
be much improved if it is built as shown at Fig. 180. That is, 
commencing below with a plinth of ashlar facing or brick-work, 
of 2 or 3 feet in height, up to the line s s, where the wall should 
set back or show a break of 2 inches. The wall t then goes up 
for 6 or 8 courses in a perfectly flat manner until the pannels u u 
commence, and the faces of these may be set back two inches 
more, or even half a brick, if the pannels are large. The work 
proceeds upwards until the height of the pannels is completed, and 
then the wall a; breaks forward again so as to become flush or even 
with the face of v v, leaving a break of equal depth round the four 
sides of each pannel, and the whole may be surmounted by a cor- 
nice y. This design is taken from the street front of the Cannon 
brewhouse at Knightsbridge, near London. The pannels extend 
laterally much further than in the figure, and the whole has a 
very bold and handsome appearance. The advantage of this mode 
of building, independent of its appearance, is that by setting the 
wall 2 inches back upon the line 5 5-, and 4 inches in the pannels, the 
centre of gravity is thrown further back, so as to be over the mid- 
dle of the footing; and 4 inches in thickness of brick-work is saved 
over the whole surface of the pannels, which in a large building 
is considerable, while the projecting piers vv produce strength 
nearly equal to that which would have been obtained had the 
wall been of uniform thickness. If it should be desirable to in- 
crease the elegance of appearance, white free-stone mouldings in 



492 OF BRICK-WORK. 

the form of capitals, may be introduced over every projecting 
pier, as at w, so as to give them the appearance of pilasters. 

The same mode of construction may be adopted with equal ad- 
vantage in house building. Thus Fig. 181, is the end elevation 
of the engine house of the West Middlesex Water Works, at 
Hammersmith, near London, erected by the writer in 1810. It 
contains two 70 horse power steam-engines, with their pumps and 
apparatus for supplying water from the river Thames to the 
Metropolis of London, and therefore requires great strength. The 
construction is the same as that last described, except that the 
sunk pannels commence at the top of the plinth, and terminate 
above in semicircular arches, instead of straight lines, the arches 
springing from a stone string course, constituting imposts in this 
case, because the stringing merely passes over the piers, and is not 
continued through the pannels. 

919. As bricks are right angled at all their edges, of course 
they are better suited for building straight than curved walls, nor 
can they be used for any quoins or angles, except right angles, 
without cutting them. It frequently happens that buildings and 
walls require other angles, and whenever a wall deviates from its 
right lined direction to a less extent than 90°, such wall is said to 
splay, and the bricks at the external angle of the splay must be 
cut to suit it. Thus, suppose two walls are required in the direc- 
tions a and b of the ground plan, Fig. 182. Those walls can only 
be built of common bricks with right angles at their ends, and in 
order to produce bond in the angle, each wall must over-sail or in- 
tersect the other, as shown in the figure, the consequence of which 
is that a triangular portion c d o( every brick will project beyond 
the face of the wall, appearing alternately on each side of the 
perpendicular line which forms the point of the angle; and it is 
these triangular portions that require to be cut away by the edge 
of the trowel from each brick as it is laid at the angle, which is 
called cutting to splays; and being attended with extra trouble and 
workmanship, this cutting is always allowed for in measuring the 
work, and is charged by lineal measure, or at an agreed price per 
foot run upon the height to which it extends. 

920. In like manner, a similar extra allowance is always made 
for cutting to rakes and ramps. A wall is said to ramp when in- 
stead of terminating in perpendicular ends it assumes the form of 
a vertical angle, as in the gable end of every house, or in lean-to 
buildings, or such as are built against the side of another building. 
Thus, if it was proposed to close up the end of the building. Fig. 
179, by a wall, it would proceed vertically at both ends, in the 
principal building A until it reached the points .95, and then it 
would take angular directions to t, in order to fill up the trian- 



OP BRICK-WORK. 493 

giilar space s t s, while in the lean-to building B the wall would 
terminate in a sloping direction correspondent with the roof v. 
Such walls would be said to ramp at v and from s to i, and to pro- 
duce such ramps every brick requires to be cut, otherwise the wall 
would show a series of indentations like ac, in Fig. 176. The 
rake is the quantity of angular deviation from a horizontal line, 
thus we say that the ramp of a wall rakes 2 to 1, as in canal 
banks (358), or a ramp may have a rake or slope of 22°, or any 
other number of degrees. Ramps are sometimes curved instead 
of right lined, of which the wing wall w, in Fig. 181, is an ex- 
ample. 

921. When walls are built circular, or curved on the plan, it is 
evident they cannot be carried up by the line and pins, which can 
only give right lines. Curved work must therefore be carried on 
by what are called moulds, and these are merely thin boards 3 or 
4 feet long, one edge of which is cut into the curved form the wall 
is intended to have; and they are used in the manner of a ruler, 
being applied upon the upper surface of every course of work at 
the commencement, when the bricks or stones are placed in exact 
coincidence with the curved edge. When the first two or three 
courses are laid, the mould will only need occasional application, if 
the wall is to be perpendicular, because the plumb-rule, used in the 
ordinary way, will be sufficient to carry the work up correctly 
from the bottom courses, if properly laid. When curved work is of 
small radius, it will require all whole bricks to be cut into wedge 
shapes, or must be worked with half bricks; and as it is in every 
case more slow and troublesome than plain work, it is customary 
in London to allow one-third more money for its execution than 
for plain work. The perpendicular offsets that occur round win- 
dows, or in forming pannel w^ork, as in Fig. 180 and 181, are call- 
ed reveals, and as they are more troublesome than a plain wall, 
they are subject to a small extra charge upon their lineal mea- 
sure, unless an agreement is made to the contrary. The bedding 
of wall plates, and fixing door and window frames in a wall, is also 
an extra charge. 

922. It sometimes happens that the bricklayer may have to wait 
for the carpenter or joiner, on account of his not having timbers, 
or door or window frames ready for fixing at the moment they are 
required; and in such cases, rather than be delayed, the brick- 
layer will rack back his work, that is, carry it up at the quoins, 
or such parts as require nothing to be inserted in them, as shown 
at Fig. 183, and leave it low in other parts, still however working 
back in steps, so that the deficient vi'ork may be added afterwards 
without any variation of the bond and external appearance of the 
wall. Racking back is often inevitable, and is not detrimental 



494 OP BRICK-WORK. 

unless when carried to too great an extent, which ought to be 
carefully avoided, especially in brick-work: for in that, the sum of 
the heights of the horizontal mortar joints form a much larger 
proportion of the entire height of the building than in masonry. 
Now as mortar is soft when first used, and the bricks become a 
heavy load as the wall ascends, the mortar of the lower joints 
will, of course, be somewhat compressed, and the wall must sink 
or settle until the mortar becomes hard, when no further change 
can occur in its height. When racking back is carried up a con- 
siderable height, such setting will, of course, take place in it, and 
if left a few davs, the mortar used will have become hard. The 
work that is afterwards filled into the cavity will also have to set- 
tle, consequently its joints must be made rather thicker than those 
of the old work, or if not, the new work will sink in its horizontal 
joints below those of the old work, thereby breaking the vertical 
joints, and spoiling the appearance of the whole, and not unfre- 
quently producing cracks that are detrimental to its strength. 

923. As a general rule, therefore, the brick-work or masonry of 
every large building ought to be carried up as nearly as possible 
of one uniform height all round, which is easily effected by having 
workmen stationed on every side who work simultaneously; or, 
when hands are scarce, the slower process of working the same 
level course, or nearly so, all round the building should be adopted, 
and no one part be permitted to rise more than a foot above the 
others, by which means an equal weight will be thrown upon 
every portion of the foundation and lower work, and no one part 
will have a greater tendency to sink or settle than another. 

924. In the immense city of London where nearly every thing 
is built with bricks, and consequently the workmen have the best 
experience of what is good or bad in its execution, this circum- 
stance of keeping the courses of even height, and distributing the 
load as evenly as possible over all the substructure, is so closely 
attended to, that even a common house is never built without 
running strings of bond timber around the whole building, and re- 
peating them at about every 4 or 5 feet in height. Bond timber 
is merely pitch-pine or oak scantling of 4J by 2f inches square, or 
the same size as the end of a brick, in long lengths, and it is laid 
upon the walls in a level position, sometimes in the middle of the 
wall, but more frequently flush with its inner face, and lapped 
and nailed at all angles, or wherever joints occur in the wood, and 
being bedded in mortar, and built upon, it becomes a permanent 
part of the wall, and not only transfers all the load of the upper 
structure to that below, but prevents unequal settling and the pos- 
sibility of vertical fissures taking place in the wall. As the whole 
front of a house is frequently run up so rapidly, that the mortar 



OF BRICK-WORK. 495 

in the base has not had time to set and become hard before the 
top is finished, such walls would be very apt to warp or wind, that 
is, to loose their perfectly flat vertical surface by some parts bulg- 
ing outwards and others sinking in, was it not for the bond timber, 
which effectually prevents this occurrence; for although the bond 
timber is not strong, yet a very little force or restraint will be 
sufficient to maintain the flat figure of a wall, if it has been well 
built, and has been kept truly perpendicular during its erection. 
The more effectually to secure this object, bond timber is always 
permitted to run across all doors, windows, or other openings with- 
out any intermission, and it is sawed out of these openings when 
the work has become hard and dry, and has settled to its full ex- 
tent, so as to make the continuity of the timber no longer a matter 
of importance. All joists, and beams also, rest upon the bond tim- 
ber, which thus becomes a template (884), for distributing their 
weight over a large under surface. In Fig. 175, a, b,g g g, show 
sections of the bond timbers as introduced into all houses in Lon- 
don. 

925. For the same reasons that racking back is detrimental to 
the appearance and strength of work, so likewise the method of 
uniting new work to old by means of what is called toothing is, if 
any thing, worse, notwithstanding it is much used. Toothing de- 
rives its name from the regular tooth-like appearance of the joint 
before it is made, as shown at e, Fig. 184, and it is frequently seen 
running up the whole side of a building to which it is contem- 
plated to join another at some future time. If the walls proposed 
to be added are to be at right angles with the old wall, then the 
toothing is produced by leaving out a brick in every alternate 
course, in a vertical line, as shown at/. The new wall, in both 
cases, must be built with bricks so projecting as to fit into these 
indentations, but such new work will be almost sure to crack in 
settling, owing to the bricks in the toothing being upheld, or not 
permitted to descend and settle with the rest of the work. The 
modern improved method of producing a junction, or tying of new 
work to old, is by leaving what is called a chase in the side of the 
old work, as shown by the dotted lines at g, and the new work 
when built is formed with tongues, as at h, which fit into the 
chases, thus holding the two walls together, and producing the 
appearance of a perfectly straight vertical joint between the two 
buildings,' and permitting the new work to sink by sliding down- 
wards against the old work, to admit which, care must be taken 
at the time of building that the bottom of every tongue shall be 
at least one, or if the wall is high, two courses above the bottom 
of the chase into which it fits. The chase is left from ^ a brick 
to a whole brick behind the face of the wall, not only to insure 

63 



496 OF BRICK-WORK. 

strength, but to conceal the mode of joining and produce the ap- 
pearance of a straight joint, i Shows an indent left for a wall to 
be built at right angles to the first. 

926. A low wall can be built for less money than a high one, 
because in the former, the materials are easily conveyed to it; no 
scaflfblding is necessary for carrying on the work, and there is 
none of that loss of time and labour, constantly attendant on rais- 
ing heavy materials to a great height. Whenever the height be- 
comes such that the workman cannot reach his work, (and which 
should always be beneath his chin,) scalTolding becomes necessary, 
and this is usually constructed by fixing long poles in upright posi- 
tions about eight feet apart and six feet in front of the wall to be 
erected, these are crossed and braced together by horizontal poles, 
tied on to the upright ones, wherever a stage may be necessary, 
and shorter poles, called putlocks, are placed at four or five feet 
asunder, one end resting upon the horizontal poles and the other 
passing into J brick holes purposely left for them in the wall, 
and called putlock holes. The putlocks are finally covered with 
1^ inch boards, which form the floors or platforms of the scaffold, 
and these boards and putlocks require neither nails, tying, or any 
kind of fixing, as they are sufficiently firm and steady from their 
own weight, or the loads placed upon them; but all the materials 
have to be delivered on to these platforms, and this constitutes a 
considerable item of expense in very high buildings. Heavy 
stones, pieces of timber, and articles that are too heavy to be car- 
ried up a ladder by a single man, are usually raised by shear 
poles, such as have been already explained, (884,) or by blocks 
and a fall attached above to a strong projecting pole, fixed for the 
purpose near the top of the scaffolding. But bricks, mortar, and 
the more portable articles are carried up by tall ladders, or occa- 
sionally, in this country, upon inclined planes, formed by a suc- 
cession of sloping scaffold boards, rising first in one direction and 
then in another, and these have been preferred, on the principle, 
that a man can carry a greater load up a gradual slope than up 
an almost perpendicular ladder. This is, no doubt, true, but at 
the same time, to make the inclined plane easy of ascent, its surface 
must be made so much longer than the ladder, that a man moving 
with equal speed might ascend the ladder twice, while he would 
move once up the inclined plane; consequently, if he could only 
carry half the weight at once up the ladder, he would deliver fche 
same weight of load in the same time, whether he ascended by 
one means or the other. In England the ladder is constantly used, 
and the bricks, tiles, mortar, &c. are carried up on the shoulder 
of a labourer in an implement called a hod, which is found very 
convenient for the purpose. The hod is formed of two strong 



OF BRICK-WORK. 497 

boards nailed together at right angles to each other, with a square 
board to form an end, so that it is a trough of three sides, the top 
and one end being open. Its inside dimensions are nine inches 
wide on each board and sixteen inches long, so that it will hold 
eighteen bricks, or very nearly half a bushel of mortar. A wooden 
shaft or handle, three feet in length, is attached by a hollow socket 
of iron, terminating in a fork like a Y, to the centre of the angu- 
lar bottom, which being rounded and covered with a pad of car- 
petting, the load is easily carried on the shoulder, and by placing 
the handle in a slightly incHning direction over the front of the 
body, a man will with some practice carry a loaded hod with 
great speed up a ladder without holding it at all; consequently he 
has both his hands at liberty for his security, or to assist him in 
climbing. High building ladders ought to be strong enough to bear 
the weight of three or four loaded men upon them at once, be- 
cause when buildings proceed rapidly, the ladder is generally 
filled with labourers following each other in rapid succession. 

927. By experiments that have been tried, it has been found 
that few men, even among those who are in the constant habit of 
serving bricklayers, can work under a load equal to half their own 
weight, for a whole day, which in England is made up of ten 
hours actual work. That is to say, twelve hours are considered a 
day; but half an hour is allowed for breakfast, one hour for din- 
ner, and half an hour at 4 o'clock for rest or refreshment. Taking 
the average weight of men at I20lbs. it is found that 45lbs. is about 
the average load they can carry constantly, therefore, in the 
raising of materials for extensive buildings, a great advantage 
arises from using the weight, instead of the strength of men. This 
method was adopted in the building of the present Drury Lane 
Theatre, in London, which is a very lofty and extensive building. 
Instead of carrying up the smaller materials by ladders as usual, 
large cast iron single pullies of about four feet in diameter, with 
deep grooves on their edges, for ropes to run in, were fixed in the 
scaffolding, at a height somewhat above the greatest intended 
height of the building. A single rope being passed over each pul- 
ley had two large, strong, square boxes, one attached to each of 
its ends, and the rope was so adjusted as to length, that when one 
box rested on the ground, the other was elevated to a few inches 
above the height of that stage of the scaffold on which the mate- 
rials were to be delivered. The lower box being filled upon the 
ground with bricks, mortar, water, slates, or any materials required, 
a man stepped from the scaffold into the upper box, and the load 
below was so adjusted as to be ten or twelve pounds lighter than 
himself; consequently he would descend, holding by the rope, with 
a velocity due to the difference in weight of the two loads, but 
63 



498 OP BKICK-WORK, 

had the power of diminishing this velocity by letting the ascend- 
ing rope slide through one of his hands as he descended, or by 
holding it tight, could even stop all motion. By this method the 
labourers could raise loads that were very nearly equivalent to 
their own full weight, and with scarcely any fatigue; the only ex- 
ertion of strength being during their ascent of the ladders, which 
they had to run to and climb up as soon as they were landed on 
the ground, and the upper loaded box was hauled on to the scaf- 
fold to discharge its contents. But they had to ascend empty 
handed instead of being fully loaded, and could therefore move 
with much greater speed, and the advantage in economy of labour 
and expense was enormous. This method of raising materials was 
probably taken from a process of a similar character that has 
been used during many years for unloading the coals that are 
brought in the holds of vessels into London. A very large basket 
being slung from the end of a rope is lowered into the hold of the 
ship, the other end of this rope being passed over an elevated 
sheve or pulley, terminates in four separate ropes about five feet 
above the deck of the vessel; a man holds on to each of these, and 
when the basket is filled, the four men jump simultaneously down 
the hatchway, and by their joint weights overcome the weight of 
the coals, which are thus raised as high as the deck, and there 
they are caught and swung to one side by two other men standing 
in readiness to receive and discharge them, by a wide trough or 
shoot over the side of the ship into a lighter moored to receive 
them. The empty basket is then thrown down to be refilled, and 
the time occupied in its filling allows the four men ample time to 
ascend again to the deck by a ladder, and prepare themselves for 
another jump. The distance passed through in unloading coals is 
very insignificant when compared with that of a high building; 
and it may, therefore, appear that the lives of the labourers are 
placed in great jeopardy by using the Drury Lane method of rais- 
ing materials, and it was accordingly much reprobated when first 
introduced, from a just notion that no saving of time or expense 
to the builder ought to be adopted if it exposed the lives of fellow 
creatures to a more than ordinary risk. The danger is, however, 
more ideal than real; for sailors, who are in the habit of living 
among ropes, and are frequently suspended by them, and miners, 
who are daily accustomed to ascending and descending shafts much 
deeper than most buildings are high, feel just as much confidence 
in their personal safety, while suspended to a rope, as other per- 
sons unaccustomed to such support would feel upon the boards of 
a scaffolding, or any other apparently more substantial support. 
And those who know how careless labourers (who are accus- 
tomed to the business) become, in ascending high ladders with 



OF BRICK-WORK. 499 

heavy loads, will admit that there is quite as little danger attend- 
ant upon descending by a good rope. At any rate no accident 
occurred to bring the method into disrepute while it was exten- 
sively and constantly used in the erection of this large theatre, 
and the labourers, when they became accustomed to it, preferred 
it to the ordinary mode of using ladders. A notice of it has been 
introduced here, from a conviction that the Engineer may employ 
the weight of workmen in raising loads, in many instances, with 
greater effect and satisfaction to the men, than if he employed 
their strength alone, as usually done. 

928. In the execution of brick-work, since a great proportion 
of the strength of the work depends upon a proper adhesion of the 
mortar to the bricks, it ought always to be used in a thin, rather 
than a nearly solid state, and in dry weather it will be advan- 
tageous to wet the bed, or top of the course to be worked upon, 
by sprinkling water from a large brush upon it, or even dipping 
the bricks into water. As the mortar is a more perishable material 
than the bricks, the mortar joints cannot be too thin, provided the 
bed is entirely covered with it. When it is necessary to give brick 
walls the greatest possible strength and solidity, and they are suffi- 
ciently thick and large to admit of the process, they ought to be 
grouted at every second or third course. Grouting is pouring very 
thin mortar, or common mortar mixed with as much water as will 
render it nearly as fluid as cream, upon the top of a course of 
brick-work, in order that it may run down between the joints and 
fill every hole and crevice that may have been left in the work. 
Whenever grouting has to be performed the surrounding edges of 
that course on which it is to take place must be carried up at 
least one course higher than the central work, to form a basin or 
recess for holding the grout, which should be stirred about with 
the edge of the trowel, or a small hoe, to distribute it evenly over 
the whole surface of the work. 

929. Nearly allied to grout in its nature, is the concrete, beton, 
or grubb-stone mortar, before spoken of under the head of ce- 
ments (528). As was then observed, this composition is little 
known in England, and the writer has never known an instance 
of its application or recommendation by any practical Engineer. 
As, however, it is spoken of in high terms of approbation by some 
of the French Engineers, and is said to combine many advantages 
for constructions in water and forming foundations, it ought not to 
pass without notice. 

Sganzin states that "grubb-stone mortar is used for building the 
foundations of hydraulic works; it is poured into the water, either 
directly, or by means of boxes made for this purpose, in order to 
prevent the mortar from spreading in passing through the fluid to 



500 OF BRICK-WORK. 

the bottom. No general rule can be given for the composition of 
grubb-stone mortar, as the quality of the materials influences the 
proportions and causes them to vary. The following is a compo- 
sition of this mortar, which has been employed with success: — 

Puzzolana from Italy, - - 12 

In 40 parts, <J Coarse gravel, - - - - 6 

Hydraulic lime, (quick,) - - 10 

Clippings of stone, - - - 12 

40 

**To make grubb-stone mortar, the puzzolana is spread and 
formed into a hollow basin, in which the lime is placed and slaked, 
according to M. Fleuret, after which the gravel is mixed with the 
lime and puzzolana; after the mortar is made, the clippings of 
stone are added without water, that used for slaking being sufli- 
cient. The mixture should be well worked with a hoe and shovel, 
after which it should be left for ten or twelve hours, and then be 
worked up again and mixed before it is used. When this mortar 
is required to fill up between two walls, to render the work im- 
permeable to water, the quantity of stone is reduced to one half, 
and to smaller dimensions; the gravel is also suppressed, and pit 
sand substituted." 

As the writer is unacquainted with the use of this mortar, it is 
perhaps not correct to hazard an opinion upon it; but it does ap- 
pear to him to be a wasteful process of employing expensive ma- 
terials, and one not calculated to produce the necessary solidity. 
He, therefore, prefers another process, which his experience has 
proved to answer the purpose of filling in or forming foundations, 
and that is to use broken stone free from round pebbles, and the 
harder the better; to place this in shallow layers not exceeding 
three or four inches thick — to beat down the stones into as com- 
pact a state as possible by a stone axe or light wooden hammer, 
and then to grout over the whole in the usual manner, except 
that the grout may be formed of cement or hydraulic lime, or of 
a mixture of common mortar grout with cement added to it, at 
the moment of stirring it into the work. This produces a very 
hard mass with a small quantity of expensive cement. 

930. As frosty weather is decidedly inimical to brick-work, be- 
cause mortar that is frozen will never afterwards set hard, but will 
always be pulverulent, no brick-work should ever be attempted in 
weather that is so cold as to freeze the mortar. And should frost 
come on after brick-work is finished, but before the mortar has 
had sufiicient time to set and get hard, the walls should be pro- 



OP BRICK-WORK. 501 

tected by thatching, or covering them with straw matting, or 
some protecting substance. 

931. Mortar joints should be finished on the face of all good 
walls, by passing the point of the trowel over them to render 
them quite smooth, when they are said to he fiat, and the work is 
CciWed fiat jointed. Formerly a practice existed of striking the joints 
of the best exterior work, which is nothing more than applying a 
straight edge or ruler to the middle of the joint, and drawing a 
flat, but round ended steel tool, so as to draw or rule an indenta- 
tion of about l^th of an inch wide, and half as deep, along the 
middle of the mortar joints. This must of course be done before 
the mortar sets hard, and gives a very neat appearance to the 
work when closely examined, but as it affords no advantage to 
brick-work when seen from a distance, and adds to its expense, it 
is now seldom adopted. Another method of ornamenting brick- 
work is by what is called tuck pointing, but this is generally em- 
ployed to renovate and beautify old work. The common mortar 
being raked out, is replaced, or pointed in with pointing mortar, 
made of common mortar mixed with powdered charcoal or soot, 
and the scoria from a blacksmith's forge. The joints are filled in 

fiat with this composition, which dries of a dark gray, or nearly 
black colour. A tuck or strip of fine stuff, made of finely sifted 
slaked lime and plaster of Paris, but no sand, mixed as thick as 
glazier's putty, cut by a long knife or trowel, so as not to exceed 
a quarter of an inch in width, is now laid carefully along the cen- 
tre of every joint, and if well done, it gives the work a very hand- 
some appearance. Tuck pointing is however tedious, and re- 
quires great accuracy of workmanship to look well, and is therefore 
expensive. 

932. Brick-work to furnaces, such as those for melting or re- 
fining metals, the boilers of steam-engines, the coppers of brewers, 
distillers, and the like, should be built with an internal facing next 
the fire, of fire bricks (495) at least half a brick, or frequently a 
whole brick thick, according to the constancy and intensity of the 
fire to be maintained; but the external walls may be of ordinary 
bricks. In fire- work, or brick- work exposed to the action of strong 
fires, the joints cannot be too thin, and no mortar should be used 
in them, for that would burn to quick lime again and loose all its 
tenacity. Instead of mortar, loam or fire clay, (if procurable,) 
tempered with water till rather thin, should be used, as this will 
burn hard by use: and as strong heat usually expands, vitrifies, 
and cracks the brick-work of furnaces, their sides ought to be tied 
or connected together by bars of wrought iron passing through 
the brick-work, and through cast iron plates on the outsidcs of 
the same, held by screws on the ends of the ties, or by iron keys 



502 OP BRICK-WORK. 

passing through them. The ties should, of course, pass in direc- 
tions where they will be as much protected from the heat of the 
furnace as possible. The flue or stack of all furnaces ought to 
have a separate foundation, and should in no case be set upon the 
furnace; for all furnaces wear out speedily, and require taking 
down and rebuilding, therefore the means of doing this without 
disturbing the stack should always be provided for. 

933. As Engineers, in the prosecution of their works, have fre- 
quent occasion for temporary buildings, both as dwellings and for 
workshops and storehouses, these are generally made of timber 
constructed as rough framed buildings, so put together that they 
can be taken down and removed from one place to another. But 
sawed timber is often scarce, and if the buildings are required for 
smiths' shops, melting metals, cooking, and other purposes where 
fire is extensively used, wooden buildings are not safe, and are ex- 
cessively hot in hot countries and seasons. It may not, therefore, 
be amiss to remark, that more comfortable and safe buildings may 
be easily constructed in hot countries where clay abounds, with- 
out burning it into bricks. The clay may be tempered with wa- 
ter and mixed with straw, to give it tenacity, when it may be 
moulded into large flat bricks, 24 inches long, 12 wide, and 4 
inches thick, which being set on their edges in the sun, and turn- 
ed, will soon have sufficient strength to be moved and used: and 
with blocks of such dimensions, the external walls of a single story 
house or workshop, with its fire-place, door, windows, &c. may be 
soon built, without any other mortar than the same clay rendered 
thin by water. The roof is formed by placing straight poles in a 
sloping direction, and covering them with the same blocks, thatch- 
ed on the outside with large leaves, slabs, shingles, or any thing 
that will protect the upper surface from rain; and all unnecessary 
chinks and holes being stopped and plastered with clay, a very 
comfortable dwelling as to temperature, either in hot or cold 
weather, will be produced. These sun-dried blocks of clay are 
called Adohis in Mexico, and a large proportion of the houses, out 
of the cities, throughout that republic, are built of no other mate- 
rial, and when plastered with lime plaster, they stand a number 
of years. 

934. Another mode of mud building, called pise hiiilding, much 
used in Italy and the south of France for farming purposes, is car- 
ried on by driving a double row of parallel upright stakes into the 
ground in the form of the intended building, the rows being at a 
distance asunder equal to the thickness of the proposed walls. 
Thin smooth boards are then set upright against the insides of the 
rows of stakes, and the space between them is filled up with tem- 
pered clay and straw, placed in even horizontal layers, and ram- 



OF BRICK-WORK. 503 

med down by wooden rammers. When this work becomes suffi- 
ciently dry to stand and maintain its shape, the boards are with- 
drawn, and placed in higher positions, to be again filled with tem- 
pered clay, and so on until the walls reach their full height. Bond 
timbers (924) may be placed at the bottom and top of each win- 
dow, and these, by running quite round the building, will add 
much to its strength and durability. Sir John Sinclair, in his 
Agricultural Reports, speaks in terms of approbation of these 
buildings, and recommends their use in England. 

Of the Measurement and Valuation of Brich-worh, 

935. Brick-work is almost constantly measured by the square 
rod or perch of 16^ feet, by a thickness of \\ brick, or what is 
called in England 14 inch work, so that if a wall is thicker or 
thinner than this standard, it has to be reduced to that thickness, 
and hence the term so frequently used of so many rods of reduced 
hrick-work. 

The square of 16 J lineal feet is 272.25 square ieei, but by cus- 
tom the fraction is cancelled, and 272 square feet are considered 
as one rod of work, consequently 136 square feet will be half a 
rod, and 68 square feet a quarter rod. 

936. Brick-work is measured by a pair of five feet wooden rods, 
divided on both sides into feet, and half and quarter feet, any di- 
mension less than three inches being taken by the estimation of 
the eye, while the rod is applied. The operation is usually con- 
ducted by three persons, viz: the Engineer or Measurer, who 
writes in the measuring book, directs what measures are to be 
taken, and inspects their correctness before he enters them, and 
two assistants or rodmen, each of whom carries one rod. The 
rods, when used, are made to coincide with, or be parallel to, either 
horizontal or vertical joints, and the first rod having been applied 
to the work in its proper position, is held there by the first man, 
while the second causes the end of his rod to abutt against its end: 
the second rod is then in turn held firmly against the work, while 
the first man moves onwards and places his rod in the same position, 
and so on, until the whole horizontal range of work is measured, 
when the entire length is put down as one dimension. 

Vertical heights are obtained by the same process, the mea- 
surers using ladders, or scafiblding, or climbing up to the openings 
of windows, should no more convenient mode present itself. The 
rods ought to be so flexible as to bend readily round arches or cir- 
cular openings, for getting their dimensions. 

937. Who ever has charge of the superintendence of brick- 



504 OP BRICK-WORK. 

work ought to measure, and keep a record of all foundations, foot- 
ings to walls, and other underground work, as soon as it is done; 
or at any rate before the soil is returned into the trenches of the 
foundation, because such brick- work then becomes invisible, and 
if its measurement has not been previously recorded, it will be 
necessary to dig holes for examining and measuring it afterwards, 
and this occasions much additional trouble and delay. 

938. Whenever the thickness of brick-work changes, a new 
dimension must be taken, and a new entry made in the book; but 
any work that is of the same thickness and at the same level, 
mav be included in the same dimension. 

939. The dimension book is ruled with three narrow columns 
on the left side of each page, the remainder being left for writing 
descriptions and remarks; being the same as the stone measuring 
book referred to (897), but there is no moneying column on the 
right hand side. 

940. Brick-work is sometimes cubed, (particularly when walls 
are very thick,) but the usual mode of measurement is to merely 
measure the square superficies on the face of each wall, and 
write against it the thickness of the wall in bricks and half bricks. 
The dimensions, as taken, are written down one under the other, 
with a line under each when complete, in the second column of 
the book, and the third or next column is left blank for the inser- 
tion of the products or multiplication, or squaring of those dimen- 
sions, which is never done at the time of measuring, but is left to 
be performed in the office at home, and is usually the lot of the 
junior clerk, or clerks, in that office. The working of the opera- 
tions is performed on a slate or waste paper, and the result above 
carried to the third column of the book, while the fourth or wide 
column, contains the thickness of the wall in bricks (when cubing 
is not used), an account of the place where the dimensions occur- 
red, and any other necessary observations. 

941. When brick-work is cubed, take the long, or horizontal 
dimension first, and set it down in feet and inches in the second 
column; next, take the perpendicular height, and set that down 
in a second hne immediately under the first dimension; lastly, take 
the thickness of the wall in feet and inches, and write it as a third 
line, directly under the two others, and draw a line across the 
column, because that dimension is complete. In like manner pro- 
ceed to take other dimensions, and set them down in the same 
order and manner, until the top of the building is reached, or the 
work otherwise finished. Each complete dimension will now con- 
sist of three members, a length, a height, and a thickness, and 
these have now to be worked out. The length multiplied by the 



OP BRICK-WORK. 505 

height will give the superficies, and this multiplied by the thick- 
ness will give the solid or cubic contents of that portion of the 
wall, which must now be entered in the third column. When all 
the quantities have thus been separately cubed and carried to the 
third column, that column may be cast up, and its sum will be 
the total number of cubic feet and inches contained in the work. 
If the work has been agreed to be paid for by the cubic foot, as 
is often the case, this is all that will be wanted: but if the cubic 
measure has to be reduced to rod measure, multiply it by 8 and 
divide the product by 9, when the quotient will be the rods of re- 
duced brick-work, because the standard thickness of 1^ bricks 
should be |ths of a foot. 

942. When brick-work is measured by the more usual process 
of taking the thickness of the walls in bricks and half bricks, only 
two dimensions will appear in the second column of the measuring 
book, viz: length and height; the third column is left blank as be- 
fore, and the thickness of the wall is placed before the description 
of the work, as will appear in the following short example of keep- 
ing a bricklayer's measuring book. 

A M, in the following heading, means all materials, i. e. the 
workman finds bricks, mortar, labour, scaffolding, and all tools and 
materials for executing the work. L and M is, in like manner, used 
to signify labour and mortar only, and L only, when the bricklayer 
is provided with all materials, and has to furnish labour alone. 
Brick-work is contracted for under one or other of these conditions. 
The headings of all measuring books should be full and explicit, 
because they are often produced in courts, or at arbitrations, as 
evidence; consequently they should contain no erasures, except 
such as are made by striking the pen through articles and writing 
them again; neither should any leaves be torn out. The time 
when the work was done should be particularly specified on ac- 
count of the price, for as both materials and labour fluctuate in 
value with times and seasons, so by specifying the date of the 
work, prices accordant with that date, can always be obtained. 

Measurement of Bricklayer's Work 

A M, executed by A B for C D, between January and June, 1832, 
in building additions to Jefferson Medical College, in Philadelphia, 
as measured this 27th day of July, 1832, by J. M. 



64 



506 



OF BRICK- WORK. 





58 
1 


6 
6 


87 

43 

43 

632 

125 

36 

22 

88 
44 
44 
649 
80 

14 

3 

9 

906 


9 
6 

1 
7 

8 

8 
6 

6 
3 
3 

9 

8 

9 


8 


4 brick footing to west wall. 




58 



9 


3 J brick footing to do. 




57 


6 
9 


3 brick footing to do. 




56 
11 


8 
2 


2 J brick wall of basement story. 


4) 


6 
4 


6 
10 


J brick DD in recess pannels. 


4) 
. 4) 


4 

7 


10 
6 


2^ bricks DD 4 semicircular arches. 

run of 9 inch gauged arches over same, 4 
inches thick. 

4 brick footing to north and south walls. 


2) 


29 

1 


6 
6 


2) 


29 


6 
9 


3J brick do. to do. 


2) 


29 


6 
9 


3 bricks do. to do. 


2) 


29 
11 


6 
2 


2-^ bricks north and south walls. 




9 

8 


6 
6 


2J bricks DD gateway in south wall. 




4 
3 


6 
3 


2^ bricks DD window in do. 




5 





run of 9 inch gauged arch over same, 4 

inrlips! fliiplr 




12 





run of do. over gateway. 




56 
16 


8 



2 bricks — west wall above first set-off. 








1 



OP BRICK-WORK. 



507 



2) 

6) 
6) 



2) 



6) 



6) 



6) 



2) 



No. 14. 



29 6 
16 



10 6 
5 



5 



6 6 



56 8 
11 3 



29 6 
11 3 



4 

2 3 



5 3 
3 6 



3 9 



56 8 



32 



13 



21 



944 

315 

56 10 

29 3 

637 6 

663 9 

54 



2 bricks north and south walls above 1st 
set-off. 

2 bricks DD windows. 

2 bricks DD semicircular arches over same. 

run of 9 inch gauged arches, 4 inches thick, 
over same. 

1 J bricks, west wall in third story. 



1 J bricks north and south walls in 3d story. 



1 J bricks DD openings for ventilators. 



113 3 1^ bricks DD windows. 



18 

396 4 

64 

63 

24 6 



run of 9 inch camber gauged arches 4 inches 

thick to windows. 
1 brick in pediment finishing west wall and 

rising 14 feet in centre, 
run cutting to ramps of do. 

1 brick DD semi window in pediment. 

run of 14 inch gauged arch over same. 



wrought stone sills bedded and fixed to win- 
dows, &c. &c. 

The above work abstracted in Abstract Book, No. 5, page 60. 

943. The building referred to in the above entries, was an ad- 
dition, consisting of three walls, to a former building, which con- 
stituted the fourth side to the new work; consequently, there were 
two new walls on the north and south sides, and only one on the 
west. The net external length of the new building, as it ap- 
peared above ground, was 56 feet 8 inches, and its breadth 31 feet 
9 inches. As the measurement always commences at the bottom 
of a building, the first dimension to be taken is the lowest footing 
or foundation of the largest or principal wall, which is 58 feet 6 



508 OP BRICK-WORK. 

inches long by 1 foot 6, or six courses high, and four bricks thick, 
as entered at the commencement of the measuring book. Then 
the footing diminishes to 3^ bricks, which makes a separate dimen- 
sion necessary; and this is 58 feet long by 9 inches high. The 
footing still diminishes to 3 bricks, and is accordingly set down as 
57 feet 6 inches, by 9 inches high in 3 bricks. All this work is 
imderground, and unseen, and consequently should be measured 
before the earth is refilled into the foundation trench. The wall 
of the basement story next appears above ground, and this is 56 
feet 8 inches long, by 11 feet 2, in 2^ bricks up to the first offset 
or line, where the wall diminishes in thickness. This wall is, 
therefore, all taken at one dimension, as if it was of even thick- 
ness throughout; but it is not so, for it is worked in pannels, 
(918,) each of 6 feet 6 inches high, and 4 feet 10 inches wide, 
showing a break of half a brick, and as these pannels are four in 

A fi 

number, the dimension is set down as 4) . ^ ,. in J a brick DD, 

which shows that the product of this dimension is to be taken 4 
times over, and the DD indicates that the sum so obtained, and ^ 
a brick thick is to be deducted from the amount of the 2^ brick- 
work last measured: DD being the common mark to denote de- 
duction or subtraction. Each of these pannels is surmounted by 
a semicircular arched opening quite through the 2-J brick wall for 
lighting the lower story. Hence the dimension 4) 4 feet 10 inches, 
in 2j bricks DD for 4 semicircles, which shows that the area of a 
semicircle of 4 feet 10 inches in diameter is to be found in square 
superficial feet (176), and is to be deducted at 2j bricks thick from 
the 2J brick wall. Each of these semicircular openings is finished 
or ornamented by a gauged arch, (see gauged and camber arches 
in the chapter on arches,) which is charged by superficial mea- 
sure, obtained by bending the measuring rods over the central 
part of such arches, which gives a length of 7 feet 6 inches as set 
down in the second column, to be multiplied by 9 inches, the width 
of such arch, which is 4 inches or ^ a brick thick. No deduction 
is however made from the quantity of ordinary brick-work on 
account of this 4 inch work, which may thus appear to be taken 
twice into the computation, but this is not the case. The 4 inch 
gauged arch is measured in with the general mass of brick-work, 
and this accounts for the surface of the arch being taken in super- 
ficial measure only, without any regard to its thickness; an allow- 
ance being made upon the superficial measure, and not the solid 
work of such arches, for the extra trouble in constructing them; 
and as these arches occur 4 times, all of the same size, the dimen- 
sion 7 feet 6, is preceded by 4) in the first or left hand column, 
which shows that the dimension is to be taken or multiplied 4 times. 



OF BRICK-WORK. 509 

The three next dimensions are all alike in length, and apply- 
to the underground footings of the north and south walls, which 
are measured separately by the rods, and being found alike, there 
is no occasion to repeat the writing of the dimensions in the book, 
but they are preceded by 2) in the first column, to indicate that 
they are to be reckoned twice in the casting up as before explain- 
ed (898). And the same observation applies to the next dimen- 
sion 29 feet 6 inches by 11 feet 2, being the length and height of 
the two end walls up to the first floor or set-ofF; but two deductions 
in 2^ bricks it will be seen occur in the south wall, for a gateway 
and a window made through it, as expressed by the two dimen- 
sions 9 feet 6 by 8 feet 6, and 4 feet 6 by 3 feet 3 inches; and 
these are followed by the two single dimensions 5 feet and 12 feet, 
being the lengths of the two gauged arches over these openings, 
to be treated as before. 

The two succeeding dimensions give the lengths and heights of 
the three exterior walls, (one of them being taken twice,) and 
which are taken separately, because these walls are thinner than 
those that preceded, being only 1^ bricks thick. In the walls six 
windows occur having arched or semicircular tops, consequently 
each window requires two dimensions, viz: 10 feet G inches high 
by 5 feet wide for the lower or rectangular part, and a single di- 
mension of 5 feet being the diameter of the semicircular head. 
These dimensions have 6) prefixed to them, because the same 
sized windows occur six times over, and that is likewise the case 
with the semicircular gauged arches that surround them. The 
two next dimensions (the latter having 2) prefixed) give the dimen- 
sions of the three walls of the upper story, which might have been 
taken at once with those of the lower story, because no set-off 
occurs, and they are still Ij bricks thick; but on account of the 
convenience of taking the height of this part from one of the win- 
dows, it was made a separate dimension. This upper range of 
waUing, like the last, contains six air holes or ventilators, but as 
they have straight, instead of arched tops, and are all alike, they 

can be expressed by the simple entry of 6)^ q> and the like of 

the six windows, 6)5 feet 3 by 3 feet 6. The six gauged arches 
over these windows, each 3 feet 9 inches long, need no explana- 
tion after what has been stated concerning the others. 

The last wall to be measured is the triangular gable end which 
finishes the west wall of the building, and which is only 1 brick 
thick. This has but one dimension 56 feet 8 inches set against it, 
which is the entire length of the building, but in the right hand 
column of remarks, it is stated to be a pediment of 1 brick thick, 
rising to the height of 14 feet in the centre. A pediment is 



510 OF BRICK-WORK. 

always a triangular form, consequently this portion of wall is a 
triangle having a base of 56 het 8 inches long, and a height of 14 
feetf and its superficial area must be found by Problem XXX (173). 
Each raking or sloping side of this triangular wall measures 32 
feet, therefore 2)32 or 32x2, will give the quantity or length of 
cutting to the ramps of this wall (920), to make it agree with the 
slope of the roof. Lastly, a semicircular arched window of 13 feet 
diameter occurs in this pediment, which has to be deducted from 
the 1 brick wall, and then the superficies of a 14 inch gauged 
arch over the same must be added, which completes the measured 
work. Fourteen stone window sills it appears were fixed in the 
different windows, and these have to be charged at a certain price 
for each according to their size and length. 

944. The foregoing is but a short example of the method of 
making entries in a measuring book, and these entries will, of 
course, become extensive in large buildings. It will be observed 
that while these measurements are taking and entering in the 
book, the third column is constantly neglected, or left blank or 
open. But when the measurement is finished, all the dimensions 
have to be worked out or squared on waste paper or a slate, and 
the results so obtained are the quantities to be set down in the 
third column. Thus on multiplying the first dimension 58 feet 6 
by 1 foot 6, the product is 87 feet 9 inches, which is entered in 
the third column, and the same applies to the three dimensions 
that follow. The fifth dimension is 6 feet 6 inches by 4 feet 10 
inches, the product of which would be 31 feet 5 inches. But this 
dimension is preceded by 4) in the first column, showing that it 
must be multiplied or taken 4 times over, thus prod'ucing 125 feet 
8 inches, which is accordingly entered in the third column, and 
the sixth and seventh dimensions are treated in the same manner. 
The 8th, 9th, 10th, and 11th dimensions being preceded by 2) are, 
for like reasons, doubled before thev are set down. The dimen- 
sions from the 12th to the 16th having no coefficient or multiplier 
prefixed to them, are treated as simple quantities, and of course 
are entered as their actual results; but the 18th, 19th, and 20th 
are multiplied by 6, and so on of the others that follow. 

945. In this way the whole third column of the book is filled up, 
and that accomplished, the contents of this column has to be parted 
or separated into distinct parcels or columns, each containing the 
same kind of work, which operation is called abstracting dimen- 
sions, and this is done in a separate book prepared for the purpose 
called the abstract book, which is ruled in a number of vertical 
columns, one of which is appropriated to each variety of work, 
and the next adjoining column to the deductions from that same 



OF BRICK-WORK. 



511 



kind of work, and the columns are headed accordingly, as in the 
following example. 

946. Abstract of brick-work done at Jefferson Medical College, 
Philadelphia, as measured 27th July, 1832, as per dimensions 
entered in Measuring Book, No. 40, beginning at page 1. 



CO 


00 

1q 


o 


v< 
o 

--H 


•s 




ricks 
D. 




93 

O 

•^ 


CQ 


pqQ 


pq 


M 


pa 




WQ 


MQ 


Sh 

pa 


Tt< 


■^ 


Ho? 


cc 






CM 


-*< 


(M 


87 9 




43 6 


43 1 


632 


7 


36 8 


125 8 


906 8 


88 6 




44 3 


44 3 


649 





80 9 
14 8 




944 


176 3 




87 9 


87 4 


1281 
132 


7 
1 


132 1 




1850 8 
371 10 


1149 


6 


1478 10 



paQ 


a 

Sh 

pa 

Ha 

1— t 


IJ Bricks 
DD. 


o 

• 1— ( 
S-l 

pa 


1 Brick 
DD. 


Super, of 
gauged arch. 


Feet run of cut- 
ting to ramps. 




315 
56 10 


637 6 
663 9 


54 
113 3 


396 4 


63 


22 6 
3 9 
9 

29 3 
18 
24 6 


64 


No. 14. 


371 10 


1301 3 
167 3 


167 3 


396 4 
63 




1134 


333 4 


107 



947. The order of succession of the columns in the abstract 
book, need not be attended to; the usual method of making the 
entries, being to take the dimensions as they occur in the mea- 
suring book, and write them off into the abstract book, heading 
the column in which they are entered, whenever a particular kind 
or thickness of work occurs for the first time; and then entering 
all repetitions of the same work as they occur in the same 
column. Thus the measuring book begins with 87 i^^i 9 inches 



512 OF BRICK-WORK. 

of work 4 bricks thick; and accordingly the first column of the 
abstract book is headed with "4 bricks," and the dimension 87 9 
is written in the column under it. The next column to the right 
is headed "4 bricks DD," and is for deductions in four brick- 
work, of which there are none in the example, consequently the 
column remains blank throughout; and it is only introduced here, 
to show where the deduction column should be placed. 

The next dimension is 43 feet 6 in 3j brick-work. The third 
column is therefore so headed, and the amount set down in it; and 
so of the fourth column, which contains the third dimension, 43 
feet 1 inch in 3 bricks; and as no deduction occurs in the exam- 
ples, either in the S^ or 3 brick-work, so the deduction columns 
have purposely been left out. The fourth dimension is in 2J brick- 
work, and the fifth column of the abstract book is allotted to it; 
but the example ofifers two distinct kinds of deduction from this 
variety of work, viz: one of only half a brick thick and the other 
of the whole thickness, therefore two distinct deduction columns 
here become necessary, one of which is headed **2|^ bricks DD," 
and the other "-| brick DD." In this manner every distinct kind 
of work, and every deduction from such work has a separate 
column appropriated to it, so that all the dimensions of the mea- 
suring book become classified and arranged; which being done, 
each column is to be separately cast up at its bottom, and the sum 
will show the total quantity of work of each particular kind. 
Thus we find that we have a total of 176 feet 3 inches superficial 
of work 4 bricks thick, and 107 feet super, of gauged arches, &c. 
in the whole building. When deductions occur, the sum of the 
deductions must be subtracted from the sum of similar work. 
Thus by the fifth column it will appear that we have 1281 feet 7 
inches super, of work 2 J bricks thick: but the sum of the 2^ bricks 
DD column, is 132 feet 1 inch, which sum must be subtracted 
from 1281 feet 7 inches, and will leave 1149 feet 6 inches of ac- 
tual work to be paid for. The same thing occurs in the seventh, 
ninth, and twelfth columns containing respectively 2 bricks, 1^ 
bricks, and 1 brick-work. 

948. Having thus abstracted, or sorted, the several varieties of 
work, the next operation is to reduce them all to the standard 
thickness of one and a half bricks, in order to get the work into 
rod measure, and 

The Rule for Reduction 

is to multiply the superficial measures obtained by the number of half 
bricks in the thickness of the work, and divide the product by 3, which 
will give the superficial standard, or rod measure. 



OF BRICK-WORK. 513 

The first quantity, 176 3, in the abstract book must, therefore, 
be nnultiplied by S, because the work is 4 bricks, or 8 half bricks 
thick, and the product must be divided by 3, viz: 

176 ft. 3 in.x8=1410ft.-^3=47d feet superficial. 

The second quantity, 87 feet 9 inches, being in 3^ bricks, must 
be multipled by 7 (half bricks), and be divided by 3. 

S7ft. 9x7=614ft. 3in.-T-3=204feet 9 inches. 

The third quantity, 87 feet 4 inches, being in 3 bricks, has to 
be multiphed by 6 for division; but it may be here remarked that 
whenever the thickness of a wall amounts to an even multiple of 
the standard thickness, a shorter operation may be adopted; be- 
cause it is only necessary to multiply the superficies given in the 
abstract book by the number of times the standard thickness is 
contained in the work, and this of course will give its reduction. 
Thus 87 feet 4 inches of work 3 bricks thick, is evidently the 
same as twice that quantity at 1| bricks thick, or the standard 
thickness is contained twice in the thickness of the wall, conse- 
quently this dimension has only to be doubled or multiplied by 2, 
making 174 feet S inches of reduced work. 

The fifth column contains work 2j bricks thick, which, of 
course, has to be multiplied by 5 (half bricks). 

The seventh column is work |^ brick thick, consequently no 
multiplication is necessary, but the gross quantity is at once divided 
by 3, because work in |^ a brick thick, is only equal to one-third 
of the standard thickness. 

The eighth and ninth columns contain work in 2 bricks, and this 
is multiplied by 4 and divided by 3. 

The tenth and eleventh columns contain brick and a half work, 
and this requires no operation upon it, since the superficial mea- 
sure is of the proper standard thickness in the first instance. 

The twelfth and thirteenth columns are work in one brick, con- 
sequently equal to only two-thirds of the standard thickness. We 
may, therefore, take two-thirds of the measured quantity; or may 
obtain that same result by multiplying the measured quantity by 
2 and dividing by 3. 

The fourteenth, fifteenth, and sixteenth columns require no ex- 
planation. The fourteenth gives the sum of the superficial mea- 
sure of all the gauged arches about the same building; the 
fifteenth the lineal measure of all the cutting to ramps; and the 
sixteenth the number of stone window sills set. The first of which 
is to be priced at per foot super.; the second at per foot running 
measure, and the last at per piece. 

949. All the dimensions being thus consolidated and reduced to 
a brick and a half thick, the several reduced quantities have now 
to be added together, and their sum will be the number of super- 
65 



514 OF BRICK-WORK. 

ficial feet at reduced thickness, and this being divided by 272 will 
give the number of rods of work. The remainder (if any) must 
be again divided by 136 or 68, to obtain half and quarter rods, 
and the final remainder will be superficial feet, each to be charged 
at the 272nd part of the value of a whole rod of work. 

950. From the above observations, it will appear, that all doors, 
windows, and other openings made in walls, are subject to deduc- 
tion from the quantity of work; but no deduction is made for bond 
timber, or small holes left for receiving the ends of girders or 
other timber. No deduction is made for fire-places and their flues 
or chimneys, in valuing work for labour and mortar, or labour only, 
because it is considered that the extra labour and trouble in their 
formation, is equivalent to such deduction. But when work is 
done finding all materials, the quantity of material that would be 
necessary to fill up such openings, should be deducted. 

951. The value of brick-work is determined in the following 
manner. 

In London 4,500 bricks are allowed to each rod of reduced 
brick-work, being an ample quantity to cover waste. 

37|^ struck bushels of quick lime, and 

54 heaped bushels, or 66 struck bushels of sand. 

The hire of one bricklayer, and one labourer to mix up mortar 
and carry the materials, including the use of scaffolding, ladders, 
tools, &c. is considered equivalent to ten dollars for each rod of 
work of the best kind; therefore, knowing the price of labour and 
materials, the net cost can be obtained, and upon this, 15 per cent, 
is added for profit to the master. 

The bricks of the United States being smaller than those of 
London, more mortar joints as well as more bricks will be neces- 
sary for the same bulk of work. This addition amounts to from 
^th to ^th upon such work as the writer has examined. 

952. The most usual manner of contracting, and paying for 
brick-work in the United States, is by the 1000 bricks laid, or if 
measured, the measurement is taken in cubic feet, and charged 
according to the nature and neatness of the work. The following 
particulars may assist in ascertaining the value of work. 

Bricks. 
A bricklayer and labourer can, in a day, lay in inside 

walls with rough joints, 1,200 

In external walls with joints struck smooth, ' - - 1,000 
In front walls with facings, taking facing and backing 

together, --.-_-.- 500 

In arches to vaults, cellars, &c. _ - - - 750 

In paving flatwise, including levelling the ground, - 2,000 



1 


121 




50 


1 


121 




75 




121 


9 


37J 


1 


62i 



OP BRICK-WORK. 515 

One cask of lime (3^ bushels), and two cart loads of sand (27 
bushels), will lay 1,000 bricks in mortar. 

17 London, or 22 Philadelphia bricks, make a cube foot of 
brick-work laid in mortar. 

The value of brick-work laid by the thousand, in party or 
internal walls, with rough joints, is nearly as follows, in New York 
and Philadelphia. 

1,000 common hard bricks delivered at the work, $5 75 

1 cask of good lime, do. 

2 loads of sand, do. 
Bricklayer | of a day, 

Labourer f of a day, - - - - 

Use of scafifolding and tools, - - - 



Profit, - - 

^11 00 

or 1 1 dollars per thousand, producing 46 cubic feet at 24 cents 
per foot. 

For brick-work in neat external walls with struck joints. 

1,000 common hard bricks delivered, - ^5 75 

1 cask of best stone-lime, - - - 

2 loads of sand, - - - _ - 
Bricklayer one day, _ _ - _ 
Labourer one day, _ , *- _ 
Use of scaffolding and tools, - - _ 



Profit, 

^12 00 

or 12 dollars per thousand, producing 46 cubic feet at 26 cents 
per foot. 

In vaults and arches all will remain the same except the brick- 
layer, who will be allowed H day. And in the very best facing 
work, laid with fine mortar joints in the best manner, the brick- 
layer and labourer will require 3 days each to the 1,000 bricks. 

A superficial foot of facing to fronts will take 8 bricks. 

A superficial yard, or 9 square feet of paving will take 42 bricks. 

One bushel of Roman or LLydraulic cement, mixed with two 
bushels of clean sharp sand, will lay 150 bricks; or will cover 4 
square yards of plastering on brick-work. 



1 


50 




50 


1 


50 




87J 




12^ 


10 


25 


1 


75 



516 OF CARPENTRY. 

As before stated, 306 cube feet of brick-work make a rod of 
work reduced to the standard thickness. 

Fire-work, from the extreme care and nicety requisite in its 
execution, is seldom measured, but is done as day work. This is 
also the case with all small jobs which cannot be worked in a 
speedy and straight forward manner, or which require more time 
and attention than is necessary in building regular walls. Under 
pinning to walls is of this description, being the building of small 
portions of wall at a time, from the foundation up to a wall, or 
frame building previously erected, for the purpose of supporting 
and sustaining it. The whole foundation of a building, when 
defective, is sometimes renewed in this way by taking down a 
small portion of the old wall at a time, and replacing it with new 
work well wedged up, before another portion of the old wall is 
taken away. 

With the above data and particulars, it is presumed no diffi- 
culty can arise, either in the measuring or setting a value upon 
any kind or quantity of brick- work. 

Section 3. — Of Carpentry, 

953. Carpentry is the art of cutting out and fixing together 
pieces of timber for the purposes of architecture, constructing 
machinery, and in general for all considerable structures, which 
operation goes under the general name o^ framing timber. 

Although carpentry is confined to wood-work exclusively, it 
requires frequent assistance from the metals, particularly iron, as 
in straps, ties, screw-bolts, wedges, &c., in order to give greater 
strength to the work. With the making of these articles, of 
course the carpenter has nothing to do, but it is a part of his busi- 
ness to fix and apply them judiciously in their proper places. 

954. Carpentry is divided into two distinct branches, called 
Carpentry and Joinery, and the workmen who pursue them are 
called Carpenters and Joiners, but the two branches are almost 
constantly conjoined and followed by the same workmen. Car- 
pentry is the art of framing or putting timbers together so as to 
produce strength, stability and duration, without regard to neat 
finishing, except only in the joints or parts of union, the remain- 
ing part of the timber being left rough as it comes from the saw. 
Joinery, on the contrary, is the work of putting small pieces to- 
gether in a smooth and finished manner, planing the surfaces, 
forming mouldings, and other ornamental work in which beauty 
is more important than strength. The work of the joiner, there- 
fore, generally follows that of the carpenter, and is frequently 
used to hide the unsightly appearance of his work. 



OP CARPENTRY. 517 

Thus in building a frame house, the putting up of the studs or 
quarterings that are to form the external parts and internal par- 
titions, the joists for receiving the boards of the floors, and the 
preparation and fixing of the roof to receive shingles, tiles, or other 
covering, would all be styled carpenter's work: But the making 
and fixing (called hanging) of all doors, window sashes, shutters, 
shelves, and even the planing and laying of the floor boards are 
the province of the joiner. It will thus appear that while taste, 
combined with neatness of execution, constitute the chief perfec- 
tions of a joiner, that the carpenter must, in addition to these 
qualifications, possess science and skill to judge of the strength of 
the materials he has to use; and should also understand the effects 
that will be induced by the weight and pressure of separate 
pieces acting against each other when conjoined; he must know 
how to distribute these forces to the greatest advantage, and also 
how to unite the pieces together so as to produce the greatest 
strength out of a given quantity of material. On this account 
the carpenter ranks as the highest grade in the two branches, for 
scientific carpentry is among the most beautiful of the applica- 
tions of the principles of mechanical philosophy to the useful pur- 
poses of life. 

955. In England a third kind of workman has been introduced 
by the Engineer, v/ho, in addition to the usual qualifications of 
the carpenter and joiner, has higher attainments, and is more 
versatile in his operations. That is the Millwright. Carpenters 
who are in the habit of building houses and ordinary buildings, 
generally work in straight lines, and construct that which has 
to remain stationary. They cannot therefore be expected to be 
so expert in constructing circular work, or be so well acquainted 
with the strength and other qualities of that which is to move, as 
one who devotes his whole time to such business. A carpenter 
who might build an excellent and durable house, would probably 
fail in his first attempt to make a good coach-wheel, much more to 
construct a perfect water-wheel for a mill, to hang it on its shaft, 
and construct the cog or toothed wheels it has to drive. Such busi- 
ness belongs particularly to the millwright, who is brought up 
and educated for this sort of business. He is generally a good and 
perfect workman in wood; but a good millwright is also able to 
work at the forge, to turn, to set out work with accuracy, such 
as the forms for the teeth of wheels to move into each other with 
the least friction, and he should understand pump-work and hy- 
draulic machinery. In constructing a mill or manufactory in 
England, the external building is alone entrusted to the ordinary 
class of masons, bricklayers, carpenters, and other workmen, and 
the millwright is called in to put up and fix the steam engine, 



518 OF CARPENTRY. 

water-wheels, or other machinery that has to perform the me- 
chanical operations. This class of workmen, from their scarcity 
and skill when good, are paid at a higher rate of wages than any 
other artificers in the building line. 

956. As a knowledge of carpentry is more useful, and indeed 
necessary to the Engineer than joinery, so the observations about 
to be made will be confined almost exclusively to that branch of 
the business. 

The theory of carpentry is founded on two distinct portions of 
mechanical science, namely, a knowledge of the strains to which 
framings of timber are exposed, and a knowledge of their relative 
strength. The first of these may be investigated by the mecha- 
nical laws which regulate the composition and resolution offerees, 
and the last must be derived from principles such as have been 
laid down in the third section of our ninth chapter. 

957. To take the simplest example, suppose a body or any part 
of a body to be at once pressed in the two directions a b, a c, PL 
VI., Fig. 185, and if the intensity or force of those pressures be 
in the proportion of these two lines, the body is affected in the 
same manner as if it were pressed by a single force acting in the 
direction a d, which is the diagonal of the parallelogram ah d c 
formed by the two lines, and two others drawn parallel to them; 
and the intensity of the force represented by a d, will have the 
same proportion to the intensity of each of the other two that a d 
has io ah or a c. To make this still plainer, let us suppose a b 
and a c to be two sticks or pieces of wood, supported at the points 
h and c while they touch each other at a, and suppose a weight to 
be applied upon them at a; then their joint power to resist that 
weight will be as a d, consequently the longer a d can be made, 
and the greater resistive power they will possess. But a d can 
only be lengthened by diminishing the angle 6 a c, or making it 
more acute, and the maximum of elongation will be when a h and 
a c come into contact with each other or form no angle at all, or 
an infinitely small one, for then a d will be equal to their con- 
joined length, and the pressure will be exerted in the direction of 
their length or in the most favourable position for strength. If, 
on the contrary, the angle h a c was rendered very obtuse, as in 
Fig. 186, then the diagonal a c? becomes much shortened and their 
power of resistance proportionably decreased until the angle is so 
opened as to become a right line, when all power of resistance 
vanishes, and they will be incapable of sustaining their own 
weight, since they are supposed to be iree, or not attached to- 
gether, or to. the points that support their ends. This general 
principle may therefore be considered as established, that the 
more open or obtuse we make the angle against which any thrust 



OF CARPENTRY. 519 

or force is exerted, and the greater are the strains which are 
brought on the struts or ties which form the sides of that angle. 

958. A strut in carpentry is any piece of tinnber that is subject- 
ed to a compressing force in the direction of its length, and which 
consequently acts and becomes effective by its stiffness. A tye, on 
the contrary, is any piece that is subjected to an extending force, 
or the place of which might be equally well supplied by a rope. 
In framing it is sometimes difficult at first sight to determine 
whether a piece of timber is a strut or a tye, but the question 
will generally be answered by considering whether a rope or 
flexible chain could supply the place of the piece, and if not, it 
must be a strut. 

959. The combinations of pressure are of so much importance 
that they must be farther examined by some practical examples. 
Thus suppose an upright beam b a, Fig. 187, pushed in the direc- 
tion of its length by a load b, and abutting on the ends of two 
beams a c, a d, which are firmly resisted at their extreme 
points c and d which rest on two blocks, but are not fastened to 
them: These two beams can resist no way but in the directions 
c df d a, and therefore the pressures which they sustain from the 
beam and load b a are in the directions a c, a d. We wish to 
know how much each sustains? Produce b a to e, taking a e from 
a scale of equal parts to represent the number of tons or pounds 
by which 6 a is pressed. Draw e jT and e g parallel to a d and a 
c; then admeasured on the same scale will give the number of 
pounds by which a c is strained or compressed, and a g will give 
the strain on a d. 

960. It must be remarked that the length of a c or a d has no 
influence on the strain arising from the thrust of b a, while all the 
directions remain the same. The effects, however, of this strain, 
are modified by the length of the piece on which it is exerted. 
This strain compresses the beams, and will therefore compress a 
beam of double length twice as much, and this may change the 
form of the assemblage. If a c, for example, be much shorter 
than a d, it will be proportionably less compressed. The line c a 
will turn about the centre c, while d a will hardly change its po- 
sition, and the angle cad will grow more obtuse by the point a 
sinking down. The artist will find it of great importance to pay 
minute attention to such circumstances as these, that he may 
learn to know the change of shape necessarily resulting from mu- 
tual strains. By such changes, strains are often produced in 
places where there were none before, and frequently of the very 
worst kind, tending to break the beam across. To show what a 
prodigious change in strength may be produced even while the 
timbers remain the same, let us suppose one of the pieces of tim- 



520 OP CARPENTRY. 

ber referred to in the last figure, to be altered in its relative posi- 
tion as shown by the dotted lines at oD in the same figure. This 
change will increase the strain on both the pieces, for a g will be 
nearly doubled, and a f will be four times greater than before, 
because now e/must be drawn as eF to be parallel to aD. The 
diagonal line a e, it is true, will not be varied in length, but the 
line e/will be greatly elongated, and thus change the proportion 
that before existed. 

961. So far we have supposed the beam and weight a 6 to be 
placed above the two inclining pieces of timber, and pressing ver- 
tically upon the point of their contact; but it will be evident that 
the effect of pressure will not be altered if we take away this 
beam and weight, and in lieu of it attach a rope at a, which rope 
may be represented by the line a e, while to the lower end of 
this rope we fix a weight w that shall be exactly equal to the 
weight of the beam and weight a b. Nothing, as regards pres- 
sure, will be altered by this change, and the parallelogram f a e 
g, with its diagonal a e, will still remain the proportional repre- 
sentative of the forces. Or we may take the half of the parallelo- 
gram or triangley* a e for their representative, since the side a e 
is to the side a f as the weight 6 or W is to the pressure in the 
direction of a f: also -as a e :f e '. : the weight to the pressure in 
the direction of the beam a g. There is, however, no necessity 
for supposing any extraneous weight 6 or W to be applied to 
these beams, since their own weight will keep them in their posi- 
tions, and is frequently the only load to be guarded against. 

962. These simple principles lead at once to a consideration of 
the construction of the roofs with which buildings are covered, for 
roofs are generally formed of sloping timbers disposed nearly as 
above described, and so placed for a two-fold object, viz: obtain- 
ing strength and throwing off rain and snow, which is well accom- 
plished by the inclined position. 

963. The sloping timbers of a roof are called rafters and oppo- 
site rafters, or a pair of rafters are usually of the same length, 
and made to slope in the same angle, so as to throw their meeting 
or angular juncture (which is called the ridge of the roof) into 
the central line, or midway between the two walls on which the 
roof is supported. In this manner the weight of the roof, which 
is all it has to bear or sustain, is equalized or thrown equally on 
the two opposed rafters, and the two walls that support them, as 
in Fig. 188, where k and / represent the two rafters meeting in a 
point or ridge at m, and resting on the side walls n n. The 
effects of gravitation upon such a construction will be equal on 
each part of each beam, but its general effect may be represented 
by a plummet or other line m o let fall from the ridge at right 



OP CARPENTRY. 521 

angles to the horizon, and by drawing lines parallel to each rafter 
from any one point jt? in this perpendicular, those lines, as^ k and 
p /, will be equal to each other, thus showing that the strain on 
the two rafters is equal. Still as gravity will be constantly acting 
on such a roof, tending to depress it in the direction m o, it cannot 
be a strong or stable structure, and will even endanger the build- 
ing on which it is placed: For, admitting the rafters to be stiff 
and inflexible, they can give way in no manner but by spreading 
or extending at their feet, or lower points n n, and if the weight 
of the roof is greater than the strength of the walls can withstand, 
there is no doubt but that this effect will take place, and that 
roof and walls will both come to the ground. There are, how- 
ever, several methods of giving strength to such a structure, and 
two of these were constantly resorted to in the reign of pointed, 
or as it is generally called, Gothic architecture. The first of 
these was the application of a buttress or counter-fort to the out- 
sides of each wall at all those places where such a framing of tim- 
ber was used, thus giving strength to the walls at the places where 
it was required, as in Fig. 179, where it will be perceived there is 
nothing to withstand the lateral spreading of the rafters s t but 
the strength of the walls, assisted by their buttresses, and on this 
account the ridge angle of such roofs was always made acute. 

964. Secondly, a cross beam called a collar beam, was intro- 
duced to tie the two rafters together near their central parts, as 
at q in Fig. 189: or lastly, a beam is placed horizontally from 
one wall to the other,'with the ieet of the rafters let into it, as at 
r r in Fig. 190. This produces the greatest possible strength, for 
now" any tendency that the feet of the rafters may have to spread 
is converted into a horizontal strain upon the beam r r, which 
ties the two feet of the rafters together, and removes all strain 
except weight from the supporting walls. This same cross beam 
by being notched down upon pieces of timber placed longitudinally 
upon the top of each wall, and extending their whole length, also 
answers the purpose of tying the two opposite walls together, and 
preserving their distance asunder. Such a beam is therefore 
very properly called a Tie or Tye beam, and converts the whole 
frame or piece of framing into a triangle r sr. 

965. The triangle is the strongest form that can be produced 
in framing, and is therefore the figure that should always be aim- 
ed at in putting timbers or other beams together where stability 
is the main object to be obtained. This will be readily under- 
stood by inspection of Fig. 191, in which let t v, t w, and w d, re- 
present three slats or strips united together by three common 
screws or nails, one being put at each angle so as to form a tri- 
angle of wood: and it will be found that such triangle will be im- 

66 



522 OF CARPENTRY. 

mutable as to shape or figure; but if any one screw, as that at w 
be withdrawn, then the form of the whole assemblage becomes 
mutable, for the pieces 1 7v and v w will then be capable of re- 
volving in entire circles round the screws at t and v as centres or 
pivots, as marked by dotted lines. But so soon as the screw at w 
is restored to its place, or made to hold the two ends w of the two 
pieces t w and v w together, the assemblage is only capable of 
taking the single immutable form shown in the figure. No change 
can take place at the angle t unless the ends w and v are permit- 
ted to recede from or approach each other, and that is prevented 
by the interposition of the piece w v, supposed to be immutable 
as to length; no change can occur at the angle v, on account of 
the action of the immutable piece i w, and in like manner no 
change can occur at w, by reason of the piece t v; consequently 
so long as the three pieces are incapable of varying in length, the 
figure formed by them will be invariable in form, notwithstand- 
ing the three joints by which they are attached may all be pivots 
upon which any pair of pieces would be free to revolve in circles 
before the third junction or attachment was made. 

966. From this simple principle two of the most important rules 
for the framing of beams or timbers are derived, viz: — 

1st. All timbers united together in a piece of framing should be 
so disposed as to form triangles, having in every place the largest 
or most obtuse angles that the nature of the construction will ad- 
mit of 

2ndly. Precautions must be taken to prevent any of the beams 
or pieces forming the sides of such triangles from bending, or 
otherwise changing their length. 

967. A few examples will show the importance of attending to 
these rules in practice. Thus in the construction of a common 
field gate, as shown in Fig. 192, such gates usually consist of two 
square upright styles or pieces of wood a and 6, with thinner rails 
c and d morticed into them at top and bottom, so as to produce a 
rectangular frame of Vv'ood, hung by iron hinges to the fixed post 
e. The piece a will maintain its position, being supported by the 
hinges; but b will be at least six or eight feet from a, to which it 
is only attached by the rails c and d, or perhaps by another cen- 
tral rail between the two, and as these pieces have considerable 
weight, and great leverage on account of their length, and nothing 
to support them but the strength of the mortices, or other joints, 
at the angles, the end h of the gate will soon sink down in spite of 
any strength of joints, and the whole gate will change its rectan- 
gular shape for the rhomboidal one, shown by the dotted lines in 
the figure, in consequence of which it will drag on the ground and 
be difficult to open. We may attempt to strengthen such a gate 



OP CARPENTRY. 52 



o 



by nailing vertical slats or palings upon the rails, but this will only 
increase the evil by adding more weight to be supported, while all 
the joints being rectangular ones, will admit of turning like the 
pieces that compose a parallel ruler. But if we introduce a trian- 
gle into the frame by using a diagonal bracing piece, as shown at 
a b, Fig. 193, it will be impossible for the end b of the top rail c 
to sink or fall, without producing a sensible compression or dimi- 
nution of the length of the piece a b, which we thus see is a strut 
or beam liable to longitudinal compression. Its strength will also 
support the style b, which will also uphold the bottom rail c/, and 
thus while the joints hold good, no part of such a frame can give 
way from the effects of gravitation or weight. 

968. Ignorant carpenters who know that such a diagonal brace 
is always introduced into a well made gate, but do not consider 
the nature of its action, frequently reverse the proper position of 
the brace, which will be done in Fig. 193, simply by attaching the 
hinges to the style 6 instead of a. The brace will now point 
downwards instead of upwards, and it is now converted into a tye 
instead of a stmt: for in this position it will be subject to a longi- 
tudinal strain of extension instead of compression, and hence its 
place and assistance would be as well supplied by a chain as by a 
stiff bar. As joints can seldom be made as strong as entire timber, 
so in this case the action of the strain will be chiefly felt in the 
joints, which usually give way, and then the frame will droop or 
change figure as readily as if no brace had been applied. 

969. It is of great importance that the rectangular figure given 
to the water gates of canal locks should be correctly preserved, 
therefore precautions are always taken in their construction to 
insure this effect. Fig. 194 represents one of these gates. They 
usually consist of two upright posts e andy*,/ called the quoin or 
hanging post, and e the mitre or shutting post, both made of large 
and strong square timber, united together by horizontal rails or 
cross timbers morticed into them, as at ^ ^ ^ ^', and i is the bottom 
iron pivot or gudgeon upon which the gate turns, the upper part 
of the quoin post being kept in its proper vertical position W a 
strap of flat iron that surrounds it, as at k; lastly this frame is 
covered with two inch oak, or other sufficiently strong plank mm, 
closely jointed, to prevent the passage of any water. Such a gate 
must of course be very heavy, and as its bottom rail g' moves very 
nearly in contact with the bottom or floor of the lock, if the gate 
should loose its square shape by the mitre post e sinking down, 
the bottom would drag upon the floor, and prevent the possibility 
of opening or shutting it. It is moreover exposed to another in- 
convenience, viz: that the whole gate is sometimes nearly covered 
by water, and occasionally left dry; and as nearly all timber is 



524 OP CARPENTRY. , 

lighter than water, the gate will be lifted or borne upwards from 
its tendency to float when covered with water, or will hang with 
its full weight when dry. Such gates, from their weight, require 
considerable force to move them, and a lever becomes necessary 
for that purpose, and that lever is made to answer the double pur- 
pose of affording power to move the gate, and to balance it upon 
its posts. It is therefore called the balance beam, and is usually 
formed out of an entire stem of a tree, squared only near its top, and 
left round, or of the full size, at the root or lower end. It is fixed 
as at n U the end n being morticed into the inner side of the mitre 
post, while the quoin post mortices into it, and the tail or heavy 
butt end / projects over the land at the side of the lock, thus an- 
swering the purpose of a lever for moving the gate, and at the 
same time balancing or nearly balancing the weight of the gate 
to which it is adjusted, by adding iron weights near the end l, 
should it not be heavy enough, or cutting away a part of the tim- 
ber should it be too heavy. In this way, therefore, the gate may 
be so balanced and supported as to destroy any tendency it might 
have to sink and drag, therefore the planking is very frequently 
nailed in vertical directions upon the rails, but the writer prefers 
fixing it diagonally, as shown at m m in the figure, because then 
the planks become so many diagonal braces which render the gate 
much stiffer and less capable of changing its figure. 

970. In constructing square framed buildings the usual mode of 
proceeding is to prepare four sills, in the first instance, of lengths 
correspondent to the size of the intended erection. These sills are 
morticed on their upper side to receive tenons or tongues to be 
formed on the lower ends of the angle posts and intermediate studs 
or quartering. The mortice holes being made, the sill is bedded 
in mortar upon a brick or stone foundation made level, and pre- 
pared to receive it, as at Fig. 195, in which o is the sill with the 
studs and angle posts put in their proper places, their upper ends 
being likewise morticed into an upper horizontal piece of timber 
p, in this case called a plate or capping piece, the use of which is to 
hold the several vertical pieces together in their proper parallel 
positions. If, however, all the studs and angle pieces are parallel 
to each other, and at right angles to the sill and plate, so as to 
form a series of rectangular openings, there will be no strength or 
stability in the erection, for a gust of wind, or any small force ap- 
plied against the side of such a building, even when covered with 
boarding, would drive all the studs and upright pieces out of their 
perpendicular positions, which done, they would have no strength 
or support beyond what the morticed joints could aflford them, and 
the whole building would probably fall. But if only two diagonal 
braces are applied to the opposite sides of the central studs alone, 



OP CARPENTRY. 525 

on each side of the building, in the form shown by the dotted lines 
at r and 5, triangles will be introduced into the frames, and with 
them stability will be produced; for now the central stud can nei- 
ther move towards r or s, and as that cannot move, so likewise the 
plate JO will be incapable of moving, and as all the studs are mor- 
ticed into this plate, so general stability is produced to the whole, 
by merely giving stability to a single post or stud. 

971. This arrangement is not always convenient, because it may 
interfere with a door that may be required in the centre of the 
building, nor will it afford such effectual assistance as if more 
diagonal braces were used. But so long as the principle is pre- 
served, it matters not how the braces are disposed, so that they 
are kept as long as possible, and all acute angles in their positions 
are avoided. A B and C, Fig. 196, exhibit three forms in which 
diagonal braces may be disposed in framed work without inter- 
fering with doors or windows, the studs being shown by single lines, 
and the sills, angle posts, and plates by double ones. In A the 
braces extend up to the plate and meet in a point abutting against 
each other, by which the greatest length of brace or largest trian- 
gle is produced. In B the angle posts only are braced, without 
any of the intermediate studs; and in C the angle posts and a mid- 
dle post are braced, as well as the plate, in order to produce greater 
strength for an upper story, or heavy roof. 

97.2. It has been already stated (966) that to produce the 
strongest framing, triangles must not only be formed, but care 
must be taken to prevent any of the pieces forming the sides of 
such triangles, (and especially that side that is to become the 
brace,) from bending or otherwise varying in length. Timber is 
not much subject to vary in length from natural causes, therefore 
the great point to be attended to, is to keep the pieces from bend- 
ing or changing figure, a defect they will be subject to, even from 
their own weight, if long, but which is very effectually resisted by 
the position of the studs; for when diagonal braces are used, the 
studs do not run in one length from top to bottom by the sides of 
such studs, but are cut off to the bevel or diagonal of the braces, 
and are nailed to them both above and below; being thus brought 
into the same plane with the braces themselves, they, very effectu- 
ally, preventing their bending. This is, at the same time, an 
economical process as regards timber, since many short pieces, 
and pieces of various lengths can be brought into use, which would 
otherwise be useless. 

973. The effects of bending to be guarded against seldom occur 
in small constructions, in which any required degree of strength 
and stiffness can be obtained, but only in large erections where the 
timbers are very long and heavy, and consequently liable to swag 



526 OF CARPENTRY. 

or bend by their own weight, or the loads placed upon them. 
Thus in the triangular roof shown at Fig. 190, we may imagine 
the tye beam r r to be so long, that instead of preserving its right 
lined form, it may sink or swag into the curved form indicated by 
the dotted lines in the figure. A pillar or prop, such as would pre- 
vent this effect, if placed under the centre of the beam, might be 
detrimental to the room below, and is therefore inadmissible; but 
in its place we may substitute the Y shaped iron rod, shown at s 
t, in the figure, so formed that the upper arms of the Y may either 
pass through, or hook over, the upper ends of the two rafters r 5, 
while its lower end passes through the centre of the tye beam, and 
terminates in a screw^ and nut at t, by the turning of which that 
beam may be drawn upwards, and be restored to its original 
straight form. The weight of the central part of the beam will 
thus be thrown upon the two rafters r s,r s, being thus converted 
from a perpendicular into an oblique strain; and if these rafters are 
sufficiently strong and stiff to bear the load without bending, there 
need be no doubt of the stability of the construction, which would 
now be called a truss or framed truss. The iron tye just spoken 
of, is of such vast importance in the framing of trusses, or construc- 
tion of trussed roofs, that it is by way of distinction called a king 
post, and although here spoken of as being formed of iron, is much 
more frequently made of wood; although several instances have 
occurred of large roofs being constructed with iron king posts. 

974. We may, however, suppose the roof to be so large that 
the rafters r s must be so long as to be incapable of supporting 
their own weight without swagging, and giving a concave surface 
to the covering of the roof, and in such a case this construction 
must not be relied upon, but supporting aid must be given to the 
central parts of the rafters; and this is most commonly done by 
oblique struts from near the bottom of the king post, placed so as 
to be nearly perpendicular to the direction of the rafters, as 
shown by Fig. 197, in which a is the tye beam, b b the rafters, 
and c d 3, timber king post. The feet or bottoms of the rafters 
are let into the tye beam by proper mortices and tenons to be 
hereafter described; and this letting in does not take place at the 
extreme ends of such tye beam, but at such distance from them 
as will prevent the lateral strain of the rafters from pushing 
away the portion of wood that resists their pressure. The tops 
of the rafters, it will be seen, do not touch or abut against each 
other, but are let into shoulders cut out of the king post, near its 
top c, in such a direction as to be at right angles with the length 
of the rafters, while the bottom of the king post is morticed 
through the centre of the tye beam. The struts b d, b d, for sus- 
taining the rafters are inserted, as nearly as may be, under the 



OF CARPENTRY. 527 

middle of their lengths, and the lower ends of these struts rest 
upon shoulders cut out near the bottom of the king post at d, such 
shoulders being made at right angles to the direction of the struts. 
The king post is always made broader than it is deep, in order to 
admit of the formation of these shoulders without becoming too 
much weakened. It might be formed of a rectangular piece of 
timber, or one that is flat on all its four sides, as indicated by the 
dotted lines in the figure; but as this would add greatly to the 
weight of the piece, it is customary to cut king posts into the form 
drawn in the figure, which leaves ample strength with diminished 
weight; and lightness is an object which should be sought in the 
construction of every roof. The back and front of the king post 
are, however, left flat and parallel, and its thickness is usually the 
same as the width of the tye beam to which it is attached. 

975. A truss, such as has been described, fulfils every condition of 
strength and stiflTness that can be required in a roof not exceeding 
a span of twenty or thirty ieet, provided the size of the timbers 
are well proportioned to each other, and the joints are well and 
securely made; for the tye beam cannot sink in its centre, being 
upheld by the king post. The king post is upheld by the rafters, 
and they are prevented from bending or changing figure by the 
struts, consequently the entire weight of this truss (with the ex- 
ception of the two halves of the tye beam) is relieved, or changed 
from lateral into longitudinal condensing pressure. The great 
points to be attended to in the construction of this truss, are the 
security of the joints at the feet of the rafters, which are assisted 
by their own weight, and the attachment of the bottom of the 
king post to the centre of the tye beam at d, which is weakened 
by the weight of the tye beam, and therefore requires great care. 
This joint, instead of being made a common mortice and tenon pin- 
ned together, is usually further secured by a strap of flat bar 
iron, so bent as to pass under the tye beam and up the two sides 
of the king post, to which it is firmly spiked or nailed. 

976. It may appear that the diagram of the roof given in Fig. 
197, does not accord with the form in which roofs are generally 
seen, on account of the feet of the rafters being placed a consider- 
able distance within the tye beam, so as to leave breaks or flat 
places at e e, while the shingling, slating, or other covering of a 
roof generally oversails or projects beyond the perpendicular 
range of the external walls, so as to throw rain water some dis- 
tance from them, as shown by the dotted line f. This difference 
of form arises from the whole roof not being constructed in the 
manner described; for that would render roofs too heavy, expen- 
sive, and unnecessarily strong. The truss that has been described 
may be called the back-bone or support of the roof, instead of the 



528 OF CARPENTKY. 

roof itself, which is generally a very light construction, indepen- 
dent of, but supported and upheld by these trusses, which, on this 
account, are called the principals or trussed principals of the roof, 
and they are therefore few in number, and are usually placed at 
from seven to ten feet asunder, according to the magnitude of the 
building, or the weight of the material with which it is to be 
covered. On this account the timbers which we have called 
rafters should, in fact, be called principal rafters, because they are 
not the rafters of the roof, but the rafters of the framed truss or 
principal that is to support the roof, and by way of distinction, 
the rafters of the roof are always called common rafters, A prin- 
cipal rafter must be a stiff and strong piece of timber, cut thicker 
at its lower than at its upper end, because the load near the ridge 
of a roof is less than near its base; while common rafters are 
parallel, or of the same size from one end to the other, and are 
usually made of common quartering, or scantling of 4 by 2^ 
inches square. A very common method of preparing principal 
rafters is, to select a whole stick of die square timber, suppose of 
10 by 12 inches square, and long enough to make one, two, or 
any given number of rafters without waste. It is then slit or saw- 
ed through the middle of its length into two pieces, say of 12 
inches wide by 5 inches thick, and being cut into proper lengths 
for rafters, one oblique cut is made through the flat side as in Fig. 
198, by dividing the two ends of the piece, suppose into 7 and 5 
inches, so that two principal rafters are produced at once, with- 
out waste of timber, 5 inches thick, but with the lower ends 7 
inches deep, while the upper ends are but 5 inches square. 

977. The form of truss for the principal, having been decided 
upon, the actual roof is built upon it by means of what are called 
purlins, being long pieces of square timber placed in horizontal 
directions at equal distances apart along the upper surfaces of the 
principal rafters, as shown at^^ in Fig. 199, which only exhibits 
a transverse section, or end view of them. When joints are ne- 
cessary in the length of a purlin, they must always take place 
upon a principal rafter. The purlins project considerably above 
the principal rafters, because these timbers are merely notched 
on to each other to prevent their slipping, being let about half an 
inch into the principal rafters, while the rafters are let about as 
much into them before they are nailed. The purlins being fixed 
the common rafters succeed, and these rest upon the purlins in 
their middle parts, asat^^, while their upper ends are cut bevel, 
so as to fit against the two parallel and vertical sides of an inch 
and a half board, or two inch plank h, called the ridge piece^ that 
is let into notches cut to receive it in the tops or crowns of all the 
king posts. The ridge piece should rise at least three or four 



ROOFS. 529 

inches above the tops of the common rafters when tiles or slates 
are used, in order that they may abut against it, when they are 
covered with a capping of sheet lead or copper nailed and dotted 
(649,) on to the top of the ridge; but with shingles this precaution 
is seldom necessary. The lower ends of the common rafters are cut 
bevel, to fit on to the flat top of a plate or piece of timber called 
a pole plate, which, like the purlin, runs the whole length of the 
building, and is supported on the ends of the tye beams, as at i in 
the tigure, or upon the tye beams and wall between them con- 
jointly; or wholly upon the walls when the tye beams are not 
long enough to carry them. But the tye beam often projects be- 
yond the wall, and affords the means of attaching a cornice under 
the eaves of the roof as at/ in Fig. 197. It sometimes terminates 
within four inches of the outer face of the wall, so as to be cover- 
ed with brick- work, and is thus hidden as at z. Fig. 199, or the 
wall sometimes finishes with a parapet or dwarf wall hiding 
part of the roof, as at I, Fig. 199, in which case the rain that 
falls on the roof is confined, and then gutters of sheet lead or cop- 
per become necessary. Such gutters require a boarded bottom, 
which is supported upon bearers, being small pieces of board nail- 
ed on to the sides of every common rafter as at m, and varying in 
height so as to give the necessary fall or descent to the bottom of 
the gutter, kk k km both the last figures shows a section of the 
wall plate before spoken of (924) as extending along the entire 
length of the top of the wall, and upon which the tye beams are 
corked or halved, in order to make the roof stable in its position, 
to equalise its pressure over the whole length of building, and to 
tic or connect the two exterior walls together. 

978. The common rafters, instead of being merely bevelled and 
nailed down at their feet as at i, Fig. 199, are very frequently 
hird^s mouthed on to the pole plate, or cut into the form of a notch, 
such as is shown at Fig. 200, in which a is part of the side of a 
rafter, and h a section of the pole plate on which it abuts, and to 
which it is nailed down. This effectually prevents the rafters 
slipping away and getting out of their places at their feet. To 
render rafters more secure they should also be notched or halved 
on to the purlins. All rafters should be in single pieces, if possible, 
and every joint of a rafter (if joints are necessary,) must be upon 
a purlin. 

979. Fig 201 shows a side view or elevation of a naked roof , 
such as has been described. The term naked is applied to all 
roofs, floors, partitions and other pieces of framing that are in- 
tended to be covered with boards, shingles, lath and plaster, or 
other covering, before such covering is put on. The end A of 
this roof shows the termination of a square or common span roof 

67 



530 OF CARPENTRY. 

over the pediment or gable end of a building, in which the bricks 
or other materials of the wall are ramped to suit the rake or 
angle of the roof, consequently no framed principal is here neces- 
sary, but the ridge piece A, purlins g g, and pole plate i, are all 
supported in their proper places by the brick-work at A. The 
end B, on the contrary, shows the termination of a hipped roof, or 
that which is placed over a building, the walls of which do not 
rise into a gable, but terminate in horizontal courses, and then 
the end of the roof has the same slope or inclination as its sides, 
and it is bounded by two sharp edges or ridges which meet to- 
gether at the common top or ridge, and are called the hips of the 
roof; while if two portions of roof meet and intersect each other 
at right angles, as is very commonly the case, a hollow or concave 
angle will be produced, and that is called a valley. 

The shaded lines at A: and I show the positions of the principals 
within the roof, and a a are the ends of the two tye beams upon 
which they are framed. One of these framed principals must be 
placed under the intersection of the hips and the plain roof, as at 
2, and the other may be placed in any convenient position; but 
the usual method is to divide the whole length of the straight roof 
into equal parts of from six to nine feet each, and to put a princi- 
pal truss under each. The further they are set apart, and the 
stronger the purlins must be, since the whole weight of the exte- 
rior roof rests upon them, and the whole weight of the entire roof 
uponlthe principals. It is not at all essential that a principal 
shou d come under a common rafter, therefore no attention need 
be paid to their respective positions. ^ g in the figure show the 
common rafters placed over the purlins and resting at their tops 
against the ridge piece h, and at their bottoms upon the foot or 
pole plate i. These rafters are all of the same size from top to 
bottom, as well as in respect to each other, and they should be 
placed at fifteen inches from centre to centre, or one foot in the 
clear from each other, when the tiles, shingles, or other covering 
is fixed upon laths, or small slats nailed horizontally upon the 
rafters; but if they are covered with inch boards, which is always 
the case when a roof is slated, and frequently when it is shingled, 
the rafters may be put eighteen inches or even two feet apart. 
The short rafters that occur in hips like those near B are called 
Jack Rafters. 

980. The roof is finished by nailing slates or shingles upon the 
boarding or laths above described, in doing which care must be 
taken that no two joints occur over each other. The operation 
commences from the eaves or lower edge of the roof, where two 
courses of covering are always necessary, in order that the up and 
down joints of the first course may be covered by the middle of 



ROOFS. 531 

the plates that form the second; afterwards in proceeding up- 
wards only one course is necessary, because all slates, shingles, or 
other plates used for covering, should be so long as to reach more 
than half way under those that are placed above them. The 
length of the plate or shingle therefore regulates what is called 
the gauge of the roofing, that is the distance between the lower 
edge of any one plate, and of that which is next above it. Thus 
shingles are said to be put on to a 5, 6, or 7 inch gauge, meaning 
the distance between one horizontal range and another, or the 
length of shingle that is exposed to view. Slates are frequently 
so large as to admit of a 10 or 12 inch gauge, or even more.* 
The tiles that are used in England, whether plain or pantile (490) 
require no boarding, but are constantly laid upon strong laths 
called double fir laths, or pantile laths, without nails. Shingles 
are fixed by nails, called shingling nails, and the operation is per- 
formed by the carpenter; while tiling, on the contrary, is the work 
of the bricklayer. Slates, from their being thin and brittle, re- 
quire a certain degree of skill in the cutting, making the nail 
holes, and laying, so as to prevent waste, and on this account their 
use is considered a separate branch of business in England, and is 
performed by the slater. Iron nails are used to fix shingles, and 
endure as long as the shingles will last; but as good slates may be 
considered everlasting, (unless broken or injured by accident,) 
they ought to be fixed with copper nails, that do riot rust away. 
Roofs are occasionally covered with sheet lead, copper, or zinc, 
in all which cases they must be covered with planed boarding, 
and the long joints in the metal should be vertical, and not solder- 
ed, but so constructed as to admit of expansion and contraction 
(648). 

981. The building may be so extensive that the form of trussed 
principal, shown in Fig. 197, may be insufficient; because cases fre- 
quently arise in which the tye beam may have such a great length, 
that although supported in its middle, it may swag at both ends 
between the middle and the walls; or the principal rafters may 

* In England where slates are very generally used for covering the best build- 
ings, they are split and cut at the quarry into square plates, and are sold and dis- 
tinguished by the following singular names, depending on their quality and size. 

Doubles, are - 

Ladies, 

Countess's, ------ 

Dutchess's ------ 

Glueen's, (also called Rags,) - - - 

Imperials and Patent, - - - . 
They are sold by the 100. The quantity necessary to cover a square of roofing 
of the first four kinds will weigh from 6 to 7 cwt. The large slates being also thicker 
will weigh from 7 cv't. to a ton. The word Patent applies to the mode of fixing 
and not to the slate. 



1 ft. 


2 inches by 6 


1 „ 


3 „ byO 8 


1 „ 


10 „ byO 11 


2„ 


2 „ by! 3 


3„ 


3 „ by 2 3 


a„ 


8 „ by 2 2 



532 OF CARPENTRY. 

be so long as to be incapable of being supported by a single brace 
or strut. This last evil may be remedied by dividing the length 
of the rafter into three instead of two parts, and applying two 
struts on each side of the king post, instead of a single one, but 
this will not relieve the tye beam, therefore another form of truss 
must be resorted to, and such a one is shown at Fig. 199, and is 
called a truss with king and queen posts. 

In this truss all the same parts occur as in Fig. 197, with the 
addition of the two queen postspjo and their extra struts rr. The 
king post is formed and placed as before, but its struts s s instead 
of bearing up the rafter immediately, bear under shoulders form- 
ed on the upper part of one side of each queen postjop, and thus 
effectually prevent them from sinking, while the lower ends of the 
queen posts being morticed into, and firmly attached to the tye 
beam at that part where it stands most in need of support, main^ 
tains it in its place, and a pair of secondary or queen struts r r 
being applied from shoulders near the bottoms of the queen posts, 
support the lower portion of the rafters. Such a principal truss 
will, therefore, be competent to the support of a roof having a 
span or distance between the external walls of from 30 to 40 ieet. 

982. Such are the general principles upon which all roofs are 
constructed, and the two examples given are the forms that are 
generally used; but the form admits of many modifications, and as 
these principles of roof construction run through most of the varie- 
ties of heavy framing, such as the construction of wooden bridges, 
the centring upon which stone arches are built, and many other 
cases, we shall enlarge upon this subject, in order to render the 
others more simple and intelligible, when they come under con- 
sideration. 

983. Thus, for example, a considerable saving of timber will be 
produced in a roof not exceeding 30 feet span by leaving out the 
king post and its struts, as shown in Fig. 199, and supporting the 
tye beam in two, instead of three places by using the queen posts 
only with a straining beam between them, as shown by Fig, 
202. All the principal timbers in this design, are likewise much 
shorter than in those that preceded, and this is frequently a de- 
sirable object. The principal rafters 1 1, for example, instead of 
proceeding up to the ridge of the roof stop short and abut against 
shoulders near the tops of the queen posts, and instead of abutting 
against each other or against the ridge piece, they transfer their 
pressure to the horizontal beam i?, in this case called a straining 
beam, and the rafters are stiffened and supported near their cen- 
tres by the oblique struts at 1 1, which take their bearings against 
the feet of the queen posts. One purlin is placed over each strut, 
and another is supported on the top of each queen post. Upon 



ROOFS. 533 

these the common rafters are placed as before, but they run up 
to the ridge piece against which they abut and are nailed. In 
this roof, its weight is converted into a compressing force tending 
to shorten the two principal rafters, and the straining piece; and 
should any apprehension exist of the latter bending under the 
force exerted, it may be stiffened and assisted by a single stud, 
fixed as dotted in at u. The feet of the struts t t may also press 
so strongly against the feet of the queen posts as to endanger the 
breaking off of the tenons by which they are attached to the tye 
beam; but this difficulty will be met by introducing a beam called 
a straining sill, as at w, driven tightly in between the two queen 
posts. Neither of these latter expedients were, however, thought 
necessary in the roof from which this drawing was taken, and 
which was constructed by the celebrated Smeaton over a water 
mill on the Ravensbourne river at Deptford, near London. 

984. The roof of the Chapel of the Royal Naval Hospital at 
Greenwich, near London, which was designed by Mr. Samuel 
Wyatt, is an excellent example of a roof on this construction, and 
as it has stood a number of years without any symptoms of change 
of figure, and has been much admired for its simplicity as a piece 
of carpentry, we have given a representation of one of its trussed 
principals in Fig. 203, and shall subjoin the scantlings or sizes of 
the timbers made use of in its construction. One peculiarity 
of this roof is, its nearly flat top, which is an advantage when 
it is not desirable to show a high roof above a building. In the 
last century a fashion or mode of building existed, in which most 
enormous roofs (frequently nearly as high as the perpendicular 
building) were exposed to view; while now the custom is to con- 
ceal the roof, either entirely, or to a great extent. This roof is 
likewise without common rafters, which become unnecessary, 
because the whole of it is covered with sheet lead. This permits 
i\\e pitch, or central elevation, to be lower than is usual in roofs; 
for if the directions of the rafters should be carried up until they 
meet at the point i, the height of this point above the tye beam 
a a would only be equal to one-fourth of its length, instead of one- 
third, as is usual in tiled or shingled roofs. The trussed principals 
are set 7 {QQi apart, and parallel to each other; and in lieu of com- 
mon rafters a number of small purlins or horizontal bearers, each 
6 inches deep and 4 inches wide, are fixed at 1 foot asunder, as 
shown in the drawing, and upon these, boards with vertical joints 
are nailed to support the lead. 

Inches. 
a a, Is the tye beam 57 feet long, (the clear span between 

the walls being 51 feet,) its scantling is, - - 14 by 12 



Inches. 


9 


by 12 


9 


X 7 


10 


X 7 


6 


X 7 


10 


X 7 


9 


X 7 


2 


X 2 


6 


X 4 



534 OF CARPENTRY. 

c c, Queen posts, - - - - - 

t/, Struts or braces, - - - - - 

e, Straining beam, 

f, Straining piece to receive the struts, - - - 
gf Principal rafters, --.-.- 
k, A cambered, or bent piece to produce weather on the 
platform, ------- 

6, An iron screw bolt to support the tye beam, 

The horizontal ledgers for supporting the boarding are. 

This is a beautiful roof, and contains less timber than most 
others of similar dimensions. The parts are universally admitted 
to be well proportioned and disposed. It has been thought that 
the iron screw bolt is unnecessary, but it adds great stiffness to 
the whole. 

985. The roof of the Theatre, in the great manufacturing town 
of Birmingham, in England, designed and executed by Mr. George 
Saunders, of London, is generally admitted to be one of the boldest 
and lightest roofs in Europe, and has been much extolled as a fine 
specimen of carpentry, for which reasons the construction of one 
of its principal trusses is given in Fig. 204. The clear span of this 
roof, or distance between the supporting walls, is 80 feet, <ind the 
principals are set 10 feet apart; but oak corbels, 9 by 5 inches 
square, shown at a a in the figure, are built into the wall at every 
five feet for the purpose of giving support to an inner plate or 
string of timber 9 inches square, which runs along the whole in- 
side of the wall, as shown at 6, to assist in supporting the tye beams 
and the roof, which also rests upon the usual wall plate c, being 
8 inches by 5j square. The scantlings of the timbers of this roof 
are as follow: — 



df The pole plate, - - - 

e, Tye beam, ------- 

f, Straining beam, -_.--• 

gy Principal queen posts, in the shaft, or exclusive of the 

projecting shoulders, ----- 
h. Minor or secondary queen posts, (in the shaft,) 

i, Principal rafters, 

k. Common rafters, ------ 

/, Principal struts or braces, - - - - 

m, Secondary do . - . . - 

w, Purhns, ------- 

q, Straining sill, (bolted down to tye beams,) 

5, Ridge piece, 





Inches. 


7 


by 5 


15 


X 15 


12 


X 9 


9 


X 9 


9 


X 7 


9 


X 9 


4 


X 21 


9 


X 9 


9 


X 6 


7 


X 5 


9 


X 5i- 


9 


X 5i 



ROOFS. 535 

In this roof the straining sill q gives a firm abutment to the 
principal braces, and as the length of this piece is 19j feet, that 
being the distance between the principal queen posts, it affords 
roomy work shops, extending the whole length of the building, 
and lighted by sky-lights for the carpenters and other workmen 
connected with a theatre. There is also a beam on each side, 
bolted to all the tye beams as at r, the intention of which is to 
prevent the total failure of so bold a trussing, if any of the tye 
beams should fail at the ends by rot. This is further guarded 
against by the introduction of the internal plate h supported on 
corbels: because experience shows that no part of a roof is so 
likely to give way as the ends of tye beams bedded in the walls 
(665,) where they are deprived of a free circulation of air, and 
are often exposed to confined humidity from the leaking of rain 
water, from condensed vapour running down the inside of the roof, 
or from imperfections of the gutters. 

986. The roof of Drury Lane Theatre in London, is, however, 
allowed to be, perhaps, without equal in the world for lightness, 
stiffness and strength, and we shall therefore close our account of 
large roofs by giving a table of the' scantlings of its timbers, the 
disposition of which is shown by Fig. 205. This beautiful struc- 
ture was designed by Mr. Edward Grey Saunders, an Architect 
of London, and brother to the designer of the last described roof 
The span between the walls is 80 feet 3 inches, and the princi- 
pal trusses are 15 {eet apart. The main beams, which are of fir, 
are trussed in the middle space by oak trusses 5 inches square, an 
operation that has not yet been described, but will shortly come 
under consideration. (See 1022.) This became necessary on ac- 
count of the great width that was required for workshops, the cen- 
tral opening being 32 feet wide. At the same time the great distance 
of the trusses from each other, and the peculiar form of the roof, 
permitted many large rooms to be constructed on each side, with 
flat ceilings and vertical windows through the walls instead of 
sky-lights, and yet without any interference of the timbers of the 
roof, which were wholly concealed in the partitions between one 
room and another. The main trusses are so judiciously framed 
that it was computed that each would safely sustain a load of 
300 tons, and the division of the whole into three parts, caused 
the real or exterior roofing to be very light. The strains are ad- 
mirably kept from the side walls, which are even firmly bound 
together by the introduction of what may be called two sets of 
tye beams, one above the other. The following were the scant- 
lings made use of. 

Inches. 
a a a. Three separate tye beams for the upper, or ex- 
ternal roof, each - - - 10 by 7 



7 


X 


5 


9 


X 


5 


10 


X 


3 


5 


X 


5 


12 


X 


6 


5 


X 4 


15 


X 


12 


12 


X 


12 


12 


X 


8 


12 


X 


12 



536 OF CARPENTRY. 

Inches. 
6, Principal rafters of the upper roof, - - 7 by 7 

c, Three kings of ditto (full measure including shoulders,) 12 x 7 
dj Struts of ditto, - - _ - 

e, Purlins, - - - - - 

f. Ridge pieces, - - - 

g, Pole plates, - - - _ . 
A, Gutter plates framed into the beams, 
i, Common rafters, . _ . > 
k, Scarfed tye beam to the main truss, which is trussed 

in its central division, _ . - 

m. Principal braces to ditto 14 by 12 at bottom dimin- 
ishing; to - - - - - 
n, Struts to the braces, - . - 
p, Straining beam, - . . - 

The main tye beam k, instead of resting upon the wall plate 
as usual, is caulked or notched down upon a double parallel pair 
of plates running the whole length of the building; and instead of 
this bearing upon the wall, it rests upon the ends of two vertical 
timbers built into the walls, and bearing on long templates be- 
neath. The principal braces m m, terminate so far short of the 
inside walls as to allow room for horizontal beam.s x x, which con- 
nect one principal truss with another, and upon these vertical 
timbers z z^ 10 by 7 inches square, stand to support an internal 
plate y y for supporting the outer ends of the tye beams a a, and 
thus relieve the thin upper w^alls from a great part of the pres- 
sure they would otherwise be subject to. The pieces z z, and 
inner plates y y, are similar in use and effect to the inner plate 
and corbels of the Birmingham roof, but much more effective in 
construction, because the pieces z z have a much firmer bearing. 
The windows for lighting the side rooms are placed in the upright 
walls between the pieces z z, and the side walls rise in coped 
parapets so far above the springing of the upper roof, as to en- 
tirely conceal it from spectators in the streets below. This thea- 
tre was entirely destroyed by fire, and has been rebuilt. The 
present roof varies very little from that of Birmingham Theatre, 
above described. 

987. A very common expedient in the building of houses or 
other erections in v^'hich it is desirable to conceal, or nearly con- 
ceal the roof, is to give it a form similar to the upper part of 
Drury Lane roof, or more frequently to divide the opening into 
two equal parts, with a ridge over the centre of each, when the 
roof, from its peculiar form, is called an M roof. In this case a 
girder is necessary to bear up the middle of the M, which is 



ROOFS. 537 

formed of two simple span roofs, with a gutter of metal between 
them. 

988. Roofs are sometimes extended to very large spans with- 
out columns or supporters of any kind under them, but such are 
not often required. The largest roof ever executed was that of 
the Riding House built at Moscow, in Russia, in 1790, by the 
Emperor Paul I. The span was 235 ieet, and the slope of the 
roof but 19 degrees. The principal support of this immense truss 
consisted in an arch formed of curved pieces of timber indented or 
joggled together (8.55) in three thicknesses, strapped and securely 
bolted together with iron. The principal rafters and tye beams 
were supported by several vertical pieces notched to the curved 
rib, the whole being stiffened by diagonal braces. The disposi- 
tion of the parts of this roof is extremely ingenious, but it was 
made of scantlings too slight for the immense extent of its span, 
and it settled so much as to be deemed unsafe. A further account 
of this roof, with a large engraving of its form and construction, 
will be found in Tredgold's elementary principles of carpentry, 
American edition of 1837. 

989. Another very bold, and at the same time simple mode of 
roofing is that devised by Sir Robert Seppings, Surveyor of the 
British Navy, for covering ships of war while building or repair- 
ing in the dock slips. These roofs are framed from whole timber 
disposed as in the common king post truss. Fig. 197; but so form- 
ed that the two halves of what would be the tye beam in such a 
roof, are made to serve as, or become the principal rafters on one 
side of another pair of similar trusses, built at each of its ends in 
continuation of its length. Such roofs have been constructed at 
Plymouth, Deptford and Chatham dock yards, with a clear span 
of from 90 to 110 feet, and covering a space 150 feet wide. An 
engraved representation, with a description of this kind of roof, 
applicable to covering all large spans for other besides naval pur- 
poses, will be found under the article ''Dock," in the supplement 
to the 4th and 5th editions of the Encyclopedia Britannica. 

990. Notwithstanding the great advantage derivable not only 
to roofs, but to the buildings they cover, from the use of tye 
beams, there are cases in w^hich they are inadmissible without 
great loss of room, at least in height. Thus it may be necessary 
to give the ceiling or covering of a room an arched or coved form, 
the curve of which might rise into the angle of the roof, but can- 
not do so on account of the interposition of the tye beams. The 
curve must therefore be formed wholly below such beams, or else 
they must be dispensed with. One method frequently resorted 
to for getting height in the angular span of the roof is shown at 
Fig. 206, Plate VII., in which a b and c b are the two principal 

68 



538 OF CARPENTRY. 

rafters without a tye beam, the place of which is attempted to be 
supplied by the two oblique tyes a d and c d, which cross and 
halve into each other at e. This may appear efficient, but is at 
the same time a bad form of framing. The natural tendency of 
all rafters is to sink or swag in their middle parts d d, and here, 
consequently, they require support. The oblique tyes are secure- 
ly fixed to the foot of one rafter and the centre of the opposite 
one, and as the natural spread of the roof will constantly draw 
upon the tyes, that draught is transferred to the centre of the 
rafters, which, instead of being supported in their middles, will 
be forcibly drawn inwards and downwards, and as the angles b a 
d and bed are very acute, a strain similar to that described in 
the latter part of paragraph 960, and illustrated by the dotted 
lines in Fig. 187, will be produced. The tyes will also be liable 
to break olf at e, where they are weakened by being halved into 
each other; because if the roof spreads at all, the line a e c will 
be drawn nearer into the direction of a right line, to prevent 
which, it will be obvious that the points b and e ought to be tyed 
or connected together. 

991. By the introduction of a king post this truss may be mate- 
rially improved, as shown by Fig 207, which is one of the principals 
designed by the writer, and used in the additional part of Jefferson 
Medical College, before referred to (942). In this a king post f 
is introduced, having a nearly horizontal strut g on each of its 
sides so as to appear like a collar beam, but which is intended to 
resist compression, instead of acting as a tye, its object being to 
maintain the king post in a vertical position, and at the same time 
to give some support to the central part of the rafters, the upper 
halves of which are sustained by the shorter oblique braces, 
which also abut against the king post higher up. The long 
oblique tyes are fastened to the feet of the rafters as before, but 
instead of proceeding to the opposite rafter they stop short a little 
beyond the bottom of the king post, to which they are notched or 
joggled, one on the one side, and the other on the other, and then 
bolted through, and iron strapped together. The equal straining 
forces of these tyes being thus transferred to the two opposite 
sides of the king post will draw in opposite directions and neutral- 
ize each other, and they cannot descend towards a right line, 
being supported by the king post. The true regular curve of the 
ceiling is obtained by blocking out, that is, nailing longitudinal 
scantlings of such different sizes as may be required to the under- 
sides of the oblique tyes for the purpose of obtaining the exact 
curve required, and for receiving the laths and plastering with 
which the ceiling is to be finished. 

992. Before proceeding to describe other applications of car- 



JOINING TIMBERS. 539 

pentry, it will be convenient to say something in this place on the 
manner of joining; timbers together, on the iron work necessary 
to assist such joints, and on the process of trussing beams to give 
them greater stiffness. 

It will be quite obvious that in the construction of such large 
roofs as have been already described, no timber can be procured 
of sufficient length in single pieces to form the tye beams and 
other extended parts, consequently two or more sticks of timber 
must be united together by their ends, or in the direction of their 
length, and this operation is called scarfing timber, and is perform- 
ed in various manners. The most common method of scarfing or 
joining beams longitudinally is called lapping or halving, and some- 
times ship lapping timbers. This consists in cutting away a suffi- 
cient quantity of one beam on its upper side, and an equal quan- 
tity of the one that is to be joined to it on the under side, so as to 
let the diminished end of one piece overlap the diminished end of 
the other, and then joining the two together by nails or wooden 
pegs or pins, which in carpentry are called tree-nails, as shown by 
Fig. 208. This kind of joint is constantly used for uniting founda- 
tion sills that are supported upon hard and level foundations, 
bond timbers, wall plates, and the pole plates of roofs, but it would 
not answer for timbers exposed to longitudinal compression or ex- 
tension, especially the latter; because the only strength to resist 
separation in this case is that of the nails or pins. It will, 
however, answer against a strain of compression provided the 
shoulders or vertical joints are made to fit each other very truly, 
and the pieces are fastened together by iron screw bolts and nuts, 
or by square hoops or bands passing round them. 

993. The best scarf against longitudinal extension, as in tye 
beams, is that shown by Fig. 209, where the upper and under beams 
are cut or let into each other in the manner shown in the figure. 
The under beam has a tongue or tenon formed at its extreme end like 
a, with a corresponding notch for its reception in the upper beam, 
and the end of the upper beam is similarly treated in respect to 
the lower one. To permit these tenons to pass into the notches 
provided for them, it is necessary to cut away a portion of the 
intermediate part of the joint at c, equal in length to the sum of 
the length of the tenons, in such manner as to form a square hole 
through the middle of the joining of the two beams, and this is 
afterwards filled up by a piece of oak or hard wood, called a key, 
fitting the hole, and driven tightly into it. The effect of this key 
is to drive the tenons a and h home to their shoulders, and to pre- 
vent the possibility of the pieces separating again. Such a joint 
will be capable of withstanding longitudinal extension, which 
will have the e^Qci of compressing the key laterally, and in order 



540 OP CARPENTRY. 

to enable it to withstand such pressure with the greatest effect, 
the thickness of the key ought to be equal to one-third of the en- 
tire beann. 

994. This scarf wiH also withstand lateral pressure fronn above 
or below, as in floors; but the joint most frequently used for 
this purpose is the oblique one shown at Fig. 210. Its principle 
is the same as that last described, but the joint instead of being 
parallel to the top and bottom, is oblique, and instead of the tenons 
being cut with shoulders, the ends of the pieces fit into angular 
notches from which they cannot withdraw when the key is driven 
into its place. When it is desirable to render the timber stitf 
against a lateral pressure in all directions, the ends of both pieces 
should terminate in angular forms, and be received in angular 
notches, as shown at Fig. 211, which is a view of the top of a beam 
scarfed as in Fig. 210, but with angular terminations. This form 
of scarfing should never be used for pillars, or for resisting a com- 
pressing strain, because the sharp terminations of the uprights will 
act as chisels to split open the notches, and the one side will be 
constantly sliding over and protruding itself beyond the other, 
unless the joint is bound round with iron. 

995. None of the scarfs above described can, however, equal 
the strength of an entire beam, because at least half the timber 
must be cut through in all of them. But they may all be made 
much stronger by long straps of flat iron, fixed to the outsides of 
the joints by screw bolts or screw hoops. The only way of joining 
beams, so as to get the complete strength in timber alone, is by a 
method apparently more clumsy and unsightly, but which is much 
used in ship building, and is called Jishing a beam. It consists in 
applying a long piece of timber, equal in area and size to the 
beams to be joined to one side of the joint, as shown at A in Fig. 
212, or two pieces of half the area, one on each side of the joint, 
as at B in the same figure, such pieces being bolted through, 
hooped, or otherwise securely fixed upon the joint. This joint 
will, of course, withstand longitudinal compression; but if exten- 
sion is required, as in tye beams, the scarfs shown by Figs. 209 
and 210 may be adopted, and they may be fished on one or all 
sides of the joint. In long tye beams where straining sills are in- 
troduced, such sill by being bolted down becomes a most efficient 
fishing to a joint below them. 

996. The union of several pieces of timber in angular or other 
directions, when extension of length is not the object to be obtain- 
ed, is sometimes effected by lapping, but more generally by what 
is called morticing. A mortice joint always consists of two parts, 
viz: a tongue or projection from the end of the piece to be joined, 
which is called the tenoiiy and a hole made through the other 



JOINING TIMBERS. 541 

piece, either on one side or passing entirely through the piece 
called the mortice, or sometinfies the mortice hole, to distinguish it 
from the complete joint which is also called a mortice, and the 
junction is usually secured by driving one or two wooden pins or 
tree-nails transversely through the joint, as shown by Fig. 213, 
where A shows the mortice, and B the tenon formed on two beams 
which are intended to go together in a right angled direction, c c 
being the pins driven into holes bored transversely through the 
morticed piece, and passing through corresponding holes shown on 
the tenon. The mortice has generally a width equal to one-third 
of the thickness of the beam, and ought to be kept as far as possi- 
ble from its end to allow sufficient wood at d to prevent the hole 
splitting out. If it is necessary that the end d, of the one piece, 
should be flush or flat with the outer edge of the other piece, this 
is obtained by making the shoulder e of the tenon B wholly on one 
side, but when this is not essential, a shoulder is left all round the 
tenon; and the mortice hole will be stronger, if it can be made 
considerably within the timber instead of being near its end. 

997. There are different modes of forming and uniting mortice 
joints, varying with the purposes for which they are intended. 
In all of them it is essential that the mortice and tenon shall fit 
each other accurately, or as it is technically called, be without 
shake, meaning ability to move about. The joint shown in Fig. 
213 is very good and effective, where the load or strain to be 
borne is an external pressure upon the outsides of either of the 
beams, but would be unfit for uniting a king post to a tye beam, 
because in that case, the natural tendency of the tye beam is to 
descend in its middle and withdraw itself from the tenon of the 
king post, and the only resistance to such withdrawing would be 
in the strength of the pins, instead of the tenon. The best joint 
for this last purpose, or for all cases where the tendency is to draw 
the tenon out of its hole, is that shown by Fig. 214, in which one 
side of the tenon C of the king post is cut into a sloping or inclin- 
ing direction, and the other left straight with the side of the tim- 
ber. The mortice hole D has a correspondent form given to it, 
but is made so much wider than the tenon, that its broad or lower 
end can just pass into its upper or narrow part. When so intro- 
duced a wooden key/, in Fig. E, (which is a view of the joint 
when put together,) is tightly driven, and this forces the inclined 
side of the tenon against that of the mortice hole, and thus pre- 
vents the possibility of the tenon being withdrawn, so long as the 
key retains its place. In addition to this, pins may be driven 
through the joint, and an iron strap applied round it, when it will 
be impossible for the parts to give way, except by breaking. 

998. Another method of fixing a tenon is by end wedging, as 



542 OF CARPENTRY. 

shown at Fig. 215, which represents the joint put together. The 
tenon g in this case should be long enough to reach quite through 
the mortice hole, and having one or more saw cuts made in it, an 
acute wooden wedge h is drawn into each of them, (frequently 
with glue.) This splits the end of the tenon in a slight degree, not 
sufficiently to injure its strength, if judiciously executed, but to 
spread it out and make it press so forcibly against the sides of the 
mortice hole, that it cannot readily be withdrawn, and if the mor- 
tice hole is made a trifle wider next the wedged end, than at the 
other, the tenon will be very effectually fixed. In the construc- 
tion of machinery, it is not always possible to carry the tenon 
through the piece, so as to wedge it on the opposite side, and then 
nearly the same effect can be produced by what is called yba:-^<zi/ 
wedging. In this the mortice hole (which should spread laterally 
as it descends) is not cut through the piece but stops short of the 
opposite side, as in Fig. 210, and the tenon i being made to fit the 
mouth of the hole very neatly, two saw cuts are made in it; and 
two wedges are put slightly into them, when the piece carrying 
the tenon is driven by a mallet into the mortice hole, and the 
heads of the wedges coming into contact with its bottom, are 
driven into the tenon and cause it to spread, as it is introduced into 
its place. Such a joint, if neatly made and put together with glue, 
will be as strong as solid wood. Tenons are very frequently made 
w^ith two or more tongues, and a corresponding number of mor- 
tice holes to distribute the strength of the joints over a large sur- 
face. Indeed dovetailing, which is so extensively used for uniting 
the angles of boxes by cabinetmakers, and for larger constructions 
by millwrights, is closely allied to morticing and tenoning. 

999. In pinning mortices together, the tenon should be driven 
into its mortice hole as far as it will go before the pin holes are 
bored, and then they must not be carried through the joints, but 
merely down to the tenon, so as to mark it, when it ought to be 
withdrawn and the holes be continued through the other cheek of 
the mortice. The holes are then made through the tenon, not 
exactly where they have been marked, but each about one-eighth 
of an inch nearer to the shoulder of the tenon. The effect of this 
will be that in putting the joint together, as the two holes do not 
exactly coincide, driving in the pins will draw the shoulder of the 
tenon close and with great force against the side of the piece to 
which it is to be connected, and will thus produce a closer and 
stronger joint than could otherwise be obtained. 

1000. The mortice joints that require the greatest care and 
attention are, however, those that are oblique, and subject to 
great strains, as in uniting the foot of a principal rafter to a tye 
beam. In such joints the thrust is not only an oblique one of im- 



JOINING TIMBERS. 543 

mense force, but it comes into operation very near the end of the 
beam, where there is sometimes not sufficient timber to resist its 
action. At first sight it may appear that letting the whole foot 
or lowA end of the rafter into the tye beam would produce the 
most effective joint, but in this way the whole surface of the rafter 
cannot be brought into a thrusting action without cutting so deeply 
into the tye beam as to impair its strength very materially, as 
will be seen in Fig. 217, in which the part k is quite ineffective, 
and must remain so, unless the rafter is let down so far as to leave 
so little wood at m that the strength of the tye would be destroy- 
ed, unless it was very considerably larger than the rafter. It 
therefore becomes necessary to convert the lower end of the rafter 
into a tenon, thus giving up a portion of its pushing surface, in 
order to obtain a sufficient strength of resistance; and several forms 
of tenon have been devised for this purpose, some of the best of 
which are shown at F, G, and H, Fig. 218. At F it will be seen 
that the whole body of the rafter descends but a very small dis- 
tance into the tye beam; the remaining portion of it being cut 
into a tenon that passes about half way into the beam, and that 
the end /, both of the rafter and its tenon, are cut off at right 
angles to the direction of the rafter, or to its axis or line of pres- 
sure. When the abutment / occurs very near the end of the tye 
beam there may be danger of the portion of wood between the 
end of the hole and that of the beam breaking out by giving way 
to the lateral pressure, consequently every precaution should be 
used to carry the bearing points as far as possible into the body of 
the beam, and this is in some measure accomplished by the form 
shown at G, in which there are two bearing shoulders in the depth 
of the rafter, placed one behind the other, in addition to the 
tenon which unites them. H is a form that may be adopted when 
no part of the rafter is let into the beam, but a tenon only is used. 
That tenon, whatever may be the thickness of the rafter, may 
have a thickness equal to one-third of the tye beam, and by having 
two shoulders of different depths, one behind the other, it will 
take a very firm hold. The mortice joints of rafters to tye beams 
are seldom pinned through, because the weight of the rafters and 
the roof they support are amply sufficient to hold them down, and 
pins might interfere with the rafter taking its full bearing on the 
solid wood, 

1001. Struts, braces, and other pieces destined to bear great 
compressive loads, will need no other mortice than that which is 
sufficient to keep them from sliding laterally out of their places, 
in the event of their becoming loose from contraction of materials, 
or the load they have to sustain being relaxed by any cause. The 
more flat and regular the surfaces of such pieces can be made and 



544 OF CARPENTRY. 

the more efficient they will be, therefore struts are very frequently 
well fitted and nailed into their places instead of being morticed; 
or, if a mortice joint is used, it ought to be one with a short and 
thin tenon, merely to retain the parts in their places rather than 
to produce resistance. 

1002. All joints that are subject to great strains should be 
strengthened by iron ties or straps, and particularly the junctions 
of principal rafters and king or queen posts with tye beams; and 
the general form of such iron ties will be seen in all the represen- 
tations of roofs we have given, see Figs. 197, 199, 202-3-4 and 5, 
in all of which y represents the ties of rafters, and x ties of king 
and queen posts. The latter, as commonly used, are very simple, 
being merely a bar of flat iron three or four inches wide, and from 
five-eighths to three-quarters of an inch thick, so bent that it may 
embrace or pass under the tye beam and up the two sides of the 
king or queen post, as shown by Fig. 219, in which w is a side view 
of a king post with a double tenon at its lower end passing through 
the tye beam p, drawn as a transverse section, and both surround- 
ed by the iron strap or stirrup o q q passing from two to three feet 
up each side of the post, and corked or turned outwards at its up- 
per ends q q. These corkings are made for the purpose of resting 
upon square iron staples which are driven into the sides of the 
post. Another pair of similar staples, are usually driven over 
the strap lower down, and its fixing is finished by a few spikes 
driven through holes left in it for the purpose. We thus have a 
strong and expensive strap of iron to assist the strain upon the 
joint, which by its mode of fixing is reduced to the strength of a 
few nails. In using such irons, I have generally had the corkings 
made longer, and turned inwards instead of outwards, so that they 
may pass into holes made to receive them in the timber of the 
king post, the staples and nails being applied as before, and now 
such a strap cannot sink without tearing its corkings out of the 
timber. The best form for a king post strap is, however, that 
which is shown at Fig. 220, in which J is a side view and K a sec- 
tion. J shows the side of the strap or stirrup, which is similar in 
every respect to the one just described, except that it has no cork- 
ings at its upper ends, but in lieu of them the ends are expanded, 
and punched with opposite rectangular holes, for the purpose of 
receiving the gib r, and cross keys or wedges s, shown in the sec- 
tional figure K. A hole corresponding in size and position to those 
in the iron is made through the timber, its bottom being rather 
above the bottoms of the holes in the iron, and into this the gib is 
introduced and dropped, its office being to retain the two plates 
of the stirrup close to the sides of the post, and to form a hard bot- 
tom for the wedges to work upon. The wedges are then introduced 



JOINING TIMBERS. 545 

and driven, by which the tye beam and king post are drawn into 
perfect contact; and should a shrinking or settlement afterwards 
take place, the wedges always afford the means of tightening up 
the joints. 

This same figure at J also shows the form of a king post with its 
shoulders, crown, or head piece, and notch for the ridge piece, and 
t is the form of an iron strap that is usually spiked on to each side 
of the crown for more firmly uniting it with the tops of the prin- 
cipal rafters. 

1003. Another mode of uniting timbers, and especially of 
strengthening mortice joints, is shown by Fig. 221. The mortice 
is made as usual, but the tenon must not extend quite through it. 
When put together, an augur hole is bored through the joint and 
up into the post to be united, as at v, and an iron screw bolt being 
passed up this hole, works into a large iron screwed nut, introduced 
by a side holew. The head of the bolt works through a flat iron 
plate w, which must be larger than the mortice hole, that it may 
take bearing all round on solid wood. 

1004. The mode of fixing iron stirrups to unite the (eei of prin- 
cipal rafters with tye beams, as shown atyin the figures of roofs, and 
on a larger scale by F in Fig. 218, is very often erroneous; because 
such straps are frequently strongly spiked, or otherwise fixed to 
the tye beam at right angles to the rafter; consequently it may 
be presumed that the lower ends of these straps are immoveable. 
But the change that takes place in the position of a rafter by being 
loaded and exposed to the action of time and humidity is a partial 
sinking, and extension or spreading towards the end of the tye 
beam. A stirrup so placed has only the power of keeping the 
rafter down in its place, which it does not require, but cannot 
counteract either of the defects just mentioned; for should the 
rafter sink, it will be disengaged from the iron, and should it ex- 
tend, the iron will bend and follow it, or break off at x. All iron 
tyes should be so placed; that they may be able to resist the 
change they are intended to counteract, in the direction of their 
length; consequently such a tye ought to be placed as nearly as 
possible coincident with the direction of the tye beam, or at any 
rate in a much more sloping form than is generally met with, and 
of course it should be let into a notch on the upper surface of the 
rafter to prevent its sliding upon it. Fig. 222 shows a stirrup so 
fixed, and instead of being nailed to the sides of the tye beam it 
terminates in loops or eyes, through which, and the beam, a strong 
screw bolt is passed, which not only attaches the stirrup more 
strongly to the beam than nails can do, but permits a motion by 
which the tie can adjust itself to any varying strain between the 
beams, without danger of its breaking off. 

69 



546 OF CARPENTRY. 

1005. The principles that have been explained will render 
very few observations on the construction of floors and ceilings 
necessary. A floor is a flat platform of timber, generally formed 
by placing beams across any opening to produce strength, and 
covering them with close-jointed boards, to obtain a flat continu- 
ous surface. Ceilings, on the contrary, are the coverings of the 
tops of rooms, which, in like manner, are formed by fixing beams 
of less strength, upon the under sides of which, laths are nailed to 
receive lime plastering, or they are occasionally covered by thin 
boards. The timber beams thus used to support floors are called 
joists, or sometimes ^007*^015^5, to distinguish them from those used 
for ceilings, which are always called ceiliiig joists. Ceilings are, 
however, very frequently formed upon the under sides of the floor 
joists, when, of course, separate ceiling joists become unnecessary. 

1006. When the span to be floored over does not require joists 
of greater length than from ten to fifteen feet, the joists are simply 
pieces of timber laid from one wall or support to another; and for 
the reasons before given, (807,) such joists are always thinner 
than they are high or deep. Of course it is quite necessary that 
all their upper sides should be perfectly flat and level, that they 
may afford an even bearing for boards to be put upon them; and 
as the width of scanthngs are seldom attended to by sawyers with 
such precision as to render them fit for this purpose, the necessary 
equality of depth and consequent even surface is produced by cut- 
ting away parts of their under surfaces, where they take their 
bearings upon the bond timbers, templates or breast summer, pre- 
pared to receive them; for floor joists ought not to rest on brick- 
work, but on a plate of timber worked into the bricks to receive 
them. When the size of openings is larger than above named, 
the middle of the line of joists will require support, and this is 
obtained by one or more girders or whole timbers passing from 
one side of the building to the other. 

1007. Girders are differently disposed according to the nature 
of the building to be produced; but they should always be die 
square, and their ends should rest on templates of wood, or cast 
iron worked into the side walls. In rooms that are longer in one 
direction than in another, the girders should always extend 
between the two nearest walls, and they ought not to be scarfed, 
but should, if possible, be formed of single pieces of timber. 

1008. Long whole sticks of squared timber will rarely be found 
quite straight, and when curved (probably from want of even 
bearing during its seasoning,) they are said to camber, or to have a 
camber, and timber that is so cambered is generally selected for 
girders; and in using it, the convex side is laid upwards, for all 
new floors that are large and unsupported from below, ought to 



FLOORS. 547 

be so laid that they may be convex upwards to a small extent. 
In this way the floor will probably become level by time and use, 
for as all long timbers, when only supported at their two ends, 
will naturally sink or swag by their own weight, the reduction of 
the camber by this means produces a flat surface; while if the 
floor had been made perfectly flat in the first instance, it would 
very likely become concave in its central part. 

1009. In mills, store-houses, manufactories, and such buildings 
as generally fall under the superintendence of the Engineer, and 
where strength rather than beauty is required, the joists are 
usually mereFy laid across the top of the girder, at right angles to 
its direction, with no other preparation than merely notching 
their under edges down upon the top of the girder to such an 
extent as will produce an even surface for the boarding when 
placed on their tops. Or sometimes the tops of the girders and 
bottoms of the joists are notched or halved into each other, which 
prevents both from shifting out of their places. This construc- 
tion, however, interferes materially with the headway in rooms, 
and causes the building to be higher than it otherwise need be, 
particularly if ceilings have to be made under the floors. Thus 
let a a, Fig. 223, represent the transverse sections of two girders, 
each 14 inches deep, and b the joists laid upon them, suppose 9 
inches deep, with 1^ inch boards nailed upon them, then the dis- 
tance from the bottom of any girder to the top of the floor it sup- 
ports will be 24j inches, and should a ceiling flush with the 
bottoms of the girders be required, then this height will be en- 
tirely lost in each floor. The usual manner of ceiling such a 
floor is, however, to nail the plastering laths immediately on to the 
under sides of the joists, leaving nearly the whole girder visible 
by projecting into the room below. If a flush ceiling is required, 
or one to hide the girders, that is produced by morticing slight 
ceiling joists c in between the girders, and so close to their under 
sides that the laths nailed upon them may pass over the girders 
without producing any projection. It is not, however, deemed 
right in good buildings, to form plastered ceilings immediately 
upon the under side of floor joists, because plastering is brittle 
and liable to crack, and even give way from the concussions and 
vibrations of the floor above; but when separate ceiling joists are 
adopted, the plastering becomes much more detached, and less 
liable to derangement. 

1010. The floor, represented in section by Fig. 223, may be 
considerably diminished in height by notching each of the joists 
about four inches on to the top of the girder, and notching the 
girder down about an inch at each crossing of the joists. This 
will lower the floor five inches without materially affecting 



548 OF CARPENTRY. 

its strength. But the usual method that is adopted in house build- 
ing, and other erections where height of rooms is desirable, is to 
compress the whole thickness of the floor into the depth of the 
girder alone; and this is done in two ways. One is to mortice 
the ends of every joist into the sides of the girders, letting the tops 
of all be flush or even to receive the floor boards, in which case 
the joists are called bridging joists, and the other is to introduce 
strong joists morticed into the girder at about six feet asunder, 
such joists being as deep as the girder itself, and called binding 
joists, and then to notch down the common or bridg;ing joists upon 
them in directions parallel to the girders themselves, separate 
ceiling joists being used in both cases. The floor framed with 
binding and bridging joists, takes rather less timber than that 
with bridging joists alone, for notwithstanding the binding joists 
are deep, yet they are few in number compared with the cross or 
bridging joists, which may be made small in consequence of their 
short bearings. The saving is not material, but it is thought that 
greater strength is obtained out of the same quantity of timber, in 
consequence of the girder being less maimed by mortice holes: 
But it will hereafter appear that if these holes are properly 
placed, they abstract less from the strength of a stick of timber 
than might be supposed. 

1011. Holes are very frequently required to be left through 
floors and roofs for the passage of chimney shafts, wells for stair- 
cases, trap doors, the introduction of sky-lights, &c., and when 
these require to be wider than the distance between one joist or 
rafter and another, a cross piece must be introduced to carry 
their ends, and such piece is called a trimmer. Fig. 224 shows 
the distribution of the parts of a common floor, d d being a brick 
wall with a wall-plate, string of bond timber, or template worked 
into it to receive the ends of e e, w^hich are common joists, butjT 
being a fire place, the joists could not be carried into it without 
danger of being burnt, therefore a trimming or binding joist, 
stronger than the others, is fixed on each side of the chimney, as 
at g g, and A is a trimmer morticed into these two side joists for 
carrying the ends of the intermediate joists, thus keeping them 
out of the reach of any detrimental action of the fire. The space 
h between the front or breast of the chimney and the trimming 
piece is filled up with curved or arched brick- work for supporting 
the hearth. A girder i is introduced to support the rafters at 
about every eight or nine feet, when the length of the room is 
such as to render this precaution necessary. When the rafters 
are so long as to be capable of vibrating laterally, a floor may be 
rendered more stiff* and steady by driving short stretching boards, 
as at k k between every joist; and when it is necessary to cut off 



FLOORS. 549 

the transmission of sound through a floor, it should be pugged. 
That is, inch strips are nailed on to each side of every joist about 
six inches below their upper surface, to support short pieces of 
board to be fitted in between them, and with which the whole 
surface of the openings must be covered. The spaces between 
the joists are then filled in with saw-dust alone, or made up into 
a paste like mortar with wet clay. If the wet composition is 
used, it must be allowed to become dry before the flooring boards 
are nailed down. 

1012. The best wood for flooring boards is yellow pine or oak, 
and in good buildings they ought to be inch and half thick, at 
least, before planed. The boards are only planed (or dressed) on 
their upper surfaces and two edges, and as the perfection of a 
floor is to be perfectly flat and free from inequalities, that is 
brought about by what is called gauging the under sides of the 
boards, an operation that is much easier to make perfect, and 
requires less labour than would be attendant on planing the entire 
under surfaces of the boards. It consists in rebating or cutting 
away, by a plane made for the purpose, about an inch in width 
from the under side of every board at both its sides, as much of 
the wood as will make the finished edges of all the boards of 
exactly the same thickness, as proved by a gauge or measure 
made for the purpose. That done, the projecting intermediate 
quantity of wood on the under side of the board is cut away by 
an adze, so as to unite the two gauged edges in a right line at 
that part that comes over every joist; consequently when boards 
so prepared are laid, and nailed upon the joists, they must form 
an even surface, provided the joists have been correctly laid. 

1013. The best floors are laid with battens, that is, narrow 
boards cut out of the middle of the timber, so as to be of uniform 
colour, and quite free from sap. They are distinguished as bestf 
second best, and common. The best are entirely free from knots, 
shakes and cross-grained fibres; but small knots and irregularities 
are admitted in the second best. They run from four to seven 
inches wide, after which width they loose their name, and are 
boards. The reason for using such narrow pieces as battens in 
the best floors, is, that they are less likely to curl or warp, 
and to shrink than wider boards. Floors are distinguished by 
different appellations depending on the manner in which the 
boards are laid, such as /biding or straight joint Jloors, rebated floors, 
grooved a?id tongiied floors, and dowelled Jloors. The first is the 
most cheap and common method of laying boards. The edges of 
the boards being well jointed by the plane, that is, made as per- 
fectly right lined as possible, the first is laid in its place upon the 
joists, and fastened by driving two flooring brads through it into 



550 OF CARPENTRY. 

every joist. The next board being now put down in its proper 
place, is driven into close contact with the edge of the tirst by a 
screw or lever apparatus made for the purpose, or by the appli- 
cation of wedges, and is nailed down while subject to this pressure. 
The same operation is continued until the whole floor is covered. 
If the boards are not long enough to reach the entire extent of 
the room, the end of one board must abut against the end of the 
other, and such joints are usually broken as in brick-work, that 
is, abutting joints should not be contiguous, but should be carried 
some distance along the side of the next whole board; but all 
abutting joints must come over a joist, so that the ends of both 
boards may be supported. Flooring brads are tapered iron wedges 
without heads, which would disfigure the floor, and when the 
nailing of a floor is finished, these brads are punched or driven 
below the surface that they may be out of the way of the smooth- 
ing plane which is passed over the floor to remove any ridges or 
small inequalities in the joints, and give a last finish. Flooring 
boards ought to be planed, and set by under exposure to the air 
in a dry place long before they are nailed down, because all 
boards will shrink with time in dry places, and this often proves 
inconvenient in straight jointed floors, because when the joints 
open, they permit wind, dust, and the water with which floors 
are washed, to pass through them, to obviate which rebated or 
ploughed and tongued floors are adopted. 

1014. A rebate (pronounced rabbit,) in joinery is a longitudinal 
right angled indentation made in the edge or side of any thing, by 
a tool called a rebating plane. Thus the cavity that is formed 
in window sashes to receive the glass and putty is called a rebate; 
and in like manner if we cut away half the surface of the edges 
of two boards to a certain depth, as at /c / and m, Fig. 225, such 
boards would be said to be rebated on their edges. Half the 
thickness of the board is cut away from the upper surface at A:, 
and half from the under surface at I, consequently if these two 
edges should be applied to each other they would form the over- 
lapping joint shown at m, which is called a rebated joint, and such 
is a rebated floor, in which the boards, being so fitted together, 
are pressed and nailed as before described. 

1015. The groove and tongue joint is still more close and effec- 
tive against the passage of air or water. In this, one edge of each 
board is double rebated, or rebated from each side, so as to leave 
a projecting tongue or fillet, as at n, Fig. 226, in the middle of the 
thickness of the board, equal to about a third of its substance; 
and a corresponding groove or cavity is cut on the other edge of 
each board, as at o; consequently when two edges so prepared 
come together a joint like p is produced. The groove is cut by 



FLOORS. 551 

a tool called a plough plane; hence it is a common expression to 
say a groove is ploughed out of a piece of stuff: and, indeed, the 
joint itself is as frequently called a ploughed and tongued joint, as 
a grooved and tongued one. 

1016. The double groove and slip, or tongue joint, produces the 
same effect as that last described, and is more common, because 
it takes less labour to produce it, and wastes less boarding. In 
this joint both the edges of each plank are grooved or ploughed 
out, and the slip or tongue is a separate strip of wood, so wide as 
to be capable of filling both grooves, when the edges of two boards 
are put together. Neither of those joints are so good for floors as 
the rebate, because in that, half the thickness of the board is left, 
while in the groove and tongue joint, each projection has but one- 
third of its thickness; consequently, this joint is most liable to be 
broken by concussions upon the floor, or by its settling out of its 
level position. 

1017. Dowelled floors, which are alwayfe used in the best finish- 
ed rooms, are put together by a more slow and tedious process. 
The battens are usually straight jointed, and half inch holes being 
made exactly opposite to each other in each of the two edges that 
are to come together, round pins or dowels of wood, fitting the 
holes, are put into them, as before described for fixing stone-work. 
(888.) The first board is nailed down at its outer edge only, so 
that the nails may be hidden by the skirting or wash-board with 
which the best rooms are always surrounded. The other side of 
the board is then nailed, not through the top of the board, but ob- 
liquely through its side, and so of all the other boards in succes- 
sion: for the first board being fixed down, the dowells of the next 
will hold one side of it, and the oblique nails hold the other; con- 
sequently in such floors, not a single nail appears. The dowells 
are always placed, one between each joist, and frequently one 
over each joist in addition. 

1018. The manner of morticing joists into girders is a subject 
that demands particular attention, because, as before observed, 
(940,) if this is judiciously done, it does not abstract sensibly from 
their strength. Referring to what has been before explained (788) 
respecting the effects that take place when a horizontal beam is 
subjected to pressure from above, it will be recollected that the 
fibres in the lower part of such beam are thrown into a state of 
expansive strain, while those in the upper part are put into a 
state of compression. That being the case, if a cut or division 
should be made about half way through the beam from its upper 
edge, the beam would be very materially weakened; because, now 
all that which was resisting matter has been removed, and the two 
sides of the cut would come together. But if after making such a 



552 OF CARPENTRY. 

cut we fill it up again with any hard nnatter, capable of affording 
the same, or a greater resistance to connpression than the wood 
could do before it was renaoved, the strength of the beam will not 
be impaired in the slightest degree. This was fully verified by 
some experiments of Du Hamel. He took six scantlings of willow 
thirty-six inches long and one inch and a half square, and having 
supported them by props under their two ends, he applied weights 
to the middles of the pieces to bend and break them, and found 
that they all broke with an average force of 525 lbs. Six similar 
bars were then cut one-third through from the top, and the cuts 
being filled up with wedges of hard wood struck in with a little 
force, they were submitted to pressure, and broke with an average 
force of 551 lbs. 

Other six similar bars were cut half through, and being treated 
in the same manner, broke with 542 lbs. 

Six other bars were cut three-quarters through, and broke with 
530 lbs. being a very oiose approximation to the strength of the 
bars before any cut was made in them. 

A similar bar, cut three-quarters through, was loaded until it 
nearly broke, when it was unloaded and the wedge taken out. A 
thicker wedge was now substituted and driven in, so as to make 
the bar straight again by filling up the space occasioned by the 
compression of the wood, and the bar being now loaded, broke 
with 577 lbs. 

From these experiments it is clear that more than two-thirds 
of the thickness of a beam (perhaps nearly three-quarters) con- 
tributes nothing to its strength when subject to the strain and cir- 
cumstances just described. 

1019. We learn further, that as the actions of a beam, subject- 
ed to lateral pressure, are opposite, one part being compressive 
while the other is dilative, that little or no action takes place at 
the axis of fracture, or line where these two forces meet and be- 
come neutral by changing into each other; consequently we may 
take away the solid substance to a certain distance around the 
axis of fracture by boring a hole or otherwise, without sensibly 
impairing the strength of the beam. 

These principles, therefore, point out very clearly how joists 
should be morticed into girders, because if a mortice joint is well 
made the tenon ought to fit the mortice hole very closely and cor- 
rectly. If the mortice hole is made near the top of a girder, it 
will weaken it, because a portion of the solid wood, necessary to 
resist compression, has been taken away; but if the tenon that is 
put into that hole fills it tightly, that will at once supply the de- 
ficiency, because now the tenon becomes the wedge referred to 



FLOORS. 553 

in Du Hamers experiments, and will restore the strength of the 
piece. 

Again, if instead of making the mortice hole near the top of the 
beam, we make it in or near the axis of fracture, or rather below 
the middle of its depth, we may carry the hole quite through, and 
yet not impair the strength of the beam; but in this case the tenon 
must be confined to small dimensions, and would be liable to break 
off close to its shoulder. 

1020. The form of tenon which experience has dictated, and 
which is constantly used by all good carpenters for uniting joists 
to girders, is in perfect accordance with all the principles above 
stated, and gives the greatest possible strength to the joist, with- 
out impairing that of the girder. It is technically called housing 
in a mortice, and its form is shown by Fig. 227, in which A is the 
end of a joist, and B a transverse section of the girder to which it 
is to be joined, showing also a section of the mortice holes cut into 
its opposite sides. The tenon has no side shoulders, but is made 
the full thickness of the joist. Its long tongue r is generally square, 
and should be placed as nearly as may be, opposite the axis of 
fracture of the girder B. If it was of the same size throughout, 
as indicated by the dotted lines, it would be very deficient in 
strength, but by giving its upper shoulder an angular form s r, it 
is not only strengthened, but the load the joist may have to sustain 
becomes supported by above half the depth of wood, and this 
quantity is increased to about three-quarters by the angular pro- 
jection left in the under shoulder at t, so that the only ineffective 
part of the joist is between t and v; and when the girder is deeper 
than the joist, that becomes nothing, because the tongue r will be 
lowered. The mortice holes in the sides of the girder are cut into 
exact correspondence with the form of the tenon, and this will 
maim the beam in the smallest degree, because no solid wood is 
taken from its under, and very little from its upper part, owing to 
the sloping direction of the housing; and the main strength of a 
beam we have seen, is posited in its extreme sides. The chief 
cutting away occurs at, and near the axis of fracture, and there 
less solid wood is necessary than in any other place. 

1021. As timber is limited by nature in the extent of its growth, 
it frequently happens that sticks of sufficient strength and stiffness 
cannot be obtained for the construction of large works, especially 
for the girders of floors, which, from their nature, will not admit of the 
means of support already described, as applicable to the tye beams 
of roofs; and when this is the case such extraordinary large beams 
must be huilt up, or the largest beam that can be obtained must 
be trussed. Building a beam is joining a number of beams together 
by the processes already explained under the names of scarfing 

70 



554 OF CARPENTRY. 

(992), and joggling (855), and is extensively used in the construc- 
tion of the masts of large ships, and in the stupendous timber 
bridges erected in different parts of the United States, and which 
in point of skill and boldness of conception and execution, are equal 
to any thing of the kind in the world. 

1022. Trussing a beam is the introduction of certain stiff, com- 
pact, and strong materials into the inside of it, for the purpose of 
increasing its strength and stiffness, and as these materials are dis- 
posed in forms accordant with those already described for giving 
support to the trusses of roofs, the process is called trussing. To 
construct a trussed beam, two large sticks of timber must be pro- 
cured exactly the same in dimensions; or one large stick may be 
sawed longitudinally through its middle so as to convert it into two 
equal pieces, according to the size and strength required in the 
beam to be produced, and the deeper these pieces can be got 
from top to bottom the better they will be for the intended pur- 
pose. The simple truss is produced by letting scantlings of oak or 
other hard and compact timber into these pieces, in the form and 
manner shown at L, in Fig. 228, which represents one of the 
above mentioned pieces, and a a are two scantlings of oak four 
inches square, let into the piece by carving or chiselling out two 
channels or cavities, corresponding with the size of the oak pieces, 
and placed in the angular direction shown in the figure. These 
channels are only half as deep as the oak is thick, therefore the 
oak pieces, when introduced, project half their thickness out of 
the first piece of timber, and a similar pair of channels is cut in 
the second piece, so that when the two halves are laid together 
they can meet and touch, and the oak pieces will be completely 
hidden between them. An iron abutment bolt, having shoulders 
at right angles to the directions of the oak pieces, and a head that 
spreads over them, is also let into the middle of the pieces, as at 6, 
and the oak pieces abut against it, while their lower ends come into 
contact with flat and acute wedges of iron or hard wood c c. The 
two halves of the beam being put together, with the several pieces 
just named between them, are held in permanent contact by a 
number of iron screw bolts and nuts passed through holes indicated 
by black dots in the figure, so that the beam, when finished, looks 
like the figure marked M if viewed from one side, and like N in 
plan, or when viewed from above. The scantlings of oak are 
sunk into grooves that fit them, to prevent the possibiHty of their 
becoming shorter by bending; and by tightening the nut of the 
bolt 6, and driving the wedges c c, it can be brought to any re- 
quired degree of compression, and an effectual truss will thus be 
produced; for the bottom of the beam, between c c, will act the 
part of a tye beam, the bolt 6 of a king post, and a a two opposite 



TRUSSING BEAMS. 555 

principal rafters, and as the centre of a beam so trussed cannot 
descend, without compressing and shortening the pieces of oak, so 
of course such a beam must be much more stiff than another 
without such preparation. Accordingly trussed girders and breast 
summers are frequently used. 

The principal points to attend to in trussing a beam, are the 
selection of a material for the truss that will afford ample resist- 
ance to compression, to give the pieces good and immoveable 
abutments, and make the angle of the truss as little obtuse as 
possible. Hard and well seasoned oak is, on this account, gene- 
rally used for the trussing pieces, but cast iron is often resorted to, 
and to diminish its weight, the form shown by Fig. 158 is adopted, 
but is terminated by flat plates or flanches at the ends, to increase 
the abutting surfaces. Iron trusses of this form require a very 
small portion of the beams to be cut away, because it is not ne- 
cessary that the two inner faces or cheeks of the beam should come 
into contact. When the trusses are of wood, the central abut- 
ment is frequently made of hard wood also, when it should have 
the dovetailed form, shown at O, to prevent its rising upwards in 
the beam. But the iron screw bolt before mentioned is better, 
because it admits of tightening up the truss in any degree after it 
is put together, or in case of the beam sinking by the effect of 
time. The wedges c c are likewise often made of wood, but are 
better of wrought iron, because thin wood is very liable to split 
and crush under a heavy strain. The wedges should be made 
as broad as possible so as to distribute the pressure over a large 
surface of the section of the beam, but their width ought not to 
exceed one-third of the width of the beam. The wedges should 
also be placed at considerable distances from the extreme ends of 
the beam to prevent the timber that supports them being split and 
forced out of its place, for if the end abutments, or either of them 
give way, the power of the truss is gone. These wedges should, 
therefore, never be on the walls, or in places where the timber is 
liable to decay; but they may be put two or three feet within the 
walls, as timbers seldom break near their supported ends, and re- 
quire assistance about their centres. This circumstance likewise 
assists in permitting us to make the angle of the braces less obtuse; 
since the nearer the abutting points c c are together, and the 
greater the depth of the beam in the centre, and the greater will 
be the power of the truss. 

1023. Another method of improving the position of the angle, 
and thereby obtaining a longer trussed beam than can be made 
by the introduction of the simple truss just described, is to use a 
compound truss consisting of two braces as before, with a straining 
beam between them, as shown by Fig. 229. All that has been 



556 OF CARPENTRY. 

said on the construction of the former trussed beam applies equal- 
ly to this: the only difference in their form being, that instead of 
the two braces meeting and abutting against a single bolt or key, 
they abut, in this construction, against two such bolts or keys, 
which are kept asunder by the interposition of the straining piece 
d d. This piece will have a constant tendency to spring upwards, 
or rise out of its place, but is restrained from doing so at its two 
ends by the heads of the abutment bolts at d d. The piece may, 
moreover, be made wider than the braces, so that it may be 
housed throughout its whole length on both sides in the two cheeks 
of the beam, or it may be held down by T headed or staple bolts 
passing through the beam, and fixed by screw nuts on its under 
side. 

Notwithstanding a beam is strengthened and stiffened by truss- 
ing, still this process does not give so much additional strength as 
it is generally supposed by workmen to do, on account of the great 
obliquity of the braces of the truss, unless the beam is short, or the 
point of the truss is carried above it, which is frequently done 
when the height of the building permits a considerable loss of room 
beneath the floors. Thus Fig. 230 shows a timber girder so 
framed, in which all the parts will be obvious after the description 
already given. In using a girder of this kind, the joists cannot 
evidently be morticed into it, but a series of binding joists a aa a 
are blocked up upon the top of the girder by pieces of timber b 6, 
and then common bridging joists are fixed upon them, as at c c, 
having their upper surfaces even or level with the highest part 
of the truss, so that the flooring boards can be laid without any 
interruption, 

1024. Trussed girders are frequently made of cast iron instead 
of timber, especially in mills and manufactories; but if the span 
is large, cast iron alone should not be trusted. This metal will 
bear an immense strain of compression, but being brittle, it is less 
trustworthy against extension, especially if subject to jars or con- 
cussions, therefore the tye beam, or part exposed to an extending 
force, should be of bar or malleable iron. Fig. 231 is a principal 
beam or bearer so constructed. The cast iron is disposed in three 
plates or pieces, with flanches to them, so that they can be put 
together with iron screw bolts and nuts, by straight joints at d d. 
The end pieces may both be cast from one pattern, and large 
perforations are left through all the plates to produce lightness. 
A wrought iron tye bolt e, having a head at one end and a screw 
and strong nut at the other, (or a hole through the bolt and a 
strong iron wedge or key,) by which the bolt is drawn straight 
and tight, will effectually prevent the truss from sagging or 
dropping in its middle. This bolt should pass through long sockets 



TRUSSING BEAMS. 557 

cast near the feet of the truss, and it is better to hang the bolt up 
by eye-bolts or staples, to the under side of the cast iron, not only 
to prevent its sagging, but likewise to check its vibrations. The 
casting, although spoken of as being made in three pieces, will be 
better made in two, or even in a single piece, provided the open- 
ing is not too large. Such an iron truss is only used to give sup- 
port and assistance to a floor of wood, iron, or any other material; 
therefore small girders or binding joists will have to be placed 
transversely over it, as atyy, and common joists are then put over 
them in the same way as if no iron truss had been introduced. 

1025. In the construction of a common king post roof, all the 
pieces, except the king post, are kept in a state of compression, 
and that in extension; but the principles will not be affected if 
extension is substituted for compression, provided proper materials 
are selected to withstand the force; and accordingly this mode of 
construction is very commonly adopted for the beams of steam 
engines, thus producing a lighter and more economical beam than 
could be obtained in any other way. Fig. 232 exhibits the form 
of such an engine beam, in which the parts g g^hh, are of cast 
iron, by no means strong enough to answer the intended purpose, 
but by fixing and straining the four wrought iron bolts iiii by 
means of screw nuts formed upon their ends for the purpose, a 
vast increase of strength and stiffness will be produced; for now no 
part of the cast iron beam gg can bend without straining or break- 
ing some of the rods iiii. The cast iron projections hhhh add 
nothing immediately to the strength of the beam, but perform an 
important office in maintaining the right lined direction of the 
wrought iron rods, and preventing their vibration. 

1026. It seldom happens that timbers cannot be procured of 
sufficient length to reach across an opening to be floored over, but 
as this case may occur. Fig. 233 shows a means by which short 
timbers may be employed. One end of each piece works into a 
wall and the other ends are halved, or fitted upon each other in a 
manner that will be sufficiently obvious on inspecting the figure. 
By an extension of the same principle a large naked floor may be 
constructed. 

1027. The dimensions of timbers to be introduced into roofs may 
be very accurately ascertained, because the weight of the roof 
itself, and of the materials with which it is to be covered, are 
ascertainable quantities, and may, therefore,be considered as given; 
and, in general, nothing requires to be added to the amount of 
this load, except a provision for the weight of snow that may fall 
and lodge upon a roof, which ought to be provided for, and this 
will more than amply cover the weight of a few men who may be 
engaged in occasional repairs. But if a roof is in any place that 



558 OF CARPENTRY. 

is likely to be crowded with spectators of any public exhibition, 
allowance must be made for such occurrence. Indeed, all roofs 
ought to be made considerably stronger than is necessary for the 
support of their own materials. With floors the case is very dif- 
ferent. In general they cannot have the support that is given to 
roofs, and yet they are subject to much more mutable loads, be- 
cause a room may sometimes be empty, and at other times may 
be crowded with persons, or may be converted into a warehouse 
or depository for heavy goods. Of course, therefore, floors require 
to be made much stronger in proportion than roofs, and the follow- 
ing rules for proportioning timbers, extracted from Tredgold's 
Elementary Principles of Carpentry, may be found useful. In the 
following rules for roofs, the pitch, or height of the roof, is con- 
sidered as one-third of the base or span. 

1028. Tye Beams. — To find the scantling of a tye beam that 
has only to support a ceiling; the length of the longest unsupport- 
ed part being given. 

Rule. — Divide the length of the longest unsupported part, by 
the cube root of the breadth; and the quotient multiplied by 1.47 
for fir, or by 1.52 for oak,* will be the depth required, in inches. 

Example. — Let the longest unsupported part be 17 feet, and 
the thickness of the beam be 9 inches. Then the cube root of 9 

17X1 47 
is 2.08 very nearly; therefore '- — =12 inches, the depth re- 
quired. 

If the tye beam has to support rooms formed in the roof, then 
the rule for its depth will be the same as for girders, which see. 

King Posts. — Rule. Multiply the length of the king post in ieet 
by the span of the roof in feet. Then multiply this product by 
the decimal 0.12 for fir, or by 0.13 for oak, which will give the area 
of the king post in inches: and dividing this area by the breadth 
will give the thickness; or by the thickness will give the breadth. 
The scantling thus obtained applies to the shaft, or small part of 
the post, exclusive of the spreading haunches or shoulders. 

QuEEN^ Posts. — The rule is the same in principle as for king 
posts, but is worked differently, because the king has the whole 
tye beam to support, and the queen only a part of it; therefore 
multiply the length of the queen post by the proportional part of 
the length of the tye beam that the post has to support; and this 
product multiplied by 0.27 for fir, or 0.32 for oak, will give the 

* The constant numbers used as multipliers in this and the following rules have 
been taken from a comparison of many roofs and other constructions already- 
executed, and known to stand. 



ESTIMATING THE SIZE OF TIMBERS. 559 

area of the post in inches. Its thickness or breadth will be found 
as above. 

Principal Rafters presumed to be strutted or supported under 
each purlin. 

Case 1st. To find the medium or average scantling when there 
is a king post in the middle. 

Rule. — Multiply the square of the length of the rafter in feet, 
by the span of the roof in feet; and divide the product by the cube 
of the thickness in inches. For fir mirltiply the quotient by 0.96, 
which will give the depth in inches. 

Case 2nd. To find the average scantling when there are two 
queen posts. 

Rule. — Multiply the square of the length of the rafter in feet 
by the span in feet, and divide the product by the cube of the 
thickness in inches. For fir multiply the quotient by 0.155, which 
will give the depth in inches. 

The thickness of principal rafters is generally the same as that 
of the king post; consequently depth only has to be determined, 
and average scantling is here mentioned, because principal rafters 
generally taper or diminish (976), the depth at the top being 
about an inch less, and at the bottom an inch more than that at 
the centre. 

Straining Beams. — In order that this beam may be the strongest 
possible, its depth should be to its thickness as 10 is to 7. 

Rule. — Multiply the square root of the span in {eet by the 
length of the straining beam in iee-t, and extract the square root 
of the product. Multiply the root by 0.9 for fir, which will give 
the depth in inches. To find the thickness, multiply the depth by 
0.7. 

Struts and Braces should be placed as nearly perpendicular as 
possible to the action of the strains they have to withstand. 

Rule. — Multiply the square root of the length supported in feet 
by the length of the brace, or strut, in ieeU and the square root 
of the product multiplied by 0.8 for fir, will give the depth in 
inches; and the depth multiplied by 0.6 will give the breadth in 
inches. 

Purlins. — No part of a roof is more likely to give way than 
the purlins. They seldom break, but they sag or sink between 
one principal truss and another, thus destroying the uniform flat 
surface the face of a roof ought to preserve. To obviate this 
they ought not to be pinched in scantling, nor should they be mor- 
ticed into the principal rafters, as sometimes done, but should lie 
over them, as already described (977). They ought likewise to 
be put on in as long lengths as can be conveniently obtained. 

Rule. — Multiply the cube of the length of the purlin in {eeU by 



560 OF CARPENTRY. 

the distance the purlins are apart in feet; and the fourth root of 
the product for tirwill give the depth in inches. Or multiplied by 
0.04 will give the depth for oak; and the depth multiplied by 0.6, 
will give the breadth. 

Common Rafters are seldom or ever calculated, because com- 
mon quartering or scantling of 4 by 2^ inches, is amply strong 
enough for all purposes. But for small roofs to be boarded and 
shingled, or covered with light materials, a smaller size may be 
used with safety. 

Common rafters and purlins should be made of straight grained 
pine or fir, in preference to oak, elm, or other woods; because it 
is less liable to warp and twist with the sun's heat than most 
other kinds of timber. 

1029. To Estimate the size of Timbers for Floors. 

Common or Bridging Joists. — As the strength of joists depends 
much more on their depth than their breadth, all joists should be 
thin and deep. Indeed, there is no advantage in thickness beyond 
what will give sufficient stiffness to avoid lateral vibration, and 
afford a sufficient surface for nailing the boards to. Common joists 
need therefore never exceed three inches in thickness, nor should 
they be made less than two inches. The thickness having been 
determined, the depth alone has to be sought by the following 

Rule. — Divide the square of the length in feet by the breadth 
or thickness in inches, and the cube root of the quotient multi- 
plied by 2.2 for fir, or 2.3 for oak, will give the depth in inches. 

Binding Joists and Trimmers. — These admit of two cases. 

Case 1st. To find the depth, when the length and breadth are 
given. 

Rule. — Divide the square of the length in feet by the breadth 
in inches, and the cube root of the quotient multiplied by 3.42 
for fir, or 3.53 for oak, will give the depth in inches. 

Case 2nd. To find the breadth, when the depth and length are 
given. 

Rule. — Divide the square of the length in feet by the cube of 
the depth in inches, and multiply the quotient by 40 for fir, or by 
44 for oak, which will give the breadth in inches. 

These rules suppose that the distance between the binding joists 
is six feet: if the distance apart be greater or less, the breadth, 
given b}^ the rule, must be increased or diminished in proportion; 
but binding joists should never be more than six feet apart. 

Girders. — As the dimensions of girders are frequently con- 
trolled by the dimensions of the timber that can be procured for 
them, two cases may occur, viz; — 



ESTIMATING THE SIZE OF TIMBERS. 561 

Case 1st. To find the depth of a girder, when its breadth and 
the extent of span, or opening to be covered, are given. 

Rule. — Divide the square of the length in feet, by the breadth 
in inches; and the cube root of the quotient multiplied by 4.2 for 
fir, or by 4.34 for oak, will give the depth required in inches. 

Case 2nd. To find the breadth, when the length of bearing and 
depth are given. 

Rule. — Divide the square of the length in feet by the cube of 
the depth in inches, and the quotient multiplied by 74 for fir, or 
by 82 for oak, will give the breadth in inches. 

In these rules, the girders are supposed to be ten feet apart, 
and this distance should never be exceeded; but should the dis- 
tance apart be less or more than ten ^eet, the breadth of the girder 
should be made in proportion to the difference of distance. 

1030. Ceiling Joists require to be no thicker than is necessary 
to nail the laths to, and two inches will be quite sufficient for that 
purpose. 

To find the depth of a ceiling joist, when the length of bearing 
and breadth are given. 

Rule. — Divide the length in feet, by the cube root of the breadth 
in inches, and multiply the quotient by 0.64 for fir, or 0.67 for 
oak, which will give the depth required. 

If two inches be fixed upon for the breadth, (and that is the 
common size,) the rule for ceiling joists of fir becomes very easy; 
for then half the length in feet is the depth in inches. The dis- 
tance apart of these joists is generally from ten to twelve inches 
in the clear; but this must be regulated by the length of laths 
that can be procured, so that they may nail on without waste, or 
the trouble of cutting them. Laths are usually four ieet long, and 
are sold in bundles containing one hundred each. One bundle, 
with five hundred lathing nails, will cover five yards superficial of 
ceiling. 

Ceiling joists should be in long pieces, notched and nailed on to 
the bottoms of the binding joists. A ceiling so put up is less liable 
to crack than when the joists are shorter and morticed into the 
sides of the binding joists, which are not only weakened by the 
operation, but much more time is necessary for its performance. 
They should be made of pine, fir, or such wood as will not warp 
and twist. 

So far, we have only considered such framings as can be 
strengthened and stiffened from above as in roofs; or such as depend 
wholly upon their own strength, as in floors and partitions between 
rooms, or in the sides of framed buildings: but there are many 
cases in which entire or partial support can be derived from be- 
71 



562 OF CARPENTRY. 

low, and these lead to another important branch of carpentry, 
which is 

The CoNSTRUCTioisr of Wooden Bridges. 

1031. There are many places in which bridges may be desira- 
ble, but at which stone cannot be procured; and others in which 
stone bridges would be found too expensive; and as those of timber 
may answer every purpose, and the construction of wooden bridges 
is intimately connected with the two subjects last under discussion, 
a few observations upon them may, with propriety, be introduced 
in this place. 

Wooden bridges have their advantages and disadvantages; they 
are much less costly than those of stone, brick, or iron; for the 
mere centring necessary to build these, will, in most cases, cost 
as much as the expense of constructing an entire bridge of timber; 
and they are, moreover, much more speedily executed. On the 
other hand they are much less durable, owing to the natural 
decay of materials; and when once they do begin to fail, they 
become very troublesome and expensive, and require constant 
attention; because the parts that give way first are generally those 
least seen, as being less exposed to air and light, and they are fre- 
quently the most troublesome to get access to for repairs. Fre- 
quent interruption of the public passage likewise occurs, since it 
often happens that the bridge has to be shut up during the pro- 
gress of its repairs. 

1032. In newly settled countries, timber bridges are generally 
used, because such countries frequently abound in timber, which 
is of comparatively little value; and cheapness and expedition of 
construction are both objects of importance. But as such countries 
advance in population and riches, the timber bridges, when they 
decay, are seldom replaced with the same material, but those of 
greater duration are resorted to. The one construction may be 
said to be for present use, while the other is building for posterity. 
Of this, two bridges of London offer a good example. London 
Bridge, so called, because for many centuries it was the only 
bridge across the River Thames, in that city, was first built of 
timber about the year 994, and 169 years afterwards it was in 
such a state of dilapidation as to be unfit for use; and it was 
therefore rebuilt of timber in 1163; but a portion of it having 
been washed away, it was determined to adopt a bridge of stone, 
which was began in 1176, in the reign of Henry Ilnd., but was 
not finished until 1209, under King John, so that it was thirty- 
three years building; and in 1830 it was taken down, after having 
sustained the immense traffic of London for upwards of 620 years, 



TIMBER BRIDGES. 563 

notwithstanding it was built on the worst principles^ and with lit- 
tle or no attention to science. This bridge had the most severe 
test, for it was one of the greatest thoroughfares in London, and 
was constantly covered with loaded carriages, and passengers of 
all descriptions; the river, where it was built, was 900 feet wide, 
and subject to a tide rise of about 8 feet, but owing to improper 
construction, the water way was contracted to 194 feet, by the 
introduction of 18 enormous stone piers, which supported 20 small' 
arches, so that twice in every 24 hours, or whenever the tide- 
water retired, a most tremendous torrent was rushing through the 
arches, and such a one as must have carried away any bridge 
unless constructed of the most refractory materials. It therefore 
produced a formidable impediment to the navigation of the river, 
and was on this account removed and replaced by a magnificent 
stone bridge of only five arches, which, of course, offered very 
little opposition to the passage of the water or its navigation, and 
on the completion of this new bridge the old one was taken down 
by contract, and the workmen employed declared, that it was so 
well put together, and was formed of such good materials, that it 
might have stood for centuries to come, had not its foundation 
been greatly injured by the violent cataracts of water that flowed 
through its arches and washed the soil away, and laid bare the 
piles upon which the piers were built. These excavations re- 
quired to be constantly filled up with block chalk, as they occurred, 
and this operation was not only a great source of annual expense, 
but tended to the further injury of the navigation. These circum- 
stances are mentioned here merely to show the advantage and 
durability of a substantial stone bridge, and to put them into com- 
parison with another bridge across the same river, only a few 
miles to the west of it, called Battersea Bridge, which was erected 
entirely of timber, about 100 years ago. This bridge, which is 
a great thoroughfare, is a private joint stock concern, supported 
by tolls upon all trafiic and passengers that go over it; and such 
were the constant expenses of its repairs, that the tolls were 
scarcely sufficient to meet them; a constant succession of new 
timber and labour being necessary. It is estimated that within 
the period of 15 or 20 years every piece of timber is renewed, so 
that it may be said the whole bridge is rebuilt every 20 years. 
Of late, parts of the timber have been replaced by cast iron, and 
this may have the eflfect of rendering it more durable. In Eng- 
land no bridge is ever covered over by a roof or side walls to 
afford protection against weather, which salutary precaution is 
adopted in the United States, Germany, and many other countries, 
and no doubt assists in giving a greater duration to timber bridges 
than they could otherwise possess. 



564 OP CARPENTRY. 

1033. The principles of carpentry and framing, as already laid 
down, apply so completely to the construction of bridges of timber, 
that little more can be said on this subject, further than to show 
the several varieties of construction that have, from time to time, 
been adopted, and to point out their respective advantages and 
.disadvantages, as well as the local circumstances that are most 
essential to each of them. 

1034. Timber bridges maybe divided into several distinct forms 
or modes of construction, and we will consider them accordingly, 
from their most simple to their more complicated constructions. 

The simplest and most obvious bridge, which requires neither 
skill in framing, or application of any mechanical principle beyond 
that of mere strength, is formed by laying two, or any greater num- 
ber of trees or pieces of squared timber across the stream, from 
one side to the other, placing them nearly parallel to each other, 
and at right angles to the stream, and fixing other smaller pieces 
upon their tops, pointing in the direction of the river, putting them 
either close together, so that they may be covered with earth to 
form a roadway, or else placing them at greater distances, so as 
to serve as joists upon which planking may be fixed, either to be 
used in its naked state as a road, or to be covered with earth or 
gravel, in which latter case side boards will be necessary to keep 
the materials of a uniform thickness, and prevent their falling 
over the edges into the water below. Such a bridge may have 
rails placed at its two sides, for the protection of passengers, and 
will answer every purpose for short distances, provided the girders 
or main bearing timbers have sufficient strength; and that strength 
may be augmented by placing these timbers nearer together, or 
even in contact, or by using two layers of such timbers one upon 
the other. 

Still in this construction we are limited to dimensions; because 
it seldom happens that timber of uniform size can be obtained of 
more than fifty or sixty feet in length, and if they were to be used 
in such lengths, they would sag or bend downwards in the middle, 
and would have so much elasticity, when a load came upon them, 
that they would vibrate up and down, and thus exclude the pos- 
sibility of forming an earth or stone road above them. The sim- 
plest way of obviating this inconvenience is to drive a row of per- 
pendicular piles into the bed of the river, making the length of the 
row in the direction of the stream, and placing one pile under each 
bearer; or else using fewer piles and surmounting them with a 
cap or sill of timber, upon which the middles of all the bearing 
timbers could rest, and in that way perfect steadiness and stability 
may be given to the bridge, because if a single row of such piles, 
placed in the centre of the pressure, may not be sufficient, other 



TIMBER BRIDGES. 565 

similar rows may be placed parallel to each other, at as small 
intervals as may be necessary to insure perfect stability. 

It may appear that such a bridge is only applicable to very 
narrow rivers or valleys, because we are limited by the usual 
length of timber which ought to be used in single or entire pieces; 
but this is by no means the case, because the same rows of piling 
that have been spoken of as applied to support the middle parts 
of the main bearers, may likewise be used to support the ends; or 
the bearers may break joint, instead of all terminating upon the 
same row of piles; so that the same sill or row of piles that sup- 
ports the ends of the three pieces of timber may support the mid- 
dles of another set of three bearers, and an intermediate part of a 
third set, and in this manner the bridge may be continued over a 
river of any width. 

1035. Devoid of skill, beauty or science, as this mode of con- 
struction unquestionably is, it is, nevertheless, almost the only one 
that is resorted to for the construction of timber bridges in Eng- 
land. Battersea bridge, above referred to, is of this kind, although 
upwards of 300 yards long, and over the finest river in the coun- 
try. The only difference being, that in the largje wooden bridges 
of England, instead of using single rows of perpendicular piles to 
support the bearers or girders, a kind of pier is formed by driving 
several parallel rows of piles very close together, and cross bra- 
cing and tying them together with oak planks about four inches 
thick, placed diagonally so as to act the part of struts and braces, 
thus producing strength and stiffness, preventing the piles from 
getting out of their perpendicular positions, and enabling them to 
resist the impulse of the current running against them, as well as 
the shocks of floating ice, and heavy laden craft or vessels which 
occasionally run foul of them. All these braces or tyes, and 
indeed all parts of wooden bridges, must be put together with 
screw bolts and nuts, wedges, or other contrivances such as will 
permit of the parts being taken asunder; because they will decay in 
time, and it will be necessary to take out and replace parts with- 
out disturbing or maiming those that remain; and this could not 
be effected if the work was firmly nailed or spiked together. 

1036. It may not be possible to introduce rows of piles into a 
river for affording support to a bridge without impeding its navi- 
gation, particularly if it is narrow, and whenever this is the case 
we have no alternative left but to resort to the rules of carpentry 
for obtaining artificial support, and this can be done in several 
ways. Thus, for example, let a b, Fig. 234, be a section of a 
stream to be crossed. We must, in the first place, build founda- 
tions either of stone, brick, or timber, on the opposite sides of the 
water, as at c c, for supporting or carrying the bridge, and these, 



566 OP CARPENTRY 

called abutments in bridge building, ought never to be of timber, 
on account of its liability to rapid decay when in contact with 
the earth, particularly near water, d efis a side view of one of 
the beams of the bridge supposed to be so long as to be incapable 
of bearing a load upon it without swagging or vibration, but by 
applying two angular struts e c, from the middle of the beams, 
and letting their lower ends rest upon offsets or shoulders made 
to receive them at c c in the abutments, the main bridge beams 
will be effectually supported. Should the struts e c be so long as 
to endanger their bending, they may be stiffened by tye or bridle 
pieces introduced, as dotted in at^^. When the opening to be 
crossed is very wide, the angles dec nndfe c will become very 
acute, and thus diminish or destroy the efficacy of the struts, 
unless their abutments can be obtained in very low positions, or 
the platform of the bridge is raised so high as to render it inconve- 
nient of access; for one point to be attended to in the formation of 
all bridges is avoiding any sudden or abrupt rise or fall upon the 
bridge, which ought to assimilate, as nearly as possible, with the 
road of which it forms a part. The struts may be considerably 
shortened by adopting the form shown by Fig. 235, in which the 
length of the bridge is divided into three instead of two parts, and 
a straining beam is introduced between the struts for their upper 
ends to abut against, and this principle is still further carried out 
in Fig. 236, in which two pair of struts, with separate straining 
beams, are used. In both these designs the principal bearing 
beams may be in two or even three lengths scarfed together, 
because they should be bolted through to fasten them to the 
straining beams, and this will materially assist the joint, which 
must be made over such beam. 

1037. The common roof framing is applicable to the formation 
of bridges, because the two side or exterior bearing beams may 
be, framed with king posts and struts, as in Fig. 237, and if trans- 
verse joists are laid over the top of the tye beams they will sus- 
tain the floor or platform of the bridge, while the framing will 
form side parapets or fences, particularly if filled in with rails or 
paling, as shown in one half of the figure. And when a river is 
not navigable, or subject to floods, the principle of the roof truss 
may even be inverted by turning the struts into tyes, and placing 
the king post beneath instead of above the tye beam, as in the figure 
where /i is the inverted king post, audit insteadof being struts, are 
chains or bars of iron drawn tight bj screw nuts upon their ends. 
Such a device will evidently bear up the king post and support 
the middle of the tye beam, but is not so good or trust- worthy as 
the king post truss in its ordinary form, and is therefore never 
used. The principle of roof trussing should, however, be con- 



TIMBER BRIDGES. 567 

stantly resorted to in making the side guard fences or parapets of 
all timber bridges, and is in common use for this purpose in the 
form exhibited by Fig. 238, in which it will be seen that a strain- 
ing beam is introduced between two short queen posts, in order 
to avoid the unsightly height of a king post. A long bridge may 
be constructed by a series of these trusses joined end to end, even 
without connection, provided each junction is supported by a pier 
of timber, bricks or masonry, and the spaces between one strain- 
ing beam and another may be filled up by pieces that appear as 
continuations of them, so as to produce a continued top rail to the 
side fences, as shown in the figure. It need hardly be stated that 
this construction of bridge in which the support is wholly from 
above, may be united with that shown by figures 234, 235 and 
236, where it is from below, whenever the bridge is sufficiently 
elevated above the stream to place the under struts out of the 
reach of floating ice, and then a much stronger construction will 
be obtained of the form shown at P in Fig. 238. 

1038. Another expedient that is frequently resorted to for pro- 
ducing additional strength in truss-framed timber bridges, is to 
divide the road longitudinally into two carriage ways, with a foot 
road between them, or into four parts, consisting of two carriage 
roads in the middle, and two foot paths, one on each exterior side. 
The partitions used to produce these divisions are framed trusses 
exactly like those on the exterior sides, so that by this last mode 
of division five parallel sets of trusses can be carried up above the 
platform or road of the bridge without producing any obstruction 
to its passage, instead of the two exterior ones as first described, 
and in this way the strength and stiflfness of the bridge is very 
much increased. 

1039. It is the custom in the United States, as well as in some 
parts of Germany and France, to cover timber bridges by roofs 
and side walls, which greatly preserves the timber by protecting 
it from weather. But this covering answers another important 
end; that of permitting trusses which rise high above the road- 
way, to be used without producing an unsightly appearance. 
They become necessary for the support of the roof, and at the 
same time afford the means of hanging the roadway up to them, 
in addition to the other means of supporting it, as already described. 
Thus a bridge, such as is shown at Fig. 238, may have a set of 
additional king post trusses placed on each of its sides high enough 
to carry the roof, while cross-beams proceed from the bottom of 
each king post under all the main bearers, so as to render the 
former, or any other trussing, nearly if not quite unnecessary. 
In fact, the principles of the common framed truss admits of so 



568 OF CARPENTRY. 

many modifications and applications, that it would be in vain to 
attempt to describe them all. 

1040. When the navigation of a river, or other causes, forbid 
the erection of piers in the stream, and it happens to be so wide 
that a truss might be unsafe, other modes of construction must be 
resorted to, and the polygon or arch are found the most effective; 
but in using these, a great additional expense is thrown into the 
construction, for a centring or support of some kind, to uphold the 
materials until the arch is completed, now becomes necessary, but 
was not required in any of the constructions before referred to. 

1041. Three distinct means are employed for forming this kind of 
bridge, viz: a series of hollow boxes, the sides of which that are to 
come into contact with other boxes, being inclined or sloping, so 
as to produce a wedge-like figure similar to the stones of which 
arches are formed. A series of stretching beams with a radial 
piece between each, and tye beams below, or a combination of 
bent timbers scarfed and joggled together, so as to produce a real 
timber arch. The platform or roadway of the bridge either passes 
over the whole of these, or is suspended between them. 

The principle of the first of these constructions is shown by Fig. 
240, in which it will be seen that these boxes are not made with 
close sides, but of the angles of boxes only, with cross braces to 
stiffen and strengthen them. By this means much material is 
saved and the construction rendered much lighter. This mode of 
construction requires so much good and expensive workmanship^ 
and introduces so many mortice joints near the ends of the pieces, 
being the most unfavourable positions for both strength and dura- 
tion, that on these accounts it is hardly ever used for wooden 
bridges, but it forms the leading feature in many that are made of 
cast iron, because in that material the angles can be cast solid 
and great strength obtained. This mode of construction will, 
therefore, be more fully described when we arrive at the subject 
of Cast Iron Bridges. 

1042. The second mode of construction is shown by Fig. 241, in 
which ab, b c, c d, &c. are stretching beams, made either of sin- 
gle or double beams abutting against radial pieces b e, c/, dg^ 
&c. called in this case bridle beams or pieces, the lower ends of 
which may proceed quite down, or very nearly down to a right 
line that would join the springings a and h; the lower ends of the 
bridle pieces are connected by timber or iron ties ae,ef,fg, &c. 
This framing is very simple and possesses great strength, while all 
the pieces are kept in a perfect plane with respect to each other, 
but the difficulty is to preserve this figure, since there is nothing 
by which this can be efTected, except the mortice joints, which, 



TIMBER BRIDGES. 569 

from the nature of the construction, must be shallow. In order, 
therefore, to use this framing with success, two of them must be 
used bolted or hooped together, and so arranged that the bridle 
pieces of the one truss may come half way between those of the 
other, in which case the straining beams will break joint, the joints 
of one set of pieces coming against the middles of those of the 
other set. By this means, and using several parallel ribs, con- 
nected together at proper distances, by diagonal struts disposed 
as in Fig. 242, a stitf and strong arch may be produced. The 
beautiful timber bridge over the Schuylkill at Fairmount, near 
Philadelphia, which was unfortunately destroyed by fire on the 
1st of September, 1838, offered a very fine and judicious example 
of such diagonal bracing. It was among the lightest, boldest, and 
most beautiful specimens of carpentry in the world, being a 
single arch of 340 feet 4 inches span, without any other support 
than what was derived from the two end abutments. 

The recent destruction of this bridge renders it desirable to 
preserve some record of its formation, and the construction of its 
framing is therefore shown by Fig. 243. It was designed by Lewis 
Wernwag, and one of its peculiarities was that every large piece 
of timber was sawed lengthwise in two, in order to examine its 
heart, and see that no rotten, shakey, or bad timber was intro- 
duced into it. By this means mortice holes were avoided in the 
main timbers, as the tenons passed between, instead of through 
them, but were let in a sufficient distance on both sides to pre- 
serve them in their positions. This expedient likewise proved a 
great preservative against dry rot, because all the timbers were so 
distant from each other as to permit a free circulation of air be- 
tween them, except in the actual joints, and they were kept close 
by iron screw bolts. There was a great quantity of bar iron used 
in this bridge; for the main arch consisted of three double rows of 
main timbers, laid three deep, or one above the other. Near to 
these, their corresponding halves were placed face to face, but 
with the tenons of what may be called the king posts between 
them, the whole being key joggled and bound together by wrought 
iron hoops. Twenty-nine king posts arose nearly in a radiant 
direction from the arch so put together; and side braces were ap- 
plied on each side of each king post, spreading to the full extent 
of the adjacent openings, and taking their abutments under 
shoulders near the tops of such posts, thus producing the crossing 
of the braces shown in the figure; and at each crossing or inter- 
section the braces were bolted together. Between the tops of 
every king post, a straining beam is introduced, thus preventing 
the tops of the posts from approaching each other; and conse- 
quently the arches below from changing their figure. The curva- 
72 



570 OF CARPENTRY. 

lure of the arches were further preserved by their extreme ends 
abutting against solid blocks of masonry built in the form shown 
in the figure, to receive them; and in order to give greater weight 
and stability to these abutments, they were carried considerably 
above the top of the springing of the arch; therefore the roadway 
instead of being directly upon the arches, was kept hollow or above 
them for the distance of six bays or openings before it intersected 
the general curvature, as shown by the dotted line a a. This floor 
was supported by transoms or cross pieces, bearing upon shoulders 
cut in the sides of the king posts, and bolted to them. A tye beam 
passed over the tops of every row of king posts to support them in 
their vertical and parallel directions, and to carry the roof with 
which this bridge was covered. It was also boarded up on the 
outsides so that none of the timber framing was visible, except 
from within. 

From the above described mode of framing, each space between 
one king post and another becomes a complete vouissoir or form 
similar to an arch stone; and a similarity may, at first sight, ap- 
pear between this arch and that shown by Fig. 240; but in that 
mode of construction each vouissoir or wedge is separate, while in 
this bridge they are all united by the timber arches, as well as by 
having only one king post in common to two of them. The artist, 
however, not willing to confide in the mere strength of the timber 
framing, tied the whole together to the abutments by a series of 
iron tye bars, commencing in the first instance by a bar h let a 
considerable distance into the stone-work of the abutment and 
there firmly fixed, and from thence passing to the top of the first 
post, and from thence down to the bottom of the second, c is an- 
other tye fixed in like manner into the abutment and passing to 
the top of the second post, and from thence to the bottom of the 
third; and these tyes, it will be seen, are continued from the top 
of one post to the bottom of the next, throughout the whole length 
of the bridge, meeting and taking an opposite inclination when 
they arrive at the centre, and contributing considerably to the 
strength of the whole structure. 

1043. Cross framing, by halving scantlings together and attach- 
ing them strongly to a top and bottom beam, or even to an inter- 
mediate one, as shown by Fig. 242, also produces a strong combi- 
nation against vertical pressure, and at the same time makes a 
most safe and efficacious side frame for bridges, and it is there- 
fore very commonly used for that purpose at the same time that 
it is affording suppport. The appearance somewhat resembles 
that of the framing of the Schuylkill Bridge, but its principle is 
different, and after what has been said on this subject, the student 



TIMBER BRIDGES. 571 

will have no difficulty in determining which of its parts are tyes 
and which struts, as well as seeing on what its strength depends. 

1044. When speaking of hooping beams or trusses together with 
iron, it must not be supposed that such hoops are in one piece, 
like those used in making casks, but they always consist of two or 
four pieces put together with screws and nuts, as shown at P and 
Q,, Fig. 244, which not only affords facility in putting them on, 
but likewise in tightening them at any future period, so as to ac- 
commodate them to any shrinking of the timber. 

1045. The third mode of construction is that in which the tim- 
bers are bent and scarfed, and so joggled one upon the other as to 
produce a real arch of timber. This is the mode of construction 
that has been principally adopted in the United States, which pos- 
sesses many bridges of this description of a magnitude and boldness 
of conception and execution, such as are met with in no other part 
of the world, Germany alone excepted. In contemplating these, 
one cannot help feeling a regret that such splendid works of art 
should be formed of a material so perishable as timber. 

Fig. 245 shows a small portion of the wooden arch that was 
adopted by Mr. Bludget in building a bridge over the Portsmouth 
river, being a single arch of 250 feet span. In this, the pieces 
forming the arch are not in contact, but twice their own depth 
apart, thus constituting three concentric arcs D E and F, of which 
that in the centre at E, and the corresponding arches in two other 
sets, support the floor of the bridge. These circular ribs were 
selected out of timber grown in a curved form, so as to insure the 
grain of the wood running nearly in the direction of the arch, and 
they are connected together by pieces of hard wood b and c, and 
a wedge a driven between them, mortice holes being made through 
the curved pieces for their reception. The curved pieces are fixed 
and secured at their proper parallel distances, by notches cut on 
the outer edges of the two pieces b and c, as shown by dotted 
lines at i, and the mortice holes have a corresponding shape. The 
wedge a on being driven brings all these joints into close contact. 
Each curved arc is composed of two pieces of timber, laid side by 
side, each piece being about fifteen feet long. These pieces are 
so disposed as to break joint, that is, the end of one piece comes 
against the middle of that which is contiguous to it. Their ends 
are not scarfed but abut in a close joint, one against the other, 
and the two pieces are jointed together by transverse dovetail 
keys and joints as before. The positions of the transverse keys 
and wedges are shown at /, and Fig. 246 is a horizontal view or 
plan of one of these joints on a larger scale. 

This is a very ingenious method of uniting work, and possesses 
the advantage of exposing every part to the free action of air, and 



572 OP CARPENTRY. 

permits any one piece to be taken out in case of its decay or 
failure, without disturbing the rest, which is a very material point 
to be attended to in the formation of all heavy framings exposed 
to weather: but the great number of mortice holes that are ne- 
cessarily made through the main ribs cannot fail to weaken them 
considerably, and would prove highly detrimental, if the pieces 
were otherwise strained than by compression. The keys and 
wedges being tightly driven in, supply the place of the wood ab- 
stracted, and, therefore, render the mortice holes less objection- 
able. But the bridge is stated to be very flexible, and would no 
doubt be much improved by the introduction of horizontal oblique 
braces, to connect the three ribs. 

1046. The most usual construction, however, is to place the 
timber arcs in contact with each other, and one of the simplest 
bridges of this kind is that at Wittengen, in Switzerland, slightly 
described by Mr. Coxe.* The principles of its construction are 
shown by Fig. 247. Its span is 230 feet, and although it rises but 
25 feet in the middle, it is found amply strong enough to sustain 
all the traffic that passes over it. It consists of two great timber 
arches approaching to the catenarian form, and fixed parallel to 
each other upon rock abutments, with the roadway suspended 
between them. ABC is one of these two arches built up of seven 
courses of solid logs of oak, in lengths of 12 or 14 feet, and about 
16 inches in thickness. These were picked of a natural shape 
suited to the intended curve, so that the wood is no where cut 
across the natural grain to turn it into shape. These logs are laid 
above each other in such manner that their abutting joints may 
be alternate, like those of a brick wall, simply built up by laying 
the pieces upon each other, taking care to make the abutting 
joints as close as possible. They are not fastened together by 
pins, bolts, or scarfings of any kind, but are held in their positions 
by iron straps or hoops, which surround them at the distance of 
five feet from each other, where they are fastened together by 
bolts and keys. The roadway is flat, or without any elevation in 
the middle, and is supported about the middle of the height of the 
arch, as shown by the line a h c, upon cross joists which rest on 
a long horizontal summer-beam hung to the bottoms of perpen- 
dicular pieces, which are bolted to the insides of the beams form- 
ing the arches, while their tops rise high enough to carry the 
plate d d, upon which the roof of the bridge is supported; the roof 
projects laterally over the arches to protect them from weather, 
and the three spaces between the uprights at each end have 
diagonal braces to assist the roof in withstanding the effects of 
wind. This bridge was the last work of Ulrich Grubenmann, of 

* Travels, Vol. L, page 132, 



TIMBER BRIDGES. 573 

Tiiffin, in the canton of Appenzel, an uneducated carpenter, who 
rendered hinnself celebrated by the erection of several large works 
of the same kind, and particularly the nnuch admired bridge over 
the Rhine at Schaffhausen, which he commenced in 1757, and 
finished in three years. 

1047. The Schaffhausen bridge had two openings, one of 193 
feet and the other 172 feet span, appearing to rest on a small 
rock near the centre of the river. When Grubenmann was 
applied to to erect this bridge, he was desirous of making it a 
single span of 365 feet from one side of the river to the other, but 
the magistrates deemed so large an arch in timber to be unsafe, 
and compelled him to take a bearing upon the central rock, 
which he unwillingly complied with. The bridge being finished, 
and publicly opened by the passage of loaded carriages, was 
declared to give complete satisfaction, and that being acknow- 
ledged, it is said that Grubenmann, in presence of his employers, 
took a thin board and passed it between the apparent abutment 
and the top of the rock, to show them that although it appeared 
to rest upon it, it did not in fact touch it, and thus that he had 
accomplished his desire of making it a single span. However 
this may be, it afterwards sunk by the compression of the timber, 
and took a solid bearing upon the rock, w^hich no doubt afforded 
very material assistance in its support. This bridge was much 
admired as a most excellent piece of carpentry, but owing to the 
oak beams that came in contact with the stone foundations being 
placed too low, and not being exposed to air, they rotted, and the 
bridge began to settle. Grubenmann being dead, it was repaired 
in 1783 by Georges Spengler, another ingenious carpenter of 
Schaffhausen, who raised the whole bridge by means of screw 
jacks, and replaced the decayed timber. This was the only 
repair done to it during the forty-two years it existed, and it 
would probably have been in good condition at the present day, 
had it not been burnt by the French army in 1799. This bridge 
was not composed of arches, but was on the principle shown by 
Fig. 236, viz: a number of diagonal struts or braces with strain- 
ing beams between them; but the roadway did not pass over the 
framing, but was suspended between separate parallel trusses by 
means of perpendicular tyes called stirrups, disposed at i i. Fig. 
236, united at their lower ends to straight beams m appearing 
like tye beams, but having neither a strain of extension or com- 
pression upon them, since their ends may hang free of the abut- 
ment walls, their only office being to support transverse joists 
upon which the planks of the road are fixed. 

1048. Whenever a bridge roadway is made of timber, it ought 
to be of two thicknesses of planking crossed, and so united together 



574 JOINING TIMBERS. 

that the upper one can be taken up without injury to that below; 
because the upper planking wears out rapidly from the passage 
of horses and wheel carriages upon it, and therefore often requires 
renewal, for which provision should be made without the necessity 
of disturbing the under planking, or any of the main timbers of 
the construction. 

When the roadway passes over the tops or crowns of w^ooden 
arches, and is required to be nearly level, it is best to support it 
upon joists which take their bearing upon perpendicular posts 
bolted at equal distances along the sides of the arches, or else mor- 
ticed into sleepers which pass transversely over the tops of all 
the arches, and take even bearing upon them all. 

1049. One great difficulty attending the construction of large 
timber arches arises from the lightness and elasticity of the mate- 
rial, in consequence of which, if a very heavy load is introduced 
upon a timber arch near to one of its abutments it may depress 
that part, thereby causing the opposite side to be elevated and 
change its figure; and although this effect may take place to so 
small an extent as to be invisible without close examination, yet 
it will rack and strain the joints, and cause them to become 
loose, and in time will prove very detrimental to the stability of 
the concern, and it must therefore be prevented as far as possible. 
Two methods have accordingly been adopted to meet this evil, 
one of which is to give much greater strength to the arch than is 
necessary for supporting the greatest load it may be expected to 
carry, by putting a great number of rings or arches of timber 
together in the manner already described; and the other is to use 
a weaker arch, and stiffen it by framing introduced within it, 
with a view to prevent the possibility of its changing its figure. 
The bridge built over the Delaware at Trenton, New Jersey, 
began in May, 1804, is of the latter description, and consists of 
five arches or openings extending across the river, which at this 
part is 1100 feet wide. It was designed and executed by Mr. 
Burr, is different from any timber bridge that preceded it, and has 
been much admired in Europe as a splendid specimen of construc- 
tion. The superstructure consists of five parallel rows of arches 
of wood, which are segments of circles rising from their chord 
lines in the proportion of 13 feet to 100. One of these is placed 
in the middle of the bridge, and the others respectively at 11 feet, 
and 4 feet 6 inches on each side; thus forming two carriage and 
two foot roads. The ribs or arches are all formed of white pine 
planks from 35 to 50 feet in length, 4 inches thick and 12 inches 
wide, except the middle one, which is 13. These planks are 
bent and laid one over the other in close contact, and with all the 
joints broken until they form a depth of three ifeet through, and 



TIMBER BRIDGES. 575 

they are secured together by iron straps. This method was first 
introduced by Mr. Burr, and is believed to possess advantages 
over the method of forming arches by whole timber. To guard 
against the springing or elasticity of the ribs, rows of horizontal 
tye beams are introduced from one pier to the other, and these 
are connected with the ribs by diagonal timbers, which are con- 
tinued above the spandrells of the arches, which are filled up 
with crossed or intersected timber in the form of diagonal braces 
connected with the roof plates, so that the ribs are stiffened both 
from within and without so effectually that it is next to impossible 
that they should change their form. 

The platforms on which the travelling is performed are sus- 
pended from these arches by means of perpendicular iron bars 
which hook into eye bolts firmly fixed through the arches, at the 
distance of every eight feet in the three middle sections and sixteen 
feet in the two exterior ones. To the lower ends of these bars stir- 
rups are appended, in which the beams lie that sustain the joists 
and flooring; diagonal braces are also used to connect the plat- 
forms with the tye beams, and thus prevent the swinging which 
they would otherwise be subject to. This bridge is supported by 
stone piers and abutments built so high above the highest rise of 
water as to place the structure out of danger from ice or freshets, 
and to permit the navigation of large craft beneath it. The whole 
is covered in and roofed so as to be effectually protected against 
weather. A general idea of the construction of this splendid 
bridge is given by Fig. 248. 

1050. Many other timber bridges might be described, but the 
specimens selected, it is believed, will cover every variety of con- 
struction, and our limits prevent a description of the details such 
as the manner of joining the timbers, introducing and fixing the 
bolts and iron work, and many other particulars which alone 
might fill a volume. These matters may be safely left to the 
judgment of the Engineer, when he has obtained clear ideas of 
the manner in which pressures will act and the best means of 
opposing them. But to strengthen his confidence in his own 
opinions and plans, it would be well that he should carefully in- 
spect, measure, and take drawings from some of the best bridges 
built, and of these numerous examples may be found in many 
parts of the United States. 

1051. The greatest load to which a bridge is subject, is when 
it is crowded by human beings, and such a load amounts to about 
120 lbs. to every square foot, independent of the weight of the 
bridge materials themselves, so that the actual load to be sustain- 
ed should not be considered less than about 300 lbs. for every 
square foot of roadway; and such strength ought accordingly to 



576 OP CARPENTRY. 

be provided in every bridge that occurs in great public thorough- 
fares. Timber bridge building for such situations has long since 
been given up in England, and will no doubt gradually die away 
in America also, but still they must always be used in certain 
positions and for certain uses; and the most frequent occasion that 
the Engineer will have for them is in what are called occupation 
bridges and shifting bridges in canal work. 

In the formation of a navigable canal, it very frequently hap- 
pens that the cutting may run through a portion of a man's estate 
or farm, thus cutting otFall communication between one part and 
another by the intervening water, and in such cases the land 
owner has a right to insist on the canal company putting him up 
such a bridge as shall enable him to have free access to, or occu- 
pation of his land. Such bridges not being on public roads, nor 
requiring any extraordinary degree of strength or elegance, are 
usually made of wood; and of course are maintained and kept 
in repair by the canal owners, unless a specific agreement is 
made to the contrary. When the canal is not in deep cutting, 
and its water comes nearly to the same level as the surface of 
the adjacent land, occupation bridges require considerable eleva- 
tion in order that boats with high loads may pass under them, and 
such constructions as are shown by Figs. 234 and 235 may be 
sufficient; but to render them available it becomes necessary to 
construct long hills or inclined planes at the abutments in order 
to obtain easy accessible roads to them. Such hills are expensive 
in their construction, dangerous in their use, and often unsightly 
and inconvenient; therefore shifting bridges are frequently used 
in place of them. These bridges are not raised up above the 
ordinary level of the land and roads, but they shift or move away 
in order to let highly loaded boats, or vessels with masts pass 
through them. 

1052. Shifting bridges are of two kinds, the drazo-bridge and 
the swing-bridge. The draw-bridge is merely a wooden platform 
of sufficient width to allow the passage of horses, wheel carriages 
and passengers, and of sufficient length to reach from one side of 
the canal or water course to the other, or rather to reach from a 
jetty or projecting abutment built on one side of the water to a 
similar projection on the opposite side, because when these bridges 
are used it is customary to contract the water passage to the 
smallest extent that will permit the necessary vessels to pass, in 
order to make the bridge platform as short and light as possible; 
for a platform strong enough to bear heavily laden wagons must 
necessarily be heavy. This platform is so fastened by pivots or 
hinges at one of its ends to the jetty or projection, that it can be 
raised from its horizontal into a vertical position while vessels are 



MOVEABLE BRIDGES. 577 

passing, and this is done in two ways. One of these is to attach 
a chain to each of the corners of the unhinged side, to lead these 
chains over two iron pullies fixed on the hinged side at a height 
exceeding the length of the platfornn, and to let them terminate 
at a cylinder or windlass, having a cogged wheel and pinion to 
gain power, fixed on the hinged side, for raising and lowering the 
platform by the turning of a handle. The other method is to fix 
a compound framed lever of wood or cast iron, shaped like Figs. 
249 and 250, over the platform b, such beam having strong iron 
pivots a a, which revolve on the tops of two posts fixed firmly in 
the ground at the two sides of the bridge, c c are two chains 
attached at their tops to the corners of the framed part of the 
lever, and at their bottoms to the sides of the platform rather 
beyond the middle of its length; and d d are two cast iron weights 
fixed on to the two arms of the lever for the purpose of nearly 
balancing the weight of the platform, and making it more easy to 
move. The platform should, however, have a preponderance, in 
order that it may lie steadily, when down, but the counterpoising 
weights assist materially in the ease and expedition of using the 
bridge, and are as important in lowering as in raising it; for if the 
platform is permitted to descend without counterpoise, it falls 
with a force that soon deranges itself, as well as the sill that is to 
receive it, and will stand in need of constant repair. When draw- 
bridges are long, or are subject to very heavy loads, the ribs or 
joists of which they are composed should be slightly cambered or 
bent upwards in the middle of their length like h, Fig. 250, and 
they should not only have bearing sills e e, to carry the weight of 
the bridge, but abutting sills f f. so framed and fixed that they 
cannot recede from each other, and be placed so far asunder that 
they may not pinch or confine the ends of the platform, but allow 
it a full half inch of play. A heavy weight coming upon the 
platform will, however, so far call the elasticity of the joists into 
play as to partly straighten the platform and cause it to take 
abutments from these beams at the same time that it is supported 
by those below. The balance drawbridge, from its simplicity, 
ease and expedition of working, is much more used than that with 
a capstan. 

When the canal or water course is very wide, two flaps or 
platforms, with separate apparatus for moving them, are hinged, 
one on each shore, and in this case they meet and abut against 
each other in the centre, and they must be curved and have good 
abutments on their land sides, to prevent them from spreading. 
Such drawbridges are very frequently introduced into the central 
or widest opening of stone, or other permanent river bridges, to 
permit tall masted vessels to pass through them. 
73 



578 OP CARPENTRY. 

1053. The swing-bridge is much more expensive in its con- 
struction than the drawbridge, but is very much used in canals, 
particularly for roads, when they are not sufficiently frequented 
to warrant the construction of a permanent brick or stone bridge. 
Their construction is such that the bridge never changes its hori- 
zontal position, but turns a quarter round upon a pivot, so that it 
may be turned over the water, or be pushed on one side so as to 
come over the dry shore. Fig. 251 is a ground plan, and Fig. 
252 a side view or elevation of such a bridge. In these figures 
a 6 is the width of the canal or water course to be crossed, and c 
d the timber platform, which generally has side rails for the pro- 
tection of passengers. The bridge, therefore, in appearance, is 
nearly similar to bridges of a stable construction, but by certain 
contrivances about it, it is capable of being turned from the posi- 
tion it holds over the water in Fig. 251 to that dotted in in the 
same figure. This is brought about by the means shown in sec- 
tion or profile in Fig. 252. e is a strong cylindrical pin or rod of 
wrought iron about three inches in diameter, its upper end being 
brought to an obtuse conical point, which should be of hardened 
steel, and its lower end is fixed into the centre of a cross f f oi 
timber or cast iron, best seen in plan in Fig. 251, (the same let- 
ters of reference being used in both figures). The iron pin is 
braced to the cross by diagonal pieces of iron spreading in four 
directions, so that it cannot shift its perpendicular position in 
respect to the cross. To fix the bridge, a pit or cavity is sunk 
close to one of the edges of the canal, and in this a solid and level 
foundation of brick-work or masonry is laid, as at g, Fig. 252. 
The top of this must be quite level, and be five or six feet below 
the intended surface of the bridge. On this the cross is placed, 
and is bedded in mortar in such manner that its iron pin may 
be correctly perpendicular. This adjustment being made, the 
cross and iron pin are built in with level and solid brick- work 
two or three feet high, so as to bury the cross braces and part of 
the pin, until about thirty inches or three ieet of its upper part 
can alone be seen. This is for the purpose of fixing the pin and 
giving it perfect stability. A flat ring of cast iron, at least six or 
eight feet in diameter, and perfectly smooth on its upper surface, 
which is six or eight inches wide, is next bolted down upon the 
brick-work by counter sunk bolts in such manner that the pin 
may be exactly upright and in the centre of the ring, the upper 
surface of which must be made truly level. The bridge itself is 
framed of three or four sticks of timber long enough to reach 
across the water, while they cover the iron ring. One of these 
pieces is shown at c d; they should have a slight camber upwards, 
and are attached together by being framed into strong end pieces, 



MOVEABLE BRIDGES. 579 

and are farther steadied and united by cross pieces between them, 
as well as by being planked over on the top. A transverse piece 
under c, Fig. 252, receives the top of the iron pin which works in 
a lump of brass or cast iron, with a conical hole fitted to the steel 
top of the pin. A strong timber frame h is supported by stand- 
ard i i below the bridge, and is floored or made close on its under 
side, which also carries another cast iron ring, or axle-trees like 
arms, for the cast iron wheels or runners to turn upon. These 
should be at least four inches in diameter, and are so adjusted as 
to height, that when the bridge is placed on its pivot, these 
wheels may just touch and run upon the upper smooth surface of 
the lowest cast iron plate; and to render the motion more steady, 
the iron centre pin also passes through a hole bushed with iron 
in a strong beam that runs across the frame h. Lastly, heavy 
stones, or blocks of cast iron ship ballast are piled up between the 
bridge and the upper roller plate upon the boarded frame A, the 
whole of them being disposed, as at /, behind the iron pivot e, and 
they require to be added until their weight exactly balances or 
counterpoises that of the projecting part d of the bridge; which 
done, a man with one hand will be able to swing or turn a bridge 
capable of sustaining the heaviest laden wagon with ease. The 
bridge being adjusted, all the moving parts are surrounded by a 
cylindrical brick wall like the wall of a well, reaching up to the 
ground height, and the wooden floor or platform of the bridge 
must oversail or cover this work, so as to hide it, and prevent, as 
far as possible, the introduction of pebbles, dirt, or any thing that 
might impede the moving par(s. A trap door should be formed 
in the bridge, or left through the brick-work, to admit a man to 
clean and grease the moving parts when occasion requires. The 
opposite end of the bridge is received into a large rebate made 
by two pieces of timber, seen in section at m and w, Fig. 252. 
These are of course placed on the opposite side of the water to 
the parts last described. The piece m takes the weight of the 
bridge, and for that purpose must be firmly bedded and bolted to a 
good brick, stone, or timber foundation, and n is an abutting piece 
for the bridge to shut against, which must of course be well stayed 
and supported in its place by nearly horizontal under-ground tim- 
bers resting against solid ground. 

The abutment sill n is not placed at right angles to the central 
line of the bridge, but inclines a little to it, as shown at n, Fig. 
251, and the end piece of the platform framework takes a similar 
direction, the object of which is, that the abutting sill may act as 
a slop to the motion of the bridge and only permit it to open or 
swing in one direction. The inclined direction also acts the part 
of a wedge, and causes the bridge platform, when it is shut with 



580 OP CARPENTRY. 

some force, to jam up and become quite tight, so that the bridge 
may not be subject to motion when a load is passing over it. This 
wedging effect might, however, prove detrimental by throwing 
the bridge off its pivot on the opposite side, but this accident is 
guarded against by the back of the framing i i having strong cir- 
cular ribs of timber fixed upon it; and these work about one- 
fourth of an inch clear of the inside of the circular brick-work, 
which is so supported on its back part as to offer a resistance to 
any motion. These bridges will occasionally set fast when they 
are closed or thrown over the canal, particularly when grit or 
pebbles get in between the wedge joint. A short post may, there- 
fore, be set in the ground with a lever or handspike to start the 
bridge from its wedging, and when that is done, it ought to swing 
so easily that a child may move it. 

1054. Swing-bridges are occasionally made wholly of cast iron, 
as at the shipping entrance to the London docks. In these bridges 
the roller plates of cast iron are fifteen feet in diameter, and all 
cast in one piece, and the great weight of these bridges renders it 
necessary to have chains and iron crabs, or tooth and pinion wind- 
lasses, to open and shut them. Such bridges are also made in two 
halves placed on opposite sides of the water, and are made to 
move in opposite directions, so that they meet and lock together 
in the centre. When double bridges are used they must be curved 
or half arched, with a slight rise in the centre, and in this form 
they require firmer abutments than have been referred to. This 
abutment is produced by long wedge-like pieces of cast iron, which 
are introduced between the moveable bridge and its solid abut- 
ments by a rack and pinion movement, and no load is permitted to 
go on to the bridge until they are put in their places. Of course 
they must be withdrawn again before the bridge can be moved. 

1055. Every swing-bridge and drawbridge ought to have a small 
chain fastened to it, of sufficient length to lie upon the bottom of 
the canal and extend to a post on the opposite bank, to which it 
should be fastened, for the purpose of closing the bridge from the 
opposite side when it is left open. Loaded carts and wagons are 
often detained for hours when they arrive on the shutting side of 
a swing-bridge, and happen to find it open. This evil is entirely 
removed by a sunk chain, which enables a man to pull the bridge 
over to him, if open, and affords no obstruction to the passage of 
boats, as the chain will always find the bottom of the canal. 

1056. The principles of carpentry already laid down apply to 
the construction of floors, partitions, frame buildings and roofs of 
every description; but we have yet to notice another important 
application of them, which is the construction of centring for the 



CENTRING FOR STONE ARCHES. 581 

support of arches while they are building, and with this we shall 
conclude the present division of the subject. 

Whoever contemplates the nature of an arch formed of bricks, 
stones, or other separate pieces of material, must be convinced 
that they could not be placed in the positions they are intended 
to maintain, without some artificial support for them to rest upon, 
until the arch is completed and made capable of supporting itself. 
And when that is done, this artificial support has to be removed 
in order to throw open the space, that has been arched over, with- 
out any impediment. 

This applies equally to all arches or vaults from the smallest to 
the largest, and the artificial support that is thus made use of, is, 
as a whole, called the centre, or more properly the centring of the 
arch, 

1057. In the construction of centring for small arches, little or 
no skill is necessary; and in all centring the two chief points to be 
attended to are, that its upper or bearing surface shall be very 
correctly formed to the figure assigned to it, whether it be a por- 
tion of a circle, ellipse, or any other curve; and that it shall be 
sufficiently strong to bear the weight of the materials the arch is 
to be composed of, together with the workmen, tools, and other 
things that may be placed upon it, without sinking or changing its 
form. The first is necessary, because as the bricks or stones are 
in succession placed immediately upon the upper surface of the 
centring, so of course the work, when finished, will exactly coin- 
cide with the form of such surface, and if any irregularities or 
inequalities exist in the centring, they will be transferred to the 
work, making it unseemly to the eye, and perhaps endangering 
its stability. The second qualification, strength and stability is 
necessary to the perfection of the first condition, because if a cen- 
tre is made in the most true and perfect manner before it is loaded, 
and from weakness or bad fixing it changes its form or position 
from the gradually increasing load that is brought upon it, it will 
have just as bad an efifect, or indeed worse, than if it had been 
badly formed in the first instance. Because bricks, mortar, and 
stone are inflexible materials, which admit of no change of form 
after they are set, without breaking. The first portion of work 
that is placed upon the centring will of course adapt itself, or will 
be adapted, to the exact form of the centre. But if by continuing 
the work and increasing the load, the centre is made to alter its 
figure, it may in the one case produce a thrusting or expanding 
force again the new work, and thereby cause its joints to crack, 
or it may sink or recede from that work and leave it without sup- 
port, which will cause its settlement, thereby destroying its sym- 
metry and beauty, as well as its stability. 



582 OF CARPENTRY. 

1058. Tlie principles of the construction of roofs already ex- 
plained apply with certain modifications to those of centres; but 
the centring for arches is subject to many more difficulties than 
roofs, and require the exertion of skill and judgment to guard 
against them. The roof is a fixed construction, which when once 
put in its place is never afterwards to be disturbed, therefore any 
necessary precautions may be resorted to for making it stable and 
secure. It has only to be covered with such slight materials as 
will resist the action of rain, snow, or heat; and consequently they 
are never very heavy, and whatever their weight may be, it is 
distributed with equality over the whole surface. No change takes 
place in the load of a roof, except that which arises from snow 
lying upon it, or perhaps, occasionally, persons standing upon it. 
With arch centring the case is quite different. The centre is not 
a fixed or stable erection, but is one that has to be moved and 
taken away, as soon as it has performed its office, and that with- 
out injury or disfigurement of the adjacent work; consequently it 
cannot be let into it, or form any part of it. The work or cover- 
ing that is placed upon it, so far from being light, is massive and 
heavy in the extreme; for, in the arches of large bridges, it is no 
uncommon case to have hundreds of tons of stone-work thrown 
upon the centre and depending wholly upon it for support. And 
the load cannot be equally distributed over the whole surface, be- 
cause it has to be built up gradually from its lowest to its highest 
point, and is, therefore, a constantly increasing series, incapable of 
aiding or supporting itself until the key-stones are introduced; and 
even then, although the arch may be capable of standing by itself, 
the centre is not relieved from its weight, until it is lowered, or 
permitted to recede from the superincumbent work. For these 
reasons the construction of a good and eflfective centring, and the 
manner of fixing it so that it shall be perfectly stable and firm 
while in use, and yet be easily lowered a small quantity without 
changing its figure or its original firmness and stability, and finally, 
that it may be entirely taken down and moved without injury or 
danger to the work built around it, is considered as one of the 
most difficult tasks the Engineer has to perform, and as a master- 
piece of workmanship in the artists employed in its execution. In 
fact, the beauty, stability, and duration of an arch constructed of 
proper materials and with good workmanship, is dependent en- 
tirely on the perfection of the centring upon which it has been 
built. 

1059. Every centre consists of two principal parts or elements. 
One is called the rib, and this answers the important part of deter- 
mining the form or curve of the arch and of giving strength and 
support to the whole fabric; and the other is the covering, or lag- 



CENTRING FOR STONE ARCHES. 583 

ging (as it is technically called), and consists of parallel boards, 
planks, or timbers, extending from one rib to another, or over 
several ribs according to the extent of the arch, and v^'hich is for 
the purpose of connecting the ribs together, and forming an ex- 
tended smooth surface, upon which the bricks, stones, or other 
materials of the arch are to be built and put together. 

1060. In small centres these parts or elements are usually nailed 
together and combined, so that the ribs and lagging constitute but 
one piece, and the whole is moved and set up together. But in large 
centrings, the weight and magnitude of the materials renders it 
necessary that they should be separate. Nay, even more, for a single 
rib of the centring of a large arch is so large and ponderous that 
it can seldom be moved in its entire state, but requires to be taken 
asunder, and carried in detached pieces to the place where it. has 
to be used, and it must there be put together or rebuilt, taking 
care to place it so exactly in its proper position that it will re- 
quire no alteration after its erection. Of course as many ribs as 
are needful will require the same treatment, and after they are 
all set up parallel to each other and adjusted so that their upper 
surfaces may bone perfectly in the direction of horizontal lines 
strained across them, and they are found perfectly out of winding, 
they are to be secured in their places by sloping or diagonal braces 
from one rib to the other, and then the lagging or covering may 
be placed and fixed upon them. 

1061. No centre can be formed even for an arch of a single 
brick, or nine inches in thickness, without two ribs, viz: one at 
each end of the lagging: and the additional number of intermediate 
ribs must depend conjointly on their own strength, and the weight 
of materials they have to support. This problem can only be 
solved by the practical skill of the Engineer, aided by the rules 
that have already been given for determining the strength of ma- 
terials, observing, in all cases, that it is better to err on the side 
of too much strength, than to trust to weak or nearly calculated 
structures. A large rib is always an expensive construction, but 
its first cost is nothing in comparison to the expense that will be 
incurred by its failure when in use, because if it sinks or changes 
its figure during the construction of the arch, there is no way of 
repairing the mischief that may arise, except that of pulling down 
all the previous work, strengthening the centre where it fails, and 
beginning the whole operation again. In large bridges it is cus- 
tomary to place the ribs parallel to each other and from three to 
six feet asunder, according to circumstances; and from what has 
already been observed upon them, it will be seen that their use 
and action is similar to the trussed principals of a roof; and as all 
the weight of the superstructure, including the lagging, is to be 



584 OP CARPENTRY. 

supported by the ribs, it will be equally evident, that the support 
of the whole centring, while it is in use, must be applied under 
the feet or abutment of the ribs and no where else. 

1062. In all regular arches, such as portions of cylinders, or any 
curves which have the same dimension throughout, all the ribs 
made use of must be precisely of the same size; and as the load 
of work to be placed upon them will be very nearly equal in all 
parts, when the arch is finished, so the ribs should be of equal 
strength. It follows from this, that any mode of construction that 
is adopted for one rib will equally apply to all the others made 
use of; and hence in describing centres, we shall adopt the usual 
plan of giving a description of one rib only, and saying how often 
that rib is to be repeated, keeping in mind that however long the 
arch may be, the lagging runs the whole length of it upon the 
curved surface of the ribs, and in most cases at right angles to 
them; consequently no particulars, except dimensions, will be ne- 
cessary in describing the lagging. 

1063. In some cases it may be necessary to construct what are 
CciWed Jlewing arches, or arches that are wider at one end than 
the other; or whose figure resembles a part of the superficies of 
a truncated cone. In this case the ribs must evidently not be of 
the same size, but must be formed with dififerent radii of curva- 
ture. One rib must be made for the large end of the arch, and 
another for the small one, and these being set up parallel to each 
other, or in such other position as the two ends of the arch are 
meant to have in respect to each other when finished, lines must 
be fixed and stretched upon the curved surfaces of the two ribs 
at proportional distances from each other, and these lines will give 
the magnitudes of any number of intermediate ribs which it may 
be thought necessary to construct and place at any assigned dis- 
tances between the two exterior ribs. The lagging must of course 
run in right-lined directions over the outsides of all the ribs, and 
will complete the conical or other diminishing surface which has 
to be given to the finished arch. 

1064. It may here be observed, that with the exception of 
building bridges of one or of two arches, there is no necessity for 
providing a quantity of centring equal in superficies to the quan- 
tity of arch to be constructed, because centres may be shifted 
and carried from one place to another, as the work proceeds, 
which saves a great expense. Thus in constructing a culvert or 
cylindrical drain for carrying water, or making a long vault or 
passage under ground between two parallel walls that have to be 
arched over, a centring of from six to nine feet long, or even less 
if the opening be large and the centring heavy, will be all that is 
necessary. This centring is first to be fixed in its proper place 



CENTRING FOR STONE ARCHES. 585 

at one end of the work, and the arch is then worked over its 
whole extent. That done, the centre is struck (which is the tech- 
nical expression for releasing and taking down centring,) and it is 
moved forward very nearly its own length, taking care to leave 
an inch or two of one of its ends underneath, but in contact with 
the underside of the portion of arch that has been built. In this 
new position it is to be made straight and level and again fixed; 
when a second quantity of arch work equal to its length may be 
built upon it, when it is again struck, advanced, adjusted, and fix- 
ed, and is ready for a third length of work, and by this process 
the arched vault may be continued any required distance with 
only one short centring. The only rule that can be given for its 
dimensions in such cases is, that it must not be so long or so heavy 
as to require any extraordinary exertion to move or refix it, be- 
cause, in these cases, there is generally not much room for action, 
and a danger of disturbing and breaking part of the former work, 
unless the shifting and refixing can be performed with great 
facility. 

1065. In building a brick or stone bridge, of a single arch, over 
a river it is obvious that we must fix the entire centring at once, 
before the arch is commenced, and likewise in building a similar 
bridge of two arches, where the meeting or springing of both 
arches rests upon a pier in the middle of the river, and the other 
feet of the arches abut on the banks, two centrings, one for each 
arch, will be necessary, and they must both be fixed in their 
places before the arch is commenced. The reason of this is, that 
if only one centre should be used, resting upon the bank or shore 
at one end, and upon the pier, in the centre of the river, on the 
other, and an arch should be constructed from one to the other, 
it would be impossible to strike and move the centring when the 
arch is finished, without endangering its downfall, unless the cen- 
tral pier is exceedingly strong. For so soon as the centring is re- 
moved the lateral spread of the arch will come into play> and as 
it will be incapable of acting upon the solid stone abutment, all its 
lateral expansive force will be exerted against the pier in the 
direction in which it is least capable of resisting pressure, and it 
will be overset. But by having the two centrings fixed at once, 
both arches will proceed at the same time — an equality of load is 
induced on the two opposite sides of the pier, and when the cen- 
tres are removed two thrusting forces, which are equal and dia- 
metrically opposite to each other, come into action at once and 
neutralize each other, and the pier, therefore, remains undis- 
turbed. 

1066. If a bridge of many arches has to be constructed, for the 
reasons above assigned, two centres onlv will be absolutely neces- 

74 



5S6 OF CARPENTRY. 

sary, though the use of a third will be advantageous. In this case 
the two or three centres of the arches of one end or abutment of 
the bridge are first fixed, and the land, or abutment arch is first 
commenced from both its feet or abutments, and in doing this a 
part of the second arch must also be commenced upon the first 
pier so as to weight it down, and at the same time to throw an 
equal weight on both sides of it, by which its stability is much in- 
creased; and this effect will be further augmented by also working 
up a small part of the second arch upon the second pier, so as 
to balance the second centring and prevent its sliding away from 
the lateral pressure of the load placed upon it. By judicious and 
skilful management the loading may be so arranged that the first 
or land arch may be completed, when its centring may be struck 
and carried to the position of the third or fourth arch as the case 
may be, and then the second arch from the land may be com- 
pleted, and in this way a bridge may be carried over a river until 
it arrives within two arches of the opposite side, when, if three 
centrings have been formed, one or two, as the case may be, can 
be fixed at once and worked up from the opposite shore to com- 
plete the w^ork. 

1067. This mode of proceeding does not often apply, because it 
is generally the case that the central arch of a bridge is larger 
than any of the others, and that they diminish in size as they ap- 
proach the shores; and whenever this is the case the centrings can- 
not be interchanged, except by commencing operations on one side 
of the river and then moving to the other, and so on alternately, 
until the meeting is made at the central arch. It was, however, 
adopted by Mr. Rennie, the English Engineer, in the construction 
of Waterloo Bridge across the Thames, in London, which consists 
of nine semi-elliptic stone arches all precisely alike, each rising 
35 feet and having a span or opening of 120 feet. The object of 
this similarity of dimensions in all the arches, is to obtain a per- 
fectly level road or causew^ay over the bridge, instead of ascend- 
ing and descending two hills or inclined planes, as is the case in 
most bridges. 

1068. It sometimes happens that arches have to be constructed, 
for the sake of their strength alone, in places where they will 
never be seen; consequently their symmetry and beauty is not 
important, and in some cases the introduction and taking away of 
centring might be difficult, or even impossible. Thus, for example, 
if a very large window or opening has to be left in a high and 
heavy wall, but which we require to have a straight or right 
lined, instead of an arched appearance, there is no way of doing 
this except by throwing a timber or stone lintel or breast-summer 
across the opening, and building upon it. That lintel may be con- 



CENTRING FOR STONE ARCHES. 587 

sumed by fire, may break, or will decay in time, and may thus 
endanger the wall. To guard against this we have only to build 
a quantity of work upon such lintel with a curved or semicircular 
termination above, but without any regard to the bond of the rest 
of the work, such curve springing from the perpendicular sides of 
the opening, or what is still better, from the extreme ends of the 
lintels. This work is to be used as a centring for turning an arch 
upon, and this is next to be done, when the wall may proceed up- 
wards upon the arch, just as it would have done upon the lintel; 
and it will be evident that where such a construction is resorted 
to, the whole lintel may decay, or may be taken away, as well as 
the quantity of work that was used as centring, because now the 
arch will sustain the load instead of the lintel, and a new lintel 
can at any time be introduced. 

1069. It frequently happens that arches are necessary for the 
support of the underground foundations of walls and other erec- 
tions, and which might not be able to bear the great expense of 
regularly framed centring. Thus in digging the foundation for a 
long wall, the soil in general may be hard, solid, and trustworthy, 
but we occasionally meet with soft places, arising from springs, 
quicksands, or the ground having been before dug up, or recently 
made level, which would render it unsafe to carry the wall over 
them, and in this case it may be necessary to turn an arch from 
one hard place to another, thus passing over the soft and insecure 
places. This may generally be done by an earth-centre ^ i. e. by 
having a concave curved mould or pattern, formed out of thin 
plank to the shape we wish to give the arch, and then digging up 
and forming the ground so as to fit the curve of the mould. The 
earth so shaped must be well and solidly rammed down until the 
desired curve is obtained, and then a brick or stone arch may be 
built upon it just as well as upon a regular centring made by the 
carpenter, and upon the top of this the wall may proceed upwards 
with perfect security; for if the soft soil sinks away from under the 
arch, it will only be the same thing as taking the timber centre 
away from an arch constructed by the regular process. 

1070. This mode of centring is constantly resorted to for cover- 
ing over furnaces, bakers' ovens and cinder or coke ovens, the 
tops of which are an irregular kind of dome, which would be diffi- 
cult to construct in carpentry. But the side walls being carried 
up perpendicularly, the body of the oven is filled with damp sand, 
which is raised up in a convex form to the exact shape the dome 
is intended to have, and the bricks are then laid as over any other 
centring. When sufficiently dry and set, the sand is dug away and 
moved through the door or mouth of the oven. 

1071. After these preliminary observations we will proceed to 



588 OF CARPENTRY. '"'* ' 

describe the principles and construction of centring, as it is used 
and applied to the purposes above mentioned. 

All centring is made of timber, strengthened where necessary 
bj wrought iron straps and cast iron bearing plates, and the ribs 
are usually put together with wrought iron screw bolts with nuts 
and washers, for the facility of taking the parts asunder, and re- 
building them when they have to be erected or moved from one 
place to another. In this respect they differ from roofs, which 
may be permanently pinned or nailed together, because they 
are not intended to be moved after they are once fixed in their 
places. 

1072. Small centres are generally made of two, three, or more 
ribsj with the lagging permanently nailed to their convex surface. 
The ribs should always be formed of two or three thicknesses of 
board or plank nailed together, with the grain of the wood cross- 
ed, or placed in such directions that one piece may assist the other 
in strength, and the lower part of the centring should be right 
lined, forming a diameter or chord to the curve above it, for the 
double purpose of making a tye to prevent the curved surface from 
opening, and also of affording a flat surface upon which the cen- 
tring may stand and be supported in its work. 

1073. In the formation of large centring for bridge building such 
constructions would be ineffectual, and we must have recourse to 
the principles of carpentry already laid down. The first and chief 
rule to be attended to, is to dispose every piece in such manner 
that it shall be subject to no strain, but what either pushes or 
draws in the direction of its length; and in all timber constructions 
the pushing or thrusting strain is decidedly superior in advantage 
to the pulling one; for when the straining force tends to draw a 
beam out of its place, it must be held there by a mortice and 
tenon, which possesses very trifling force unless when assisted by 
iron straps and bolts. Cases occur where it may be very difficult 
to make every strain a thrust, and the best constructors there- 
fore admit of tyes; and, indeed, where we can admit of a tye beam 
connecting the two feet of our frame, we need seek no better se- 
curity. But this is often inconvenient or impracticable. Should 
the river be navigable, such a beam would effectually stop all 
craft from passing up or down it, and as all rivers are more or less 
subject to freshesj it would occasionally be under water and liable 
to be carried away, and with it all the work above it, thus pro- 
ducing destruction of the most fatal description. 

1074. With a view, therefore, of avoiding the danger of floods 
or freshes, and to permit the uninterrupted passage of trees, logs 
of wood, ice, and other matters that may float upon a stream, it 
is advisable to dispense with the use of a transverse or tye beam, 



CENTRING FOR BRIDGES. 589 

and to keep the whole of the centring as high up out of the water 
as may be possible, without occasioning inconvenient slopes in the 
roadway over the bridge. Indeed, if a river is navigable, this ele- 
vation of the centring becomes absolutely necessary, and by con- 
sidering and applying the principles of constructive carpentry, it 
will be found that abundant strength may be obtained without 
descending any very great distance below the underside of the 
arch; and, consequently, that ample space may be left for the 
passage of boats and other craft under an arch while it is in pro- 
gress of construction. To form such a centring well, requires 
great judgment, and a scrupulous attention to the disposition and 
operation of all the pieces; for it is by no means an easy task, even 
for the experienced, to discern whether a beam that makes part 
of a centre is in a state of compression or extension. In the con- 
struction of a good centre, we have a number of separate pieces 
of timber all conjoined to produce two common effects, which are 
strength and stiffness, or immutability of figure. No piece should 
be introduced into this combination but what has a duty to per- 
form, otherwise we should load the centre with additional weight, 
without a corresponding benefit; and all the pieces should be so 
disposed as will enable them to perform their duties with the 
greatest possible effect, or in other words, to be subject to longitu- 
dinal compression whenever it can be obtained, or to longitudinal 
extension, as the next best thing, when the first is impossible. 

Every disposition likely to produce lateral pressure, and conse- 
quent bending of the pieces, must be carefully avoided, and the 
artist must not only be able to design and put his pieces together 
so as to produce these effects, but to judge by his eye-inspection 
and reasoning powers what effect they will have on each other — 
which will become compressed and which extended pieces — what 
the consequence of any piece giving way may be, and how it will 
affect the general structure of the whole; how defects may be 
strengthened or repaired, and if the whole is secure and immuta- 
ble. 

1075. The experienced artist will, in general, be able to judge 
of all these points by an accurate drawing to scale, in which the 
dimensions of the several parts and the materials made use of are 
noted down. But this cannot be expected in the young and un- 
practised. If therefore he should be called upon to carry works 
of this kind into execution, his safest plan will be, not to attempt 
any thing original, but to take advantage of the experience of 
others, and copy that which has been already done and found to 
answer its intended purpose. Here he will find the value of that 
precept laid down in a former part of this treatise (5), viz: the 
taking sketches and memoranda of the dimensions of materials 



590 OF CARPENTRY. 

and mode of putting them together of every thing he meets with 
that may be Hkely to occur to him in the progress of his profession. 
He will find a collection of such memoranda sketches or drawings 
of infinite use to him. If, however, he should be tempted to try 
his skill on an original design, it will be very advantageous not to 
trust solely to drawings, but to have a model made to scale, and 
to try the effects of weights disposed upon it as nearly as may be 
in the same places as the load will occupy on the large or actual 
construction. He will then, by the examination of the joints, be 
able to see which pieces are compressed and which extended. For, 
as before observed, this effect is sometimes difficult to ascertain in 
a drawing, and the experiment cannot be tried on a large scale 
upon the centring itself or even upon one of its ribs. They are 
so large and massive that no weights we could place upon them 
for experimental purposes would make the least impression, or 
bear any sensible proportion to the immense load of stone they 
are destined to bear when the arch is under construction: and the 
building of an arch is too expensive an operation to be considered 
an experiment. If a failure occurs, the arch is gone, and with it 
most probably the future reputation and fortune of the young 
artist who may have attempted it. 

1076. We cannot have a stronger proof of the truth of this as- 
sertion, than our finding pieces introduced as struts (and having 
considerable dependence placed on them as such) in the designs 
of some of the most eminent Artists and Engineers, while in fact 
these very pieces are performing the part of tye beams, and should 
be secured and treated accordingly. Of this the much celebrated 
centring used for the stone bridge over the Loire, at Orleans, in 
France, as designed byM. Hupeau, in 1750, is an example. This 
bridge consists of nine semi-elliptic arches, the central one rising 
30 feet, and having a span of 106 feet, and the end arches rising 
28 feet, with 98 feet span. It is justly considered one of the most 
simple, elegant, and beautiful constructions of the kind that has 
ever been executed, and the centring used is described with ad- 
miration by all who speak of it. Still it was materially defective, 
as we shall afterwards see. The disposition of the timbers in this 
centre are shown at Fig 253, PI. VIIL, where it will be seen that 
its main timbers form parts of two polygons which are not paral- 
lel and concentric. They each offer five sides for the support of the 
work, and they are connected together by five strong tyes, with 
bridles or connecting pieces, which divide the entire rib into three 
trapeziums and two triangles. The central one has a king post 
and two diagonal braces. The two next adjoining have diagonal 
braces only, and the two narrow or triangular end spaces are 
connected by bridles only. The regular curvature for the arch is 



CENTHINO FOR BRIDGES. 591 

obtained by a curved timber a a passing over the whole rib in the 
same plane, and supported by blocks of timber between its under 
side and the upper sides of the polygon; and upon the top of this 
curved piece, called the arch mould, the timbers of the lagging 
are supported. This latter piece, with its blockings, has nothing 
to do with the strength of the rib, and is merely introduced to 
obtain regularity of curvature; all the strength must therefore 
be sought in the double polygon and framing below. This con- 
struction is on sound principles, provided we are certain that no 
change of figure can possibly take place, and the formation is 
beautifully simple, consisting of very few parts, and those of great 
magnitude; for each face of the polygons was upwards of 20 feet 
long, and the beams were 15 inches square. It therefore well 
deserves the character that has been given of it by those who 
have written upon this subject, as being one of the boldest 
attempts that has ever been made at this species of construction; 
but M. Hupeau appears to have been mistaken in supposing that 
both the upper and lower polygons would equally assist in sup- 
porting the load, and would be both thrown into a state of com- 
pression by it. This would have been the case, if the stone arch, 
which was six feet in thickness, could have been thrown over the 
whole centring at once, and thus have occasioned an equality of 
pressure over the whole at the same moment; because in that 
case, both the polygons would have been thrown into a state of 
compression, and one would have assisted the other. But masonry 
and brick-work are slow and progressive in their operation, and 
must be began from the bottom and carried upwards. The pres- 
sure, therefore, came upon the centring at its two feet or spring- 
ings, and proceeded gradually upwards. The consequence of this 
was, that the centre changed is figure by the two haunches or 
springings sinking down, which had the etTect of raising the crown 
or central part. Now, as the sides of the lower polygon were 
shorter than those of the upper one, they could not give way to 
the same extent, and the consequence was, that they were drawn 
away from their end attachments, and thus it was found that the 
lower polygon, instead of being in a state of compression, as was 
intended and expected, was in a state of expansion, and that its 
place would have been much better supplied by a series of iron 
bars, with screw nuts at their ends to tighten them, and make 
them act as tyes; for this turned out to be the sole operation of 
the lower polygon. The whole load was consequently carried by 
the upper polygon, and the wonder is, how an arch could be con- 
structed at all upon such a centring. M. Hupeau, who designed 
this bridge and its centring, began the work, but died before it 
was much advanced. The completion of the bridge then fell into 



592 OF CARPENTRY. 

the hands of the celebrated French Engineer Perronet, and the 
trouble and difficulty he had in building the arches upon these 
centres will be noticed with more propriety in our next chapter, 
which is devoted to the building or construction of arches, and 
the simple, yet efficient contrivance that he resorted to for ren- 
dering these centres stable and effective, will then be described; 
and then it will be better understood, because we shall previously 
proceed to an examination of the principles upon which the 
strength of centres depend. 

1077. It is obvious from what has been observed in the previous 
statements, that the strength and stiffiiess of all framing will de- 
pend upon the triangles into which the work can be resolved. 
And that the strain which one piece produces on the others that 
meet it in one point, depends on the angles of their intersection, 
and is greatest in obtuse angles and less in those that are acute, 
diminishing in proportion to their acuteness; and this suggests at 
once the general maxim, that in the construction of centres, as 
well as all other strong framing, we must avoid all obtuse angles 
as far as possible; and this conjoined with the principles that in 
every case where it is possible we must obtain longitudinal com- 
pression, or if this cannot be had, longitudinal extension. That 
we must in no case exert lateral pressure without an opposite 
countervailing force to oppose and equalize it, and we have all the 
general rules that apply to this subject. 

1078. The ancients do not appear to have laid down any 
precise rules for the construction of roofs, and as the arch is a 
more recent invention, no general and distinct views for the con- 
struction of arches or their centrings were laid down until the 
beginning of the eighteenth century. Figures are preserved of 
the framework or centring employed by Michael Angelo in the 
construction of St. Peter's Church, at Rome, w^hich is by far the 
largest christian church that has ever been erected in the world. 
It is surmounted by a dome of immense magnitude, but the cen- 
tring used is said to display very little skill or science, and those 
for the arched roof of the church itself although better, are far 
inferior to others that have been employed in later times. 

Sir Christopher Wren, an English architect, who died in 1723, 
and who stands pre-eminently distinguished as a philosopher, 
mathematician, and man of highly cultivated taste, was extensive- 
ly employed in his profession in England, and constructed many 
of her noblest works, and among others the justly celebrated 
Cathedral of St. Paul, in London, introduced many improve- 
ments into the art of building. But unfortunately though his 
architectural works remain, and his literary ones are preserved, 
that does not appear to have been the case with his practical and 



CENTRING FOR BRIDGES. 593 

executive modes of proceeding, or we should most probably have 
seen in them every thing that science, skill, and practice could 
suggest. We are told that his centring for the dome of St. Paul's 
Cathedral was a wonder of its kind; begun in the air at the height 
of 160 feet from the ground, and without making use even of a 
projecting cornice lo rest it upon. 

1079. The earliest centring that is described as being construct- 
ed upon scientific principles is by a French Architect M. Pitot, 
and it is so simple, and at the same time embraces so many of the 
points that are essential to the construction of a good and perfect 
centre, that its examination makes a very proper subject to com- 
mence upon. Its disposition for a semicircular arch is shown by 
Fig. 254. 

This centre consists of two parts, an upper and a lower. The 
upper part is all that is above the horizontal stretcher or tye 
beam A A, and the lower part all that is beneath it. The upper 
part is a common roof truss with a tye beam and king post, but 
having two principal rafters instead of one on each side. The 
exterior rafter 6 is carried out as far as possible, consistently with 
its having a sufficient quantity of timber to abut against at the 
top of the king post and end of the horizontal stretcher. The 
distance between the king post and the insertion of this rafter into 
the stretcher is equally divided, and that point gives the proper 
place of insertion for the shorter or under rafter c on both sides of 
the king post; while its upper end has to be inserted as far up the 
king post as possible, not to interfere with the insertion of the 
upper rafter. The whole of this truss is next to be supported in 
the intermediate position of the arch which, it will be seen by the 
figure, is more than half way up from the horizontal line or spring- 
ing. To obtain the position of the main stretcher A A., divide the 
whole semicircle into four equal arcs of 45° each, and 45° from 
the springing on either side will give the positions for the two ends 
of the stretcher, and the two remaining arcs of 45° or 90° will be 
occupied by the top truss. The support above referred to is ob- 
tained by four oblique struts, two on each side, as d e, df. Their 
two feet d may be close together and likewise close to the exte- 
rior arch mould, (not yet described,) and the whole must be sup- 
ported below on a sole or block g of hard compact timber, into 
which they are sufficiently let in to prevent their slipping or 
changing their positions, but not so deeply as to maim or weaken 
the soles. The soles are, in their turn, placed above other pieces 
of similar timber parallel to, and, if possible, larger than them- 
selves, called beds, and between the bed and sole polished cast 
iron or hard wood wedges are introduced, so as to separate the 
bed and sole to a distance of from six inches to a foot or more 
75 



594 OF CARPENTRY. 

from each other, according to the magnitude of the arch. Great 
care is necessary in the construction, selection of materials 
and placing of these wedges, because the whole weight of the cen- 
tring and its superincumbent work rests upon them; and their 
use is to adjust the centre as to level and height, and afterwards 
to strike it when the arch is finished; because by striking upon- 
the small ends of these wedges they may be made to retire in any 
necessary degree, or may be wholly withdrawn, when the soles 
will come into contact with the beds, and of course the entire 
centre will fall and retire from the arch, when it can be taken 
to pieces for removal. The oblique struts d e, df, being thus well 
secured at their lovver ends, are made to diverge to such an ex- 
tent that they may be let in to the under side of the main 
stretcher A A, exactly opposite to the abutments of the feet of 
the long and short rafters, so that their action is immediately 
transferred and carried up to the king post. But if the arch is 
intended to be large, it is advisable not to let the two internal 
struts d f into the main stretcher at all, but to cause their 
upper ends to abut agjainst the two ends of a horizontal strain- 
ing beam h bolted with iron screw bolts to the lower side of the 
main stretcher, as shown in the figure, and this will not only afford 
an effectual support to the upper ends of the internal sloping 
struts, but will give strength to the main stretcher in that part 
where it most requires it. So far we have only considered the 
trussing work which is to give strength to the rib, without show- 
ing how the curved form for the arch is obtained, and this is the 
only objectionable part of the construction as laid down by M. 
Pitot. The curve is obtained by an exterior string of timber 
which surrounds the truss and is called the arch mould, because it 
must be cut to the exact form the inside of the arch is intended 
to have when finished. The arch mould is of the same thickness 
as the rest of the rib, but instead of being formed of solid timber 
like the other pieces, it is formed of two, and sometimes of three 
thicknesses of plank fastened together with tree-nails and iron 
screw bolts, the joints being in the plane of the rib, or in a verti- 
cal direction when the centre is set up for use. The reason of 
this is that by so combining thinner timber, great waste of mate- 
rial is obviated and additional stiflTness obtained by the frequent 
crossing of grain. The arch moulds in this centre have but five 
principal abutments or points of support, viz: one at the top or 
crown, upon the top of the king post; two upon the ends of the 
main stretcher A A; and tvi^o at the bottom upon the soles ^^. 
All the intermediate ones are obtained, by the double cheeks or 
bridles i i i. These are called double, because they consist of two 
pieces placed opposite to each other on the two sides of the rib. 



CENTRING FOR BRIDGES. 595 

and they are notched down or halved upon the several pieces 
thev pass and intersect, and these two halves are drawn together 
by iron screw bolts, by which means, if the shoulders are well and 
efTectually cut, they fornn excellent braces to stitFen the straight 
pieces they intersect. Still their position and action is quite at 
variance with the principles laid down, since their effect will be 
to produce lateral instead of longitudinal pressure, a thing con- 
stantly to be guarded against. In building the arch, the weight 
of the masonry is wholly supported by the exterior arch mould, 
and it will have a tendency to sink; that tendency is transmitted 
directly by the bridles to the rafters of the upper truss, and to the 
oblique braces which support it below, and transmitted in the 
worst possible directions, or nearly perpendicular to the longitudi- 
nal direction of these pieces, or where it has the greatest power 
to bend them; and if they do bend, the strength and correct figure 
of the whole centre is gone. It happens, however, that a very 
easy and effectual remedy may be resorted to for obtaining all re- 
quisite strength in the upper truss, and it is astonishing that this 
did not occur to M. Pitot, but he does not mention it. Instead of 
letting the bridles be cut short at their lower ends so as to rest 
upon the rafters, we have only to lengthen them, and let the two 
central ones take their abutment upon haunches in the king post 
at its two sides. Another pair of bridles may be so introduced 
that they may extend down to the main stretcher at the point of 
intersection of the straining beam and inner oblique strut, and a 
very effectual support will be obtained, and an intermediate bri- 
dle may be introduced and be extended down to, and be made to 
bear upon the main stretcher at a point where it is well support- 
ed upon the straining beam, and then the upper truss will be ren- 
dered exceedingly strong. 

In the lower compartment we have not the same advantage, 
because there is no means of stiffening or supporting the oblique 
struts against the lateral pressure thrown upon them, except by 
introducing long beams that shall extend to the opposite foot of 
the arch, and they would not only impede navigation, but would 
be too long to afford effectual support unless they were trussed 
to prevent their bending. The lower pair of diagonal struts may, 
however, be materially assisted by two iron tye bolts reaching 
from near their centres to the extreme end of the main stretcher 
above, and to the upper strut and arch mould near their feet on 
the sole. This precaution is, however, seldom necessary, as we 
shall see in our next chapter, because in the semicircular arch, 
the lowest 30° has very little of the weight of the arch to support, 
and the load only becomes oppressive as it approaches the crown, 
and in this centre the strength is abundant as soon as we have 



596 OF CARPENTRY. 

surmounted the first 45° and got upon the upper truss, which is 
very strong. This centre is not, however, given as a model of per- 
fection, so much as to explain the nature and action of a trussed 
rib; and as we advance further in the subject we shall see how 
these difficulties must be met. 

For the sake of keeping the figure as simple and intelligible as 
possible, the cheeks or bridles are only shown in one half of the 
arch, and the other half exhibits nothing more than the naked or 
unincumbered truss; but it must be kept in mind that in the com- 
plete centre, whatever occurs in one half, must also be introduced 
into the other; and that the two halves of the semicircle must be 
perfect counterparts of each other. It may likewise be here 
noticed that although this centre has been described for building 
a semicircular arch, it is equally applicable to the construction of 
a smaller arc of a circle, or to a semi-ellipse, with a very slight 
modification of its parts. For a smaller arc or segment of a cir- 
cle, such for example as would occur if we imagine the springing 
of the arch to take place from the dotted line k k instead of the 
diameter, every thing would remain without alteration except 
the lower oblique struts d e, df, and these would have to be so 
placed that they would make more acute angles with the hori- 
zon. But they must in no case be so far sloped as to cause them 
to pass beyond the direction of the right lined direction of the 
rafters, if prolonged and drawn upon them. To adopt this cen- 
tring to an elliptic arch, no other alteration v^rould be necessary 
than to give the arch mould the elliptic instead of the circular 
form. The king post would become rather shorter, and the main 
stretcher somewhat longer in the elliptic than in the circular arch, 
and as height of king post is essential in order not to give too ob- 
tuse an angle to the rafters, this may be obtained without detri- 
ment by giving the main stretcher a lower position than has been 
assigned to it in the circular arch — with these exceptions every 
thing else will remain the same. 

1080. The manner in vvhich a centring springs from its soles, 
and of supporting those soles upon the beds, has already been re- 
ferred to, but no notice has yet been taken of the manner of sup- 
porting the beds upon which the whole stability of the centre 
depends. In Pitot's figure the centre is represented as resting 
by both its feet upon a projecting moulding below the spring- 
ing of the arch, as shown in our figure 253; but this would not 
answer in practice except for small and light arches. Projecting 
mouldings are introduced into constructions for ornament alone, 
and seldom with any view to strength: consequently if we were 
to trust our centring upon them, there can be little doubt but that 
in most cases we should break away our ornaments and obtain 



CENTRING FOR BRIDGES. 597 

no stability for the centre. The firm fixing of the beds is, there- 
fore, an object that requires the utmost care and skill of the 
Engineer, because however good and perfect a centring may be 
it will become non-effective unless well fixed. For this purpose 
rows of piles are very frequently driven between one pier and 
another, and as close as possible to them, but this is not a good prac- 
tice, for the load of a large centre with a nearly finished arch 
upon it is so enormous that piling can hardly be trusted to carry 
it. The piles may bend or sink deeper into the ground than was 
intended, and derangement must certainly follow, besides which 
driving a number of piles near the foot of a pier may disturb its^ 
foundation and future stability. The safest way, therefore, that 
can be adopted, is to support the beds upon strong vertical story 
posts with oblique braces, the bottoms of which rest on the offsets 
or footings that are constantly made, and which may be left wider 
than would otherwise be necessary, near the bottoms of the 
stone or brick piers, and to drive no more piles into the ground 
than are necessary for the purpose of supporting braces to hold 
these story posts in their proper vertical position. In this manner 
no vertical weight is brought into action upon the piles, which may 
therefore be comparatively weak, and need not be so driven as to 
endanger the foundations of the piers. The whole load is thus 
thrown upon the piers, and nothing can sink unless they go down, 
and should that be the case of course the whole bridge will be in 
danger. In order to give additional security to the beds, their 
foundation is made continuous and connected throughout the 
whole width of the arch, and it thus becomes a regular platform 
braced from end to end, while the bed blocks alone project from 
its upper surface, which may be floored for the convenience of 
getting at the wedges. The soles, on the contrary, are not con- 
tinuous, but a separate one is applied to each foot of each rib, and 
these stand upon the projecting blocks of the bed platform, so that 
workmen can readily get at the wedges to use sledge hammers 
upon them in case they should require alteration, and in this man- 
ner the several ribs of the centre can be adjusted with the great- 
est nicety. 

1081. The great trouble and expense that is incurred in pro- 
ducing a good and sufficient bed platform may be better judged 
of from inspecting Fig. 255, which is a sketch of the centring and 
progress of the new London Bridge, as constructed by Mr. Rennie, 
as it appeared early in the year 1828. Each arch was supported 
by nine parallel ribs, of the construction shown in the figure, 
placed six feet apart, and supported by an under framing extend- 
ing one-third of the span of the arch, on each side, independent of 
the oblique braces, and the whole carried by a scaffolding of 



598 OP CARPENTRY. 

whole square timbers, crossing each other, and resting on piles 
driven to support them. 

1082. Allusion has been before made to the centring used 
by Michael Angelo in the construction of the body of St. Peter's 
Church, and it will be found that it approaches very nearly to the 
principles laid down by Pitot as already described, but is superior 
to it; for the pieces are judiciously disposed, and every important 
beam is amply secured against all transverse strain. The only 
fault that has been found with this design is, that it is unnecessa- 
rily strong. Its general disposition is shown by Fig. 256. After 
what has been said of Pitot's centre, no particular description of 
this can be necessary, further than to observe that while Pitot's 
centre is mentally resolvable into two parts, this really consists of 
two separate and distinct formations, for the upper part is a regu- 
lar roof truss with a separate and complete tye beam, which rests 
upon what may be called a collar beam, or flat top to the under 
truss, and these two are not connected in any way, but a row of 
cross wedges may be introduced between them for the purpose of 
lowering or even striking the upper truss, without at all disturb- 
ing the one that is below it, which is often a great advantage in 
the construction of large arches. It will be apparent to any one 
that the lower polygon a g ihh and its stretcher or collar beam 
g h, are useless and superfluous in this centre. Because if the 
king post does its duty, it is impossible that the middle of the tye 
beam can sag or drop, and its two ends are equally well support- 
ed by the nearly vertical struts k k, while its intermediate parts 
are upheld by the more sloping struts / /, none of which can shift 
from their places if properly framed. The only chance of danger 
is from the external walls or abutments at a 6 opening outwards, 
and this must be guarded against in their own strength, or by ex- 
ternal support, or an additional tye beam between a and h. The 
lower polygon would not at all help or remedy this evil, because 
if the abutments should spread, the polygon would open and cease 
to be of any use at all. 

1083. Having shown the form and disposition of some of the 
simplest kinds of centring, we will next examine a few of more 
complex construction; but previously to doing so, a few observa- 
tions on the means of determining the strength and power of cen- 
tres will be useful, and the form of M. Pitot's centre, as given in 
Fig. 254, affords a very good example, because in describing it, 
he gives the scantling or dimensions of the timber to be used for 
constructing the ribs of an arch 60 feet in diameter, presuming that 
the ring of stone-work, which is to constitute the arch, is 7 feet 
thick, and that each cubic foot of stone weighs 160 lbs. The en- 
tire weight of stone, that each rib will have to carry, according 



CENTRING FOR BRIDGES. 599 

to this computation, will be 707,520 lbs. The thickness of the 
stone ring is, however, much greater than can be necessary in an 
arch of so small a span, for half this depth, or from 'S^ to 4 feet of 
stone would be ample, and would, of course, permit the rib to be 
made much slighter than the dimensions he has assigned to it. 
We shall, however, pursue the investigation in his own terms. 

1084. It has been before observed, that in the semicircular 
arch, very little of the weight of the stone, which forms the lowest 
30° on each side of the arch, is felt by the centring, because the 
lowest stones are so superposed that they support each other; and 
when they do begin to lean over, the friction upon their bedding 
joints prevents their sliding forwards so as to press with much 
force against the centring. On this account a considerable deduc- 
tion from the weight of the entire ring of stone has to be made 
before we can determine the pressure exerted upon the rib, and 
M. Pitot computes that this diminution is equal to y^ths of the en- 
tire load; consequently we shall only have to provide for the sup- 
port of 555,908/65. of stone, that quantity being the remaining 
yjths of the entire weight, or 707,520 lbs. 

The dimensions which he assigns to his timbers (all supposed to 
be of oak) are as follow: 

The exterior ring, or arch-mould, consists of separate pieces of 
oak plank, bolted together so as to make it 12 inches broad, and 
6 inches thick. 

The main stretcher A A 12 inches square, and 

The straining piece h of same dimensions. 

The lower struts, 10 by 8 inches. 

The king post, 12 by 12. 

The upper struts, 10 by 6. 

The bridles, 20 by 8. 

M. Pitot assumes that a square inch of sound oak will carry 
8,640/65.; but this is known to be very far below the usual 
strength of good oak, and he probably means that this load may 
be laid upon it, with perfect security, for any length of time. 
But to make his computation certain and free from risk, and on a 
supposition that the timber may not be quite perfect, but may 
contain knots, shakes, and other imperfections that may affect its 
strength, he even makes a still further deduction, and only assumes 
7,200 lbs. as the measure of the absolute strength of each inch. 

The load to be supported by each rib, as before stated, is y^ths 
of 707,520 lbs. or 555,908 lbs. Now the two lower extremities of 
the arch mould being nearly perpendicular, and being prevented 
leaving that position by the framing on the one side and the arch 
stones on the other, will assist in supporting the load at the rate 
of 7200 lbs. for each square inch of surface. The dimension of 



600 OF CARPENTRY. 

this piece as given above, is 12x6, or 72 square inches; and 
72 m.x7200 lbs. gives 518,400 lbs. as the quantity of support 
afforded at each end by this piece. And in like manner the sus- 
taining force of each of the lower struts, presuming that they 
stand perpendicularly to the pressure, will be 576,000 lbs. The 
deduction for obliquity, will, however, not be material in the pro- 
cess about to be adopted, and leaving this for the present, the total 
sustaining power will be twice the power of the arch mould, or 
1,036,800 Ibs.f because it has two ends; and as there are 4 lower 
struts, we shall have to add 576,000X4=2,304,000 lbs. to this 
sum to obtain the total sustaining power, which will be found 
3,340,800 lbs. to support 555,908 /6.9., the entire load, provided it 
pressed perpendicularly upon the supports; but it does not do so; 
consequently, we shall have to carry the investigation further to 
determine the value of the oblique forces, and this may be done 
on the principles before explained, viz: by deducing those forces 
to a parallelogram with sides proportionate to the forces, and thus 
obtaining a resultant. 

1085. In order to compare the relative lengths of the sides of 
such parallelogram and its diagonal, it is necessary to make use 
of a scale of equal parts, by means of which we can set off the 
lengths of such sides in distances proportionate to the existing 
forces, and measure the results by the same divisions. Upon such 
a scale we may take divisions of any convenient size to express 
576,000, and must set this quantity off upon each of the lower 
struts to express their sustaining force, which we will suppose 
done by the dotted lines a, t a, s, and as the exterior strut is as- 
sisted by the arch mould to the extent of 518,400 lbs., we must 
set off a second quantity of this amount in continuation of the ex- 
terior right line as from t to e, which will make the entire length 
of one side of the parallelogram equal to a e, while its other side 
will be a, s] and now the parallelogram may be completed by 
drawing the lines s x and e x equal in length, and parallel to the 
lines opposite to them, and then drawing the diagonal a x, its 
length will express the conjoined supporting power of all the 
pieces, provided the pressure was exerted in the direction of the 
line a x. But this is not the case, because the stones are acted 
upon by gravitation, and the maximum of that force will be in a 
direction perpendicular to the horizon, and not in the oblique 
direction of a x. We must, therefore, let fall a perpendicular to 
the horizon 'a.s x y from the point x, so that it may pass by and 
cut a horizontal line a 6, upon or parallel to the line joining the 
two feet of the rib in the point c'; then take the distance a c' and 
set it off on that horizontal line at 6, so that a c'=c' b. From the 
point b draw a right line parallel to a x, and of similar length, 



CENTRING FOR BRIDGES. 601 

and it wiH cut the perpendicular below y in the plate. Join x b 
and draw a line a w parallel to it, by which a large parallelo- 
gram a X by will be produced, of which the line x c y \s a ver- 
tical diagonal, and the proportional length of this diagonal will 
express the strength of the rib; because one of its sides a x ex- 
presses the strength of support on one side; and that operation has 
to be repeated for the other, and that is done by drawing the line 
X b, which, of course, is the representative of the strength on that 
side; therefore the lines a x, x b, are the given sides of the paral- 
lelogram, and their sum expresses the supporting force they will 
exert in their oblique directions; and the diagonal x y carried 
down to their point of junction, reduces the sum of the two oblique 
pressures to a single perpendicular one or resultant, and the pro- 
portionate length of X y upon the scale, will express the amount 
of force that is in existence to support the load. This length 
upon the scale will be found equal to 2,850,000 lbs., and as the 
entire load, even without reducing it to the |Jths before mention- 
ed, is but 707,520 lbs.; we see that the dimensions of the timber 
as assigned by M. Pitot, are much too large; because the cen- 
tring has upwards of four times the strength which is necessary for 
bearing the load; 4 times 705,520 being but 2,822,080 lbs. It 
should, however, be observed, that in the above calculation of the 
weight of the load, the quantity of stone is alone taken into ac- 
count, without any allowance being made for the weight of the 
upper truss of the centring or its lagging, which in an arch of 60 
feet span will be considerable; besides which, an allowance should 
be made for workmen, tools, and materials, and for concussions 
that may arise in fixing the work, all of which are borne upon the 
centring, and require it to be stronger than would otherwise be 
necessary. 

1086. As the foregoing investigation applies only to the power 
of the lower struts, to support the upper part of the centring, 
together with the work that may be placed upon it, a like ex- 
amination must be made of the upper truss of the rib, which, from 
its similarity to the general form of roofs, may be estimated by 
the principles already explained as applying to them, with this 
difference only, that the strength of the timber composing the arch 
mould must also be taken into account, for this number does not 
exist in roofs. The method of proceeding is as follows: The force 
of each strut is 432,000, and that of the curve is 518,400; there- 
fore draw two lines from the top of the centre of the king post, 
the first m v parallel to the lower strut c, and make its length 
equal to 432,000, and the second upon the upper strut, and make 
its length m s equal to 432,000+518,000 or 950,000, complete the 
parallelogram m s r v, and draw a horizontal line r k from the 
76 



602 OF CARPENTHY. 

lowest point of that parallelogram, cutting the vertical line m q 
in k, and make k q equal to k m. It is plain from what was done 
for the lower part, that m q will be the measure of the load that 
can be carried by the upper part; and this will be found equal to 
1,160,000. This is a strength greatly superior to what is wanted, 
but not in so large a proportion as the under part, although the 
chief part of the load lies on the upper part. The reason of the 
great difference in the strength of the two parts, arises from the 
greater obliquity of the upper struts, which shortens the diagonal 
m q o( the parallelogram of forces, and shows that M. Pitot was 
in error in making the scantling of the upper struts more slender 
than the lower, when in fact they should be stouter. 

The strain on the stretcher A A is not calculated, but it is 
measured hy r k when m- q is the load actually lying on the upper 
part. Less than the sixth part of the cohesion of the stretcher is 
more than sufficient for the horizontal thrust; and there is no dif- 
ficulty in making the foot joints of the struts abundantly strong for 
the purpose. The above computation, it will be seen, does not 
give the strains exerted upon each individual piece; but the load 
upon the whole, upon a supposition that each piece is subjected 
to a strain proportioned to its strength. The other calculation 
would be much more complicated, and is not necessary here. The 
directions above given, can of course be applied to centres differ- 
ently constructed. 

1087. When the principles of roof construction are not retained 
in the formation of centres, polygons, or opposite struts are gene- 
rally resorted to. Hupeau's centring for Orleans bridge, before 
described by Fig. 253, is a frame composed of polygons; but in 
this, the sides of the inner and outer polygon are nearly parallel 
to each other, and the ends of those sides all terminate, one over 
the other, in liaes that radiate nearly from the centre of the arch. 
Perronet, a very celebrated French Architect and Engineer, has 
preserved this mode of construction, and he built many of the 
finest bridges of France upon centres of this kind; but instead of 
making the adjacent polygons nearly parallel, he arranged his 
timbers in such manner, that the angles of the one polygon were 
brought into contact with the middles of the sides of the adjacent 
one, and he used at least three of such polygons. This disposition 
of parts, will be rendered plain by reference to Fig. 257, which is 
an exemplification of this mode of construction, but not a copy of 
any particular centre that has been used. In nearly all the ex- 
amples of Perronet's centres, the inner and outer polygons are 
brought very nearly or quite into contact with each other at the 
springings, or opposite ends, which may afford facility in support- 
ing the centring while in use, but cannot add to its strength. In 



CENTRING FOR BRIDGES, 603 

our figure the sides of the outer polygon are formed of the pieces 
ab,b c, c d; and the next within by other pieces h e, ef,fg, and 
g I, so that the angles efg of the second polygon, come in contact 
with the middles of the sides of the outer one, which of course 
carries the arch mould blocked up as before described, hi kl, 
Is a third polygon within the others, but parallel to the outer one, 
and its angles likewise come into contact with the middles of the 
sides of the intermediate one. By this construction the angles of 
the alternate trusses lie in lines pointing to the centre of the 
curve. King posts are therefore placed in this direction between 
the adjoining beams of the trusses as at ef and g. These king 
posts consist of two beams, one on each side of the truss, and they 
embrace the truss beams between them, meeting in the middle of 
their thickness. The abutting beams are morticed half into each 
half of the post, and when the king post intersects the middle of 
a truss beam, such beam passes through it by their being let into 
each other, after which they are bolted or keyed through with 
iron. In this manner the whole is united, and it is expected that 
when the load is laid on the uppermost truss, it will all butt to- 
gether, forcing down the king post, and therefore pressing them 
on the beams of all the inferior trusses, causing them also to butt 
on each other and bear a share of the load. 

1088. The bridge of Cravaut was built by Perronet on centring 
of this construction. The arches were elliptical, of 60 feet span 
and 20 feet rise. The arch stones 4 feet thick, and weighed 
176 lbs. to the cube foot. The truss beams were 15 to 18 feet 
long each, and their section 9 by 8 inches. The king posts about 
7 iaet long, and each half in section 9 by 8 inches. The whole 
was of oak timber, and 5 trusses were used for each arch, placed 
5 J feet asunder. The weight of an entire arch was 558 tons, or 
about 112 tons upon each truss; and of this, nearly 90 tons actu- 
ally pressed upon the truss. When this centring is examined by 
the method before pointed out (1085-6) it is found competent to sus- 
tain a much greater load than was placed upon it. 

1089. The bridge of Neuilly, near Paris, is another of Perronet's 
works, in which the same kind of centring was used; but as the 
arches were larger, having a span of 120 with a rise of 30 (e^t, 
four polygons of truss beams were used. The stone arch was five 
feet thick, and the ribs were set six {eG.i apart. The strut or truss 
beams in this centre were 17 by 14 inches scantling; the king 
posts 15 by 9 inches in each half, and the ribs were tied together 
by five horizontal divided beams, running from one rib to the 
other, 15 by 9 inches in each half, and eight entire beams of 9 
inches square. The absolute weight of stone (without deduction 
for position) is 35 tons to each rib. The bridge was built upon 



604 OP CARPENTRY. 

this centring, which was strong enough to bear its load, but very- 
deficient in stiffness, for it sunlc upwards of 13 inches before the 
key stones were laid; and during the progress of the work, the 
crown rose and sunk by Various steps, as the loading was extended 
along it. This want of stiffness arose from the use of four polygons 
placed so near to each other that they became nearly parallel, or 
presented very obtuse angles to each other and to the king posts. 
The centre would therefore have been much stronger had it con- 
sisted of fewer pieces, forming more acute angles. 

1090. We shall conclude our observations on this branch of 
carpentry, with an account of the construction designed and used 
by Mr. Mylne, in building Blackfriars bridge, London, as this has 
been generally considered as the best and most efficient centring 
of any. It takes about one-third more timber than Perronet's 
plan; but it is beyond all comparison stronger. The leading prin- 
ciple of this centre is, that every part of the arch shall he supported 
by a simple truss of two legs, resting one on each pier. This principle 
is illustrated by Fig. 258, in which a and 6 are the two soles of 
the semicircular arch mould a d c eh. The truss in every place 
consists of two straight beams, one end of which rest upon the 
soles, while the two upper ends meet at the arch mould. Thus, 
a c 6 is one truss which supports the crown of the arch at c, 
a db Is another truss crossing the first, and giving support to the 
point d. a e h Is EL third truss to support the point e, and these 
trusses may be multiplied to any required extent. The only de- 
viation from this plan that was made by Mr. Mylne in building 
the bridge was, that instead of causing all his struts to spring from 
nearly the same place, or from a small sole, (as done by Perronet 
in most of his centres,) he adopted an extended sole reaching from 
h to g, in Fig. 259, which is an elevation of this centre, as actu- 
ally executed and fixed; and by this means Mr. Mylne was enabled 
to throw the most serious and detrimental pressure of the load, 
(which is the crown or upper part of the arch before the key 
stone is set,) upon the very foundations or lowest parts of the 
piers; thus preventing the possibility of their being forced laterally 
out of their places, which is one of the worst accidents that can 
befall a bridge while building. The other variation that he made 
was that of introducing stretching beams, which he called apron 
pieces, between the upper ends of the beams, instead of letting 
them abut against each other. These apron pieces served a most 
important purpose, for they gave better abutments to the braces 
than could have been otherwise obtained, at the same time that 
they rendered their meeting angle much more acute than it other- 
wise would have been, by which the strength of the truss ^as 
improved; and as these pieces were applied directly under, and 



CENTRING FOR BRIDGES. 605 

were fitted and bolted to the curved arch mould, they made 
it much stiffer and stronger than it could otherwise have been 
made. 

1091. The central or largest arch of Blackfriars Bridge was 
100 feet span, and its arches are nearly semicircles, as they rise 
43 feet above their springing. The timbers used as struts were 12 
inches square, and as their length, in many places, was such as 
precluded the possibility of procuring them in single pieces, they 
were joined and made to abut on each other, such joints being se- 
cured by being grasped and held together by the double king 
posts g h, which were notched to fit the intersecting pieces, and 
held together by iron bolts. The frequent intersections that occur 
in this centring produced the necessity of letting many of the 
beams into each other, which must have weakened them consi- 
derably, and endangered their breaking by cross strains, if it were 
possible for the frame to change its shape; but the great breadth 
that was given to the trusses prevented such change, and the fact 
was, that no sinking or twisting whatever was observed during the 
progress of the mason's work, although the arch stones were more 
than six feet thick. Three points in a straight line were marked 
on the centres for this observation, and they were watched each 
day. The whole sinking of the crown, before setting the key 
stone, did not amount to an inch. 

1092. One peculiarity in this centre is in its base and the mode 
of supporting it, and lowering it afterwards for striking. Mr. 
Mylne used the precaution of constructing very wide coffer dams 
for his piers, so that they were nearly twice as broad at their 
commencing bases as they were where they appeared above 
water, and after carrying up these bases with perpendicular sides 
until they became level with the bottom of the river, they then 
diminished by regular oflfsets upon every course, so as to produce 
an approximation to an inverted arch, as will be seen in Fig. 259. 
This gave him an excellent opportunity of obtaining abutments 
for the lower ends of a set of five struts c c d, upon which the 
sloping platform a was formed; and this carried the seats, or bed 
pieces, of stout oak, one of which was placed under each end of 
each rib of the centre. The upper surfaces of these seats were 
cut into a series of inclined planes, like a zigzag scarfing, and the 
under sides of the soles, or end timbers of the ribs, were also cut 
into a similar form, as shown between/ and e, in the figure, and 
each face of the scarf was covered with a thick and smooth plate 
of copper. Between these two pieces was placed the striking 
wedge efi (made black in the figure,) and this consisted of a se- 
ries of wedges, one beyond the other, but all in one piece, formed 
of a large beam of hard oak, hooped with iron at the projecting 



•ie. 



606 OP CARPENTRY. 

end e, to prevent its splitting. The fornn of the wedges cut on 
this piece corresponded exactly with the inclined planes formed 
in the seat and sole. The striking wedges were so placed as to 
keep the seat and sole at the greatest possible distance from each 
other; but on driving in the end e, they would be permitted to 
approach, and the whole rib would thereby be slowly and gently 
drawn from its contact with the under side of the arch, without 
at any time losing any of the power by which it was supported, 
which is a most desirable object in the first striking of the cen- 
tring of a large arch. A solid block of wood was introduced be- 
hind the end of the wedge at /, to prevent the possibility of its 
sliding inwards by the pressure of the arch. When the wedges 
had to be driven, after the completion of the arch, these blocks 
were removed, and the driving was accomplished by a heavy 
beam of oak capped with iron, and suspended by chains reaching 
from the lower beams of the rib to its central part, so that it 
would be used like the battering ram of the ancients. A few 
moderate blows with this implement produced the desired effect, 
and the wedge was driven, and the rib lowered in a few minutes. 
The wedges under all the ribs must be driven simultaneously, be- 
cause if one rib had remained up, while the others were depress- 
ed, this would either cripple the arch, or break the remaining 
rib. It was suspected that the small space through which these 
wedges permitted the centring to descend would not be sufficient 
to allow for the settlement of the masonry; and, consequently, 
that the centres would not be released from the work; but Mr. 
Mylne had no such fear, and remained perfectly confident not 
only of the perfection of his centring, but of the workmanship of 
the arches also; and in this he was fully borne out, for none of his 
arches exceeded 1:^ inch in their settlement, while all those of 
Perronet, built upon his polygonal centres, sunk from 6 inches to 
23j inches, which last settlement occurred in the bridge of 
Neuilly. 

1093. In building Waterloo Bridge, London, (between 1811 
and 1817,) Mr. Rennie adopted the principles of the Blackfriars 
Bridge centring, with the exception of such trifling alterations as 
would adapt it to an elliptic arch of 120 feet span; and the same 
striking wedges and means of supporting the seats and soles were 
used, with complete success. 

In Westminster Bridge (built between 1739 and 1750) some- 
thing like the same principle was taken by M. Lubelye, but his 
centre is by no means so strong and perfect as that of Mylne's, 
because only a single pair of struts take their bearings on the 
soles and meet at the arch. The other struts, which rise from the 
soles, proceed in right lines until they meet the arch mould, and 



ON MEASURING CARPENTERS' WORK. 607 

from thence they transfer their pressure to the second strut, 
placed nearly at a right angle with the first, and terminating at 
its other end in some part of the arch-mould, where there is no- 
thing solid to resist it. The ribs consisted of two parallel poly- 
gons of timber, about 12 feet apart, presenting seven sides to the 
arch, and stiffened between with the braces before mentioned, 
which are kept in their places by eight double king posts bolted 
together. These ribs had soles of their full width, which rested 
on a bed platform for carrying the seats of each rib; and the seats 
and soles were kept apart by separate wedges, placed transverse- 
ly between them, but with long projecting points, so that when 
struck upon, they would release the wedges and permit the cen- 
tre to descend: The bed platforms were level, and were support- 
ed partly by perpendicular struts rising from the offsets of the 
pier, and partly by long pilej driven expressly for the purpose. 

1094. The exactitude and perfection of workmanship that is 
necessary in the formation of the centres for large arches, makes 
it absolutely necessary that a strong and firm stage, floor, or plat- 
form should be constructed expressly for building them upon. 
This platform is made truly level by being built upon short posts 
that are let into the ground, and it consists of girders and joists 
that are afterwards covered with two inch plank, and made fair 
and smooth on the top surface. Upon this platform every part of 
rib is accurately drawn with black oil paint, or is slightly cut into 
the wood of the actual size of the several pieces; consequently the 
platform must be rather larger than the rib to be constructed 
upon it, and it must be so strong as not to be twisted or thrown 
out of level by the heavy timbers that are brought upon it. The 
pieces may be worked on the ground n^ar the platform, but when 
finished are put together upon it, directly over the lines that have 
been drawn, in order to see that a perfect accordance between 
them takes place. Such a platform may seem expensive; but 
no expense should be spared to make a centring as perfect as 
possible, and when the ribs are finished and have been put to- 
gether, the main timbers of the platform may be converted into 
lagging for the centre, since in large arches the lagging is usually 
composed of v^'hole square timbers, ranged under the centre of each 
course of stones instead of planking. 

1095. In pursuance of the plan previously adopted, the subject 
of carpentry will be concluded by some observations on the mea- 
surement and valuation of carpenters' work. 

The measurement of carpenters' work is very simple, and de- 
pends upon the principles already laid down in several preceding 
places; but that of joiners' work, although more simple, inasmuch 
as it scarcely ever involves anything beyond lineal and superficial 



608 OF CARPEJTTRY. 

measure, becomes apparently intricate from the great variety of 
technical terms made use of in joinery to express the forms of 
things, or the articles made. Generally speaking, however, all 
doors, sashes, shutters, floors, stair steps, &c. with their architraves, 
surbases, jaumbs, soffits, and other articles made by the joiner, 
are measured by the surface they present superficially, and are 
charged at so much the square foot; the price being regulated by 
their intricacy and finish, which will occupy more or less time. If 
work is enriched with many mouldings, and a superficial price to 
include the whole cannot be agreed upon, it is a common practice 
to obtain a price, by measuring the ground-work as plain work, 
which is covered by well known prices, and then to add the extra 
mouldings and ornaments at so much per foot, running measure, 
according to their length. The price per foot super, of joiners' 
work is deduced from the quantity of that kind of work which a 
good and competent workman, with every convenience around him, 
ought to do in an hour, a day, or any stated portion of time; and 
in computing the value of such work the labour only is taken into 
account, without the value of the wood, or 5/z/^ consumed. This 
is called the price for labour only. But when the joiner provides 
stuff, its value must be added to that of the workmanship, and it 
is then called the price for labour and materials. 

1096. Carpenters' work is done under three distinct contracts, 
called labour and all materials; labour and nails; and labour only. 
The first is when the workman provides the timber for his em- 
ployer, and does all the necessary work upon it, at the same time 
providing the necessary materials such as glue, nails, screws, &c. 
for putting the work together. But locks, bolts, hinges, and other 
articles of ironmongery are never included, but constitute a sepa- 
rate charge, according to their number and value. The second 
head, labour and nails, implies that the employer provides all tim- 
ber and other materials, except nails, and that the workman puts 
the work together and fixes it, he finding all such nails, spikes, or 
trenails as are necessary, but nothing else; and the third head is 
where every thing is provided by the employer, and the workman 
merely furnishes labour. 

1097. The first mode of working is generally resorted to for all 
small jobs, in which it would not be w^orth the employer's while 
to purchase his own materials, especially as he might procure too 
much or too little, and every carpenter usually keeps a small 
stock of such materials on hand. 

1098. The second mode, of finding labour and nails, is the one 
constantly resorted to in England for all building contracts; it has 
come into use from the very careless manner in which nails are 
treated by workmen, unless they have to pay for them. When 



ON MEASURING CARPENTERS' WORK. 609 

this is not the case, as many nails are frequently spilt among the 
shavings and swept away as would complete the job, while in 
labour and nail work, a spare nail is seldom seen upon the ground. 
In England nails are likewise an article of ready sale; and are 
therefore frequently purloined by labourers, unless they are taken 
good care of. 

1099. In the large cities of the United States, the two first plans 
are adopted as in England; but away from them, the mode of 
labour only, and the employer finding all materials is in constant 
use, notwithstanding it is the most wasteful and expensive process 
that can be used; for the employer is seldom as good a judge of 
the materials and their prices as the workman, nor does he know 
in what proportion they ought to be procured. He therefore 
often has a considerable stock left on hand when his work is com- 
pleted, or experiences a scarcity of some articles in its progress 
which compels him to substitute one size for another, or one kind 
of material for another, so as almost to preclude the possibility of 
perfection in his operations. 

1100. All carpenter's work, whether done by one or other of 
the above contracts, is measured and charged for by superficial 
measure, taken in what are called squares, that is, 100 superficial 
fefet, or else by the single foot. Thus all naked floors, roofs, or 
partitions (979) are computed in squares and y^ parts of a square, 
being superficial feet, and they are said to be worth a certain 
price per square, according to the distance apart of the joists, 
rafters, or studs, and whether they are morticed into, or simply 
notched down upon bridging joists, girders, &c. If a carpenter 
covers a naked partition with weather boarding, or a naked floor 
with boards or battens, still the measure and value is determined 
by the number of squares. A square of work is therefore worth 
a certain price for labour only; but if nails are also found, then 
the value of as many nails as ought to be used in a square of such 
work must be added. When the work is small and neat, it is 
taken in superficial feet instead of squares, while skirtings and 
many other things belonging more to joinery than carpentry, are 
measured and valued by lineal feet. It will thus be seen that the 
measurement of carpenter's work for labour only, or labour and 
nails, is very simple; but when all materials have been found, the 
above process must be gone through, and the price of the mate- 
rials must be added, which increases the complication of the pro- 
cess, because not only the general surface, but each individual 
piece of timber that occurs in the work has to be measured and 
set down in three dimensions, viz: length, breadth, and thickness, 
to determine its cubic measure. The kind of timber must also be 
specified in the measuring book, provided the timbers used are of 

77 



610 OF CARPENTRY. 

various kinds, with different prices per foot cube. The same ruling 
is used for the carpenter's measuring book as for the bricklayer's, 
(see 942,) and the columns are appropriated to the same purposes, 
viz: the first on left for coefficients, when pieces of the same size 
are often repeated, as in joists and rafters. The second column 
for the dimensions as taken; but these are always set down in 
three, instead of two lines or quantities, the breadth occupying 
the top line, the width the second, and the length the third; be- 
cause to cube timber the breadth and width are multiplied into 
each other, and their product into the length. The third column 
is therefore left blank for receiving the cubic quantities, when 
afterwards computed at home, and this quantity must of course 
be multiphed by the coefficient, when one exists. The fourth 
column is tilled up with the kind and quality of limber, as oak, 
pine, &c. and the form in which it exists in the work, as joists, lin- 
tels, rafters, &c. This dimension book not only requires to be cast 
up, but to be afterwards abstracted, (see 945,) in order that all 
the same quality of timber (or work if required) may be got to- 
gether, when the whole quantities can be stated in single sums 
with the appropriate value set against each. The table given at 
paragraph 570, will often prove very useful in reducing these cal- 
culations into value. 

1101. Piles used in foundations are valued at per piece, or by 
cubic measure; and, if their driving is contracted for, it is estimated 
by the foot run, according to their length, size, and the nature of 
the ground. Centring for arches is sometimes made and fixed by 
the square; but, in general, the Engineer considers this as work 
of too nice a nature to be trusted to contractors, and he prefers 
executing it as day-work by the best hands. Wall plates, lintels, 
and bond timber are measured by the cubic foot, under the 
denomination of fir or oak in bond. 

1 102. All timber used in foundations, naked floors, ceilings, &c. 
should be measured in presence of all parties concerned, as soon 
as fixed, because disputes frequently arise about the size and 
quality of timber after it is buried in the ground, or concealed by 
boarding or plastering, and these can only be arranged by un- 
doing part 'of the finished work, occasioning delay, expense, and 
inconvenience. 

1103. In measuring timber that is plained or wrought, the 
size of the piece before worked upon must be set down; also 
in pieces on which tenons or mitres have been cut, the length 
must be taken to the extreme end of the tenon or mitre, as these 
were as large as the rest of the stick before cut; and when the 
net quantity of timber found in any regular work is measured 
and set down, a twentieth part of the gross quantity is usually 



ON MEASURING carpenters' WORK. 611 

added, to allow for inevitable waste, on account of the ends of all 
planks, boards and sticks being split, shakey, and unfit for use; 
on which account they are cut off. which is also the case with the 
sides of boards, and many other pieces. This allowance would not, 
however, compensate for circular work, such as the ribs or arch- 
moulds of centres, and the curbs for sinking wells, for thes^, though 
curved, are cut out of straight wood, and as the curved pieces 
that come off are cross-grained and useless, so the actual size of 
the piece of timber, before converted, is always chargjed for, in- 
stead of the net quantity that occurs in the curved piece that is 
used. 

1104. Journeymen carpenters and joiners are always expected 
to provide and furnish their own tools, the use of which is included 
in the price of their wages; but the bench they work at, and a 
grindstone for sharpening such tools, are provided by the employer, 
together with any tools that may be necessary for particular and 
uncommon operations. 



CHAPTER XI. 



ON FOUNDATIONS AND THE USE AND CONSTRUCTION OF STONE AND 

BRICK ARCHES. 

Section T. — On Foundations. 

1105. Large arches of stone or bricks cannot be built without 
the assistance of centring, such as has been described at the close 
of the last section on carpentry. Such centres are, therefore, a 
necessary appendage to every arch: as, however, they are not 
permanent, but are taken away as soon as the arch is finished, 
and are constructed of timber by the rules of carpentry, they 
have been described under that head, as belonging more particu- 
larly to that branch of art, than to the arch itself. 

1106. No arch can be constructed until the two foundations 
that are to support it have been prepared, and the form and con- 
struction of these is subject to great variation. Thus an arch 
may rise or spring directly from the ground, in which case mere 



612 ON FOUNDATIONS. 

foundations will be necessary; and in such cases, they are called 
abutments. In bridges, and many other erections, the arches are 
elevated considerably above the level of the ground, and then the 
supports are called piers. In architectural constructions, arches 
are very frequently supported by colunans — the entablature, (in- 
cluding the architrave, the frieze, and the cornice,) intervening 
between the tops of the columns and the springinojor commence- 
ments of the arch; and this mode of construction has in some few 
instances been adopted in ornamental bridge building to save the 
heavy appearance of a pier of solid masonry. Macclesfield bridge 
of three arches, in the Regent's Park, London, designed by Mr. 
Morgan, is an elegant example of a bridge of this description. 
Before entering on the subject of arch construction, some atten- 
tion must be given to the formation of the abutments or piers that 
are to carry them, which affords an opportunity of speaking of 
foundations generally, and making those observations upon them 
which were referred to in the note appended to Art. 902. 

1107. The foundation of every wall or building ought to be 
depressed or sunk at least a foot or two below the general surface 
of the land, or much more if the building is large, in order to 
guard against the effects of frost, and to insure the soil from not 
being washed away by rains, or moved by other causes; and this 
depth should be increased if the erection is proposed to be made 
on an eminence. As a general rule, in making foundations for 
brick or stone walls, the upper vegetable mould, or soft covering 
soil of the land, should be cut through, and the excavation be car- 
ried down until the natural firm soil of the country is reached. 
Should the subsoil be rock or hard stone, no doubt need be enter- 
tained of the goodness of the foundation to bear its load; but that 
rock or stone ought to be under ground, because if it is exposed 
laterally to the action of the atmosphere or rains, it may moulder 
and decay with time. If no rock is met with, but the soil hap- 
pens to be clay, gravel, or even sand, it may in general be trusted, 
provided it is ground, or land that has not been dug up and moved; 
for these several soils at the depth of from two to four feet beneath 
the vegetable surface mould, will in general be found hard and 
compact enough to bear almost any load, particularly if the earth 
pressed upon has no opportunity of moving or escaping laterally. 
Sand is almost proverbially a bad foundation to build upon; but 
it is only so when it is not confined, as in an open beach, where 
it is liable to be washed away, or even drifted by the winds, so 
that the wall may become undermined^ But when sand is met 
with in the bottom of a foundation trench, in a tolerably dry 
state, and is to be covered on its upper surface with the intended 
erection, it may in general be trusted to as safely as soil of a more 



ON FOUNDATIONS. 613 

compact and fixed kind. If, Iiovvever, sand contains a snnall por- 
tion of loam or clay, and is in the vicinity of a spring, or is other- 
wise mixed with a considerable quantity of water, it will be semi- 
fluid, and will possess the property of fluids of giving way to any 
pressure exerted upon it by rising upwards or expanding laterally, 
when it is denominated quicksand, and of course cannot be trusted 
as a foundation; and when this occurs, the trench must be dug 
deeper, and as much of the wet sand as possible being taken out 
by a swinging scoop or other means, its place must be supplied by 
hard stones or rubble-work, or even by driving piles; and in such 
cases the Beton or concrete mortar before described (929) may be 
applied with advantage. 

1108. No made ground or embankment, that is, earth that has 
been shifted or moved to produce a level surface, should be trust- 
ed as a foundation for a heavy erection until it has had several 
years to settle and become hard and compact; for notwithstand- 
ing an embankment may have been regularly punned or rammed, 
yet it will always sink or settle to some extent. When, there- 
fore, a building is required upon such a bottom, the foundation 
trenches should be dug through the made soil to the untouched 
earth beneath it. This would often lead to a heavy expense both 
in excavation and in brickwork; therefore the walls may be sup- 
ported upon arches standing on piers, which alone go down to the 
solid earth. This expedient was resorted to in building the north- 
ern boundary wall of the yard of the new House of Correction in 
Cold Bath Fields, London, which extended over a large piece of 
hollow ground, which had for many years been made the recepta- 
cle for the rubbish of that part of the city, and consequently was 
all made or artificial ground to a depth of many feet. In this in- 
stance the arches sprung so low down that no part of them ap- 
peared above the level of the ground when finished, and the wall 
stood as firmly as if it had been built on solid ground. 

1109. When a foundation trench has been dug even in natural 
ground, it frequently happens that the entire length may rot be 
equally solid and hard. Should soft places occur without being 
very extensive, they may be arched over as above described, the 
arches taking their abutments upon such portions of wall as are 
built upon the solid ground. Whenever foundations appear doubt- 
ful, the solidity of the earth is tried by driving stakes into it, or 
by the use of an iron borer with a T shaped head, by which it is 
turned and forced downwards into the ground. Should its entrance 
be resisted, the ground may be deemed trustworthy; but should it 
pass easily, it will not be fit for building upon without some pre- 
paration and assistance. 

1110. All foundation trenches should be perfectly level at their 



614 ON FOUNDATIONS. 

bottoms, and need not be wider than what is merely necessary fop 
introducing and laying the stones or bricks in mortar. If, there- 
fore, a foundation has to be formed in the slope pf a hill, that 
foundation should not follow the slope of such hill, but should be 
cut in level steps, like a staircase, except that the level portions 
may extend considerable distances. 

1111. When the erection about to be constructed is not a wall 
of equal thickness and weight throughout, but consists of piers 
with window^s or openings between them, or of columns that are 
heavy, or have to carry large weights, the pressure on the founda- 
tion will not be equal, but will produce a greater strain imme- 
diately under such columns or piers than in other places. A foot- 
ing or foundation of equal strength w^ould, therefore, be subject to 
bend, break, or loose its right lined form. To resist such unequal 
pressure, inverted arches, or what are technically called Inverts, 
are resorted to. These are nothing more tlian the common arch, 
constructed of stone or brick, (but generally of the latter mate- 
rial,) but placed with the convex surface of the arch downwards, 
instead of in its usual position. Such arches, of course, require 
no centring for their construction, but the materials of which thev 
are formed are supported either in regular curved foundations cut 
to a mould-board or template, if the ground is stiff clay, or any 
soil that will hold its shape without crumbling, or falling down, or 
more frequently in concavities formed in a brick or stone founda- 
tion which is commenced in the usual right lined horizontal 
direction. Fig. 260, Pi. VIIL, shows such an arrangement as 
adopted round the Girard College, now building near Philadelphia, 
for supporting the immense massive columns of the colonnade that 
will surround that building. A regular level and straight founda- 
tion of brick-work is began at a a, and is carried up a certain 
heis;bt, when the inverted semicircles or segments h h are left in 
the wall, being accurately worked to their regular shape by 
mould-boards, or by sweeping strips, fixed to turn on the true 
centres of the required arches, when the openings are so large as 
to render a mould inconvenient. These concave openings are 
afterwards filled in with two, three, four or more concentric rows 
of arch brick-work h 6, all terminating in the upper horizontal 
line e c. These hollow arches are afterwards filled in w^ith hori- 
zontal courses of brick-work dd, so as to bring the top of the 
foundation wall to one uniform level c e, upon which the columns, 
piers, or other detached loads must be built, taking care to place 
each column or pier over the entire joint-springing of every two 
arches, by which means the load, that would otherwise bear only 
on the space directly under it, is distributed over the whole extent 
q[ the arch, the span of which must, of course, extend from the 



INVERTED ARCHES. 615 

centre of any one column or pier to the centre of the one adjacent 
to it. 

Inverted arches are also very useful in places where founda- 
tions may be liable to be undermined, disturbed, or carried away 
by a flow of water; and for this reason they are often adopted under 
the bottoms of canal locks, where, from the nature of the soil in 
which the lock is built, there may be a danger of its washing 
away. In such cases the inverted arch takes its springings from 
under the side walls of the lock, and forms the base or foundation 
upon which these walls are built; the inverted arch, of course, 
extending the full length as well as width of the lock. 

1112. The greatest danger to be apprehended in a foundation 
of natural soil which may appear good, is from its not being equal- 
ly hard and trustworthy in every part of its length. To obviate 
which, it is very custom.ary to lay down thick oak, or other planks, 
to build upon; but this is by no means a good practice, unless the 
foundation is so deep as to insure such timber being constantly 
under water (665). When this is not the case the timber will 
soon decay; and whenever this occurs the wall is left without 
support, or perhaps partially supported, from one part of the plat- 
form decaying more rapidly than another. In all cases, therefore, 
where such assistance is necessary it should be obtained from 
large flat stones of the slab or lamellar formation (463); and some 
of the varieties of slate and York paving are excellent for this 
purpose. Such stones should be of sufficient thickness to sustain the 
superincumbent weight without breaking, and the more effectually 
to guard against this accident, they should be very carefully bed- 
ded, or be so placed on the ground as to leave no hollovi^ places 
under them. This, in general, may be guarded against by digging 
the foundation trench wider than is necessary, making the bottom 
to fit or suit the under surface of the stone, (should it not be quite 
flat,) and then driving earth under the stone at its sides by a 
stone hammer, after it is placed. 

1113. The ground under a foundation is sometimes of so loose 
and open a nature that it may not prove solid, even if excavated 
to a very considerable distance, and when this is the case the 
driving oi^ piles may become necessary. Piles are usually made 
of whole round timber (548) cut to proper lengths, or of baulks, 
from which the rough bark and any projections have been hewn 
off, to fit them for passing more readily into the ground; and the 
descending end is pointed for the same object. Should the ground 
be hard or stoney, the end will require the assistance of a wrought 
iron point, which is formed with four spreading tails with holes 
through them for nailing them to the sides of the point of the pile; 
the upper end of the pile must likewise be encompassed by a strong 



616 ON FOUNDATIONS. 

wrought iron hoop, to prevent it from splitting in the driving. 
The points, or shoes, may be made of cast iron for soft, sandy, or 
clay soils, that being a cheaper material, and the point, or shoe, 
being lost for ever; but one hoop will serve for many piles, because 
it is only useful during the driving, and is afterwards taken off to 
serve for other piles. 

1114. Piles are used for a twofold object, one of which is to 
condense or harden loose ground, which they do on the principle 
of the wedge, by inducing lateral pressure; the other is to trans- 
fer the load to a deeper part of the soil than that which has been 
laid bare, when it is found that the ground increases in solidity as 
it descends, or that a solid stratum of soil exists under that which 
has been laid open. To produce the first effect the piles need not 
be more than from four to six feet in length, and their lower part 
should be squared and gradually tapered from the point to the 
head, so as to give them the shape of elongated pyramids; and if 
charred, before driving, they will not only enter the ground more 
easily but will be more durable. For the second object the piles 
must of course be long enough to reach the hard ground from 
which the support is proposed to be derived; and whenever piles 
are long they ought to have but little taper or diminution of size, 
or the difficulty of driving them will be much increased. Every 
pile should, however, have some taper, because that affords mate- 
rial assistance in enabling it to support its load. 

That timber should be selected for piles that is known by expe- 
rience to be least liable to decay under ground, and it should be 
straight grained and tolerably free from knots, otherwise it will 
be liable to break in driving. Considerable care is also necessary 
in shaping the points to have the angles on all sides equal with 
their common summit in the centre or axis of the tree; for if this 
is not attended to, the pile cannot be driven in a perpendicular 
straight forward direction. Small piles are driven by a three hand 
maul, but large ones require a pile driving engine. 

1115. The three hand maul is a very large mallet made of a 
block of hard wood hooped with iron; it has two handles, which 
radiate from its centre, and are so far apart that two men can 
work it, one holding each handle, and it has a third short handle 
opposite to these. A man stands at the short handle merely to 
assist those at the long ones in raising the maul from the pile when 
a blow has to be made, and it 'descends by its own weight, urged 
by the strength of the two men at the long handles, and has great 
power, but could not be used for long piles, which stand their full 
height out of the ground before they are driven. Pile engines 
vary in size and construction with the length and size of the piles 
to be driven, and consist of a contrivance for raising a heavy block 



ON PILING FOUNDATIONS. 617 

of wood, 01* cast iron, to a certain height, and then letting it fall 
suddenly on the top of the pile, so that it may perfornn the ofijce 
of a heavy hamnner. Small pile engines are called bell ringing 
engines, on account of the weight (called the monkey when it 
is about 3 cwt, or less) being raised by a single rope which, 
after ascending to a sufficient height, passes over a large pulley 
and descends on the opposite side, where it is divided into six or 
eight smaller ropes, to each of which a separate man applies his 
force to raise the weight, and then they all slack out their ropes 
simultaneously, so that the operation appears very like that of 
ringing large bells by ropes. As the rise and fall of the weight is 
limited in this machine to the extent that the men's arms can 
reach, and the weight must be light in order that it maybe raised 
without mechanical power, this machine is only applicable to 
driving such short piles as are generally used in inland places; 
but it has the advantage of working quickly and being easily 
moved from one place to another. 

1116. In bridge building and other wet foundations, where 
longer and thicker piles are required, a more powerful machine 
becomes necessary. Its construction is nearly the same, but a 
heavier weight (now called a ram) is used, and it is drawn to a 
greater height that its blow may be more effective. The ram 
usually weighs from 5 to 8 cwt.^ and it is held by a pair of spring 
nippers to which the elevating rope is fastened, while the eleva- 
tion is produced by one or two men turning the handles of a crab 
(4(59). As soon as the ram is raised to the full intended height, 
the handles of the nippers are pressed together by two inclined 
planes, fixed on the top of the machine, which cause the nippers 
to open and release the weight, which falls free from the incum- 
brance of the rope, which is instantly lowered for lifting the weight 
again. The iron weight of a pile engine is cast with two square 
transverse holes, into which pieces of hard wood are firmly keyed 
to attach the weight to the guide posts for governing the direc- 
tion of the fall. The ringing engine is generally made with only 
one post of four or five inches square, and at least one-third longer 
than the piles to be driven. Its lower end is firmly morticed into 
the middle of a strong timber sill, so as to give it the appearance 
of a large T square (33), with a square instead of a flat blade. 
The pieces of wood that are keyed into the weight have square 
holes in them for the upright piece to pass into, and a large pul- 
ley is fixed on the upper end of the upright post, over which the 
elevating rope passes; consequently the weight can only rise and 
fall by the side of this post. The use of the transverse sill is to 
afford a foundation for the engine, and to maintain the perpen- 
dicular position of the post in one direction. It is then retained in 
78 



618 ON FOUNDATIONS. 

that position by three stays or guy ropes, with blocks and falls 
attached to the ground; and having been properly adjusted and 
fixed in its place the weight is raised and fixed in its highest posi- 
tion, and the pile to be driven being set in its proper perpendicu- 
lar position close to the engine post, the two are slightly tied or 
lashed together, and continue so until a few blows have driven 
the pile deep enough into the ground to enable it to maintain its 
own erect position. 

The larger engine is of the same construction, except that as 
the ram is very heavy and the range of motion longer, one up- 
right pole might not be strong enough, and two are therefore used 
parallel to each other, and about five inches asunder; and the 
pieces of wood keyed into the ram now pass between them, and 
the weight is prevented escaping by iron pins driven through the 
projecting ends of these pieces. This construction also admits of 
diagonal braces being introduced, from near the ends of the sill to 
the outsides of the uprights, by which the machine is much 
strengthened. It is fixed by guy ropes like the smaller engine, 
and the uprights must be so much higher than the piles to be 
driven as to leave a fall of at least four feet on the head of the 
pile, for commencing the driving. 

When piles have to be driven in rivers for bridge building, the 
engine must be supported between two strong boats or barges, 
firmly moored or fixed in their proper places, until a sufficient 
number of piles have been driven to afford a more stable mode of 
fixing it. It frequently happens that a large part of the work has 
to be done in barges, and the guy ropes and other fixings must 
then be attached solely to the barges, because should the water 
be subject to rise and fall from tides, or other cause, the ropes 
would not remain equally strained when otherwise attached. 

1117. In the building of Westminster Bridge, London, a very 
complete machine for driving piles, invented by Mr. Vauloue, was 
used. It was built on a barge and worked by a horse who went 
round constantly in the same direction, and with the same speed 
during the rise and fall of the ram. It was a most complete and 
perfect machine, containing several curious mechanical principles, 
on which account it is described with a figure in almost every 
English book on mechanics. But being complicated and expen- 
sive, its construction has not been repeated, except in models to 
explain its principles. As a great number of pile engines are fre- 
quently at work at once when a bridge or large construction is 
going on, and as they require to be constantly shifted from place 
to place, as the work proceeds, or even to be altered in adjust- 
ment of position while a single pile is driving, in case of its not 
going straight, these machines require to be cheap, simple, as 



ON PILING FOUNDATIONS. 619 

light and portable as possible, easily fixed and not readily put ont 
of order. Now, none of these qualities belong to Mr. Vauloue's 
engine, while they all appertain to such as have been described; 
and the surest proof of their being the best machines is, that they 
alone have been employed in the numerous large bridges and public 
works that have been executed in London, Liverpool, and other 
large cities of England within the last forty years. The only dif- 
ference that has been adopted has been that the ram has occa- 
sionally been raised by horse instead of human power, and the 
onlv alteration necessary in this case is that a horse mill or frame 
work, like that shown at Fig. 118, Pi. IV. must be provided, the 
drum, or cylinder, upon which the rope winds, being placed upon 
the central upright spindle b above the arm i, and that this drum 
should be loose or capable of revolving upon that spindle, but with 
a lever catch to lay hold of the arm with which the drum should 
be fixed or engaged, while the weight is rising, but by means of 
which it may be disengaged for the rope to run back for re- 
engaging the weight, without the slow and troublesome process of 
turning the direction of the horse, who may thus stand still until 
the weight is prepared for rising. 

1118. As the pile descends into the ground, it ought, and gene- 
rally will meet with increasing resistance: and this is met by the 
weight (which is always raised to the same height) having an in- 
creasing distance to fall through, as the pile recedes before it. A 
pile will frequently descend several inches with each of the first 
blows, but its rate of motion (which is ascertained by making 
chalk lines on the pile engine even with the top of the pile) will 
gradually decrease, and a pile is not considered as well driven 
and perfectly trustworthy, until it stops or refuses to go further, 
or at any rate makes an almost insensible progress. Thus, if a 
pile is not found to move a tenth of an inch after eight or ten suc- 
cessive blows of a heavy ram, it would only be throwing away 
time and money, besides, perhaps, splitting the pile if the opera- 
tion should continue; and, of course, though such pile may not 
have been driven half its length, the driving operation would 
cease, and the pile may be sawed off to its proper level. But, on 
the contrary, if the pile goes fully down to its top, and has de- 
scended several inches at each of the last blows, then it would not 
be safe to build upon it, but it must be left and other long piles 
must be driven round it, at from twelve to eighteen inches from 
its outside. These may have the effect of fixing it in the ground, 
which is ascertained by shifting the pile engine over it again, and 
giving it a few more blows. Should it still drive, then other inter- 
mediate piles must be introduced so as nearly to fill up the space 
between the first and se :ond sets; but, in general, piles seldom 



620 ON FOUNDATIONS. 

want such close approximation and should be kept at least their 
own dianaeter apart, not only to provide room for intermediate 
piles, but because when they are driven too closely together, the 
driving one pile will occasionally force those previously driven 
partly out of the ground, or at any rate will force up some of the 
intermediate soil, which is detrimental by loosening the ground. 

1119. All piles should be placed in right lined rows, and when 
fully driven their tops are sawed otf to a true level plane, because 
a timber sill or sleeper of sound die square timber, or thick plank, 
has to be placed upon each parallel row of piles, and is then 
spiked or trenailed down (992) to the top of each pile. The space 
between these sleepers should then be filled up with rubble-work, 
brick rubbish, or stones screened out of coarse gravel or other hard 
material, which should be well rammed into its place, or if the 
ground is springy may be grouted with mortar, mortar and cement, 
or wholly with cement, according to the nature of the soil, and 
the erection to be placed upon it, until the whole is brought to 
an even surface. Other pieces of timber are then laid at right 
angles across the sleepers, one over each transverse row of piles, 
and if these are distinct, one intermediate piece between each.. 
This forms what the French calls a grillage, or grating, and trans- 
fers the load evenly over all the piles driven. These pieces are, 
in like manner, filled in between them, so as to produce a level 
surface for buiidlng upon. That surface is sometimes covered all 
over with thick plank, to render it more smooth and even, but 
this is merely multiplying the layers of timber without an equiva- 
lent advantage, and should a more uniform surface be required, 
it will be better to obtain it by putting the cross timbers closer 
together. Sometimes the sleepers and cross pieces are halved on 
to each other to produce a level surface in the first instance. But 
this is a bad practice. It is, in fact, buying large and expensive 
timber, and then by cutting it half or partly through, diminishing 
its strength and laying open its heart or centre to the immediate 
action of humidity and the causticity of the lime. For the same 
reason I do not approve trenailing the cross pieces, or producing 
more holes or weakness than is absolutely necessary; because if 
the platform is laid truly level, no piece will have a tendency to 
move from its first position, particularly when loaded with brick- 
work or masonry. But should the platform be necessarily sloping, 
as is sometimes the case in the abutments of bridges, then there 
may be reason for notching the pieces into each other to prevent 
their sliding, but this notching should in no case proceed to half 
the thickness for the mere sake of obtaining an even surface. 

1120. While on the subject of piles, it may be stated that they 
are not only used to procure solid foundations, but occasionally as 



ON PILING FOUNDATIONS. 62^^ 

accessories to that end, by keeping back water or quicksand, and 
then they are called sheeting piles. Sheeting piles instead of being 
made of whole timber, are formed of thick piank, shot or jointed 
on the two edges, so that they may come closely together and 
form a water-tight, or nearly water-tight, joint. The more 
effectually to insure this, and the parallel position of the planks, 
their edges are frequently grooved and tongued (1015) into each 
other. They are driven by the same machine as other piles, but 
generally by the small or ringing engine, and to insure the con- 
tiguous edges keeping in close contact with each other, while 
driving, the angles of their points are all cut on one side only of 
(he pile, as shown at Fig. 261. 

1121. When foundations have to be sunk very deep, by which 
they get into the springs found in most land, or have to be made 
in wet places, it frequently happens that the water rises so rapid- 
ly, or that the sand and water, mixed together, are so fluid that 
they impede the progress of the workmen, so that draining by 
pumps or other means become necessary; and then it is that 
sheeting piles must be used to keep up earth, or to keep back 
sand and water. When any extent of such piles are necessary, 
guides for driving them, and afterwards retaining them in their 
proper positions, must be used. These guides are pieces of square 
timber placed horizontally parallel to each other, and as low as 
possible in the work. They are kept asunder by a short pile 
driven at each of their ends, to which they are spiked, or screw 
bolted. Their distance asunder must be about one quarter of an 
inch greater than the thickness of the sheeting piles about to be 
used, and which are formed of planks from two to five or six 
inches thick, according to the height and weight or quantity of 
water sand or loose earth they may have to sustain. The use of 
these guides is to direct and hold the piles in their proper places 
while driving, and to support them afterwards. The piles are^ 
therefore, introduced between the two guides, and if longer high, 
a single guide rail, placed three or four feet over the lowest one 
that is on the outside of the expected resistance, will be necessary 
for the piles to lean against. When the resistance is great both 
the upper and lower guides should be of strong whole timbers; the 
bottom one may be stiffened by short piles driven close behind it 
at short intervals, and the upper one may be strengthened by 
diagonal struts or braces. While the sheet of piles is fixing there 
will be no danger of irruption, because the water and sand will 
flow out, or rise to a common level on both sides; but when com- 
pleted and the water, sand, or mud is withdrawn from the exca- 
vation in which the work is to proceed, these materials may ac- 
cumulate and rise on the opposite side of the sheet, and break it 



622 FOUNDATIONS IN WATER. 

down or undermine its foundation, or may get round the sides un- 
less the work is well executed and stayed or braced, so as to pre- 
vent its changing its right lined position in consequence of lateral 
pressure. The sides of the piles must be well planed and fitted 
so as to make water-tight joints, and by cutting the points of the 
piles into the form shown at Fig. 261, the piles are forced into 
close contact with each other while driving, an elfect that is 
further assisted and promoted by binding the upper part of each 
pile, as it goes down, by a rope or light chain to the piles pre- 
viously driven, as at e e, in the figure. When the water to be 
arrested is very clean and clear, the joints of sheeting piles some- 
times require to be caulked with oakum, like the seams of a ship; 
but, in general, the clay and mud of the water settling in the 
joints, or smearing them over on the back side with wet clay will 
render them water-tight. The flow of water being thus conquer- 
ed the excavation to be used for the building must be cleared of 
water by pumping or other means, and this is frequently a very 
expensive operation, as powerful pumps are often necessary, some- 
times requiring the aid of a steam engine to work them; and 
when once pumping begins it should never cease by day or by 
night, for in a short cessation the water will gain or rise perhaps 
to its original level, and then all the previous labour is thrown 
away. It is not the mere water contained in the foundation pit 
that has to be drawn out, but in sandy soils all the water that 
the earth contains in a great distance around will percolate into a 
deep foundation, and the water in this way has laid dry every 
pump and well within a radius of about a mile from the place where 
the pumping was going on. 

1122. When difficult foundations of this kind occur, (and they 
are not uncommon in building the locks for navigable canals,) of 
course the whole foundation cannot be laid open at once, and the 
Engineer must be satisfied with clearing a small part at a time, 
and getting in a small portion of the work, which, if of brick or 
stone must, of course, be laid in hydraulic cement, or if of timber, 
not secured by piles or otherwise, must be loaded with stones or 
earth to prevent its floating. Indeed it is often a safe precaution 
to load even brick or stone-work, after it is laid in such situations, 
with a quantity of the soil dug out of the adjoining part of the 
foundation, merely to give it additional weight, and prevent its 
being washed away or disturbed, although that earth will have 
to be moved again before the work can proceed. The great diffi- 
culty in these cases is to get the platform or grillage, or the few 
first courses of the foundation laid, for when that is done, and a 
good hard and level bottom is obtained, the rest of the work is 
comparatively easy. Of course in these, as indeed in every other 



OP COFFER-DAMS. 623 

kind of foundation, the largest and most massive stones, with the 
flattest surfaces, should be laid, in order that they may cover and 
distribute the weight that is afterwards to come upon them over 
as large a space as possible. 

1123. When the foundation is wholly in water of considerable 
depth, as in building the piers of bridges, two distinct methods of 
proceeding must be adopted, depending on the nature of the bot- 
tom or foundation. Should the bottom be any thing but rock, 
coffer-dams are constructed, and the work will be comparatively 
easy; but, if the bottom is of rock, or of such hard materials as 
will make it impossible to drive piles into it, the difficulty is much 
increased, or the work may even be rendered impossible. A cof- 
fer-dam is a water-tight box, or casing, formed by driving piles of 
such length into the river, that while their lower ends may take 
good and firm hold of the ground, their tops may remain at least 
a foot or eighteen inches above the greatest height to which the 
water can possibly rise by tides, freshets, or other causes. Coffer- 
dams are necessary not only for the central pier, but for the ends 
or land abutments. For the former they are usually rectangular, 
and so placed that their sides may be parallel to those of the pier 
intended to be built; but for the land abutments they are usually 
semicircular, or half a polygon, and open on the land side, so that 
they can be walked or carted into, which affords facility for de- 
livering the materials; but of course the piling and damming must 
proceed a sufficient distance inland to prevent the possibility of 
the water ever rising so as to flow over them. 

The reason for making abutment dams half polygons, is for the 
sake of having straight string pieces and rows of sheeting piles, 
as will be presently described. With the exception of difference 
of form, all these dams are alike; consequently an account of the 
manner of forming one in a river will suffice for all. 

1124. The first step is of course to sound the river for its depth, 
and to bore into its bottom with an auger to determine the soil to 
be expected; for by this alone can the length of piles that will 
be necessary be determined. This known, drawings to scale must 
he made of a plan and elevation of the proposed pier, with the 
dam surrounding it. The pier must be shown of the size it is to 
have above water, together with the footings or offsets that are 
below, and out of sight. This is next surrounded by the inside of 
the dam, which ought to be placed at least four or five feet from 
the work, to allow room for the workmen to pass with materials. 
The thickness of the dam is next set out by lines drawn parallel 
to those that indicate its inside, and this must vary with the depth 
of water and other circumstances; but ought in no case to be less 
than six feet, including the timber; and if the river is wide, and 



624 FOUNDATIONS IN WATEK^ 

good puddling material can be readily obtained, it tvfll be better 
to nnake it ten feet thick, because this part of the dann, when 
finished, is the only one that can be used for landing and storing 
stones, mortar, and other materials. Should the depth of water 
5imount to more than ten (eetf it will be advisable to give it a 
greater thickness, amounting to twelve or fifteen feet Having 
thus set out the exterior dimensions of the dam in plan, the num- 
ber of piles to be employed can be determined; for one must be 
placed at each angle or corner, and the intervening space between 
these must be divided into such equal distances as will come nearest 
to four or five feet each; at each of v^7hich points, a long pile has 
to be driven, so as to inclose the space with a rectangle of four 
sides or rows of piles, about four feet asunder. These first piles 
should be very strong, made of squared timber, (the size depend* 
ing on their length,) and so long, that after driving from six to ten 
feet in the bottom of the river, their tops may be above the great- 
est possible elevation of the water. While this large or exterior 
rectangle of piles are driving, the smaller internal one that is to 
form the inside of the dam may also be going oil, observing that 
most of the inner piles should be at the same distance asunder as 
the outer ones, and be placed exactly opposite to them, so that a 
line strained over the centre of two opposite exterior piles, may 
also pass over the centres of two opposite interior ones. The 
string beams are next fixed; and these are whole pieces of square 
timber notched and screw bolted to each pile very near their 
tops, and surrounding each rectangle in a horizontal direction; 
and similar pieces are placed opposite to them in the inside of the 
piles, and of course, can be fixed by the same bolts running through 
both pieces and through the piles. The inside strings are often 
made of half timber, or a stick sawed through the middle, their 
chief use being to guide the sheeting piles in driving, and for them 
to rest upon when finished; but those on the outside should be 
very strong, as they not only bind all the piles together, but are 
intended for a protection against ice, logs, or any thing that may 
float down the strea'm; and should it be subject to these, or be 
navigable, it will be advisable to drive other strong piles, and 
string them together exterior to the outer row, to act as fenders 
or defenders, for preventing vessels or other objects striking 
against the dam. The rectangles of piles with their uniting strings 
constitutes the frame of the dam on which its strength chiefly de- 
pends; and when that is finished, the driving of the sheeting piles 
commences. These piles, for coffer-dam work, are never less than 
four inches thick, and when the depth is great, should be six 
inches. They are driven in close contact with each other in the 
inside of the string pieces of the outer rectangle, and the outside 



OF C0FFER-DA31S. 625 

of the strings of the inner one, so as to form two parallel cases or 
walls of sheeting piles, the bottonns of which must proceed at least 
six or eight feet into the bottom of the river, while their tops may 
be even with that of the main frame. If these piles have been 
well driven, and are close and water-tight, or nearly so, as they 
ought to be, pumping may be applied between these two walls to 
ascertain if the water within can be lowered or not. Whether it 
can or not, the puddling must now begin by filling up the space 
left between the two cases with good puddling earth, which, if 
the water can be sufficiently withdrawn by the pumps, may be 
worked, trampled, and treated as in a common puddle gutter 
(391). If, however, the water cannot be withdrawn, the puddling 
materials must be worked and prepared in a boat or barge on the 
outside of the dam, and thrown by shovels, or raised by buckets, 
and discharged into the space, in which, being heavier than 
water, they will subside — and they must be worked and pressed 
into a compact state by poles and rammers, worked by men from 
a scaffold made across the string pieces. In this way the space 
between the two rows of piles is filled up to the top, and covered 
with gravel, hard soil, or rough flooring, for walking upon, work- 
ing and landing stones, timber, or whatever may be required for 
the progress of the work. A gib or crane is frequently erected on 
the top of each coffer-dam, for the purpose of hoisting stones and 
heavy articles; and as this swings or turns on pivots, it atJbrds an 
easy means of landing such articles on the top of the dam, or 
lowering them at once into their proper places. It is also a com- 
mon practice to construct a strong but temporary timber bridge, 
from the shore to the several coffer dams as they are finished, 
which bridge carries a rail-road, and is wide enough for a horse 
to work upon it. This affords a convenient means of transporting 
the building materials and tools from the shore lo the work, as 
well as for the workmen to pass to and fro. 

1125. The dam may now be considered as water-tight as it can 
be made in the first instance; and the pumps may, therefore, be 
fixed upon it, for drawing off' the water within it, and discharging 
it on the outside. The pumps generally used are copper hand- 
pumps, placed two together, with a beam or lever over them, so 
disposed that as the piston of one pump rises the other falls. The 
lever has cross handles to it, so that several men may apply their 
strength at once at each end; and as the perpendicular lift is 
generally small, the pumps may be made of large diameter, such 
as twelve or fourteen inches. If the water makes rapidly in the 
dam, it will be cheaper to work the pumps by a small steam 
engine, which is generally placed on the shore, and its power is 
carried to the pumps by a swinging rod, generally called a flat 
79 



626 FOUNDATIONS IN WATER. 

rod shaft, which may be of wood, and is supported upon the tem- 
porary bridge. Should the dam be well constructed upon clay or any 
ground that is nearly impervious to water, the pumps will draw 
all the vvater from the inside of the dam and leave the natural 
soil or bottom within it exposed for digging or beginning the 
foundation with the same facility as if the work was doing on dry 
land. 

1126. When the coffer-dam is emptied of its water, it will be 
subject to the pressure of the outside water, which will be very 
considerable when the river is deep; consequently there will be 
danger of its collapsing, by its straight sides bending inwards. To 
resist this accident, stretching beams of whole timbers are laid 
transversely across the dam, and are halved down on to the string 
pieces, and bolted to them and the piles, so as to connect them 
together, and also to connect the two opposite sides of the dam. 
And as the water is got down, additional string pieces of strong 
timber should be introduced horizontally at every three feet from 
the top. These may be spiked on to the inner sheeting piles to re- 
tain them in their places, and then additional struts, or stretching 
beams, may be introduced across the dam, from one side to the 
other, and be tightly wedged and nailed between the strings, so 
as to effectually prevent the sides of the dam from bulging in- 
wards. It may seem that these cross pieces will be in the way of 
the pier as it is building, but this is of no consequence, for the 
building can go on until it reaches the first range of such cross 
pieces, and that done, short struts or stretchers are wedged in 
from the strings to the solid stone- work some inches below its top, 
after which the long stretchers may be cut away to make room 
for the work to be brought up until it reaches the next tier of 
stretchers, which are replaced, and moved as before. 

1127. The foundation in the bottom of a coffer dam is formed 
just as if it was in land. The loose mud and soil at the bottom of 
the dam is dug out and drawn to the top in boxes or tubs by a 
rope and windlass, as in digging wells, and it will be advantageous 
to the dam to discharge it into the water close to it, which gives 
the piling an additional footing of earth; but when this may prove 
detrimental to the navigation or flowing of the river, it must be 
discharged into lighters to be carried away. If the soil is firm, 
and the sheeting piles have gone six or eight feet into it, that soil 
may be dug away, if necessary, to about half their depth. But 
this is a delicate operation, requiring judgment and experience, 
for if too much of the inner soil is removed, the (eet of the sheet- 
ing piles may be forced inwards by the external pressure of the 
water, and the whole dam may be blow?i up^ as it is called, and 
destroyed. Whenever, therefore, it is found that the inner founda- 



OF COFFER-DAMS. 627 

tion has to be sunk to near the bottom of the dam piling, a coun- 
ter dam must be formed; that is, a rectangle of strong she^iting 
piles must be driven parallel to the inside of the main dam, and 
about two feet within ifr. These new sheeting piles should extend 
several feet lower than the dam piles, and be strengthened with 
string pieces and braces, and now the space between this counter 
dam and the external dam being filled up with gravel, clippings 
of stone, and any hard materials well rammed, so as to resist and 
restrain the outer piles from bulging inwards, the excavations 
' may proceed downwards, in this internal dam, even below the 
bottoms of the main piling. This was the case in the building of 
Bewdley stone bridge, over the river Severn, in Worcestershire, 
in England. The foundation was not found trustworthy at the 
depth to which the dam piles extended, but by this expedient Mr. 
Provis, the Engineer, was enabled to carry the foundations about 
five feet below the extreme bottoms of the dam piles, and to seat ^ 
them on a bed of rock. It sometimes happens that the cofFer-dam is 
constructed upon sand, gravel, or other porous ground, and that the 
water will rise from the bottom and prove very troublesome; and 
in this case the internal dam may prove useful by filling the space 
between it and the main dam with puddle, and leaving as small a 
quantity of surface as possible for the water to rise through. 

1128. In ordinary cases when the soil at the bottom of a coffer 
dam, after it has been dug into for a depth of three or four feet 
and made level, is not found hard enough to base the work upon, 
it must be piled with rows of piles, with caps or sleepers upon 
them, and be treated in every respect like the piled foundations 
before described (1119). 

1129. All piers for bridges ought to have considerable footings, 
or cover much more ground at the foundation than when they ap- 
pear above water, not only to give them greater stability but be- 
cause the offsets are frequently useful as a means of supporting 
the timber centres upon which the arches are to be built. The 
length of piers must depend upon the width of the bridge; but 
their breadth should be as small as possible, consistent with neces- 
sary strength, in order that they may not choke up the width of 
the river. This is one of the great improvements in modern 
bridge building, for formerly there appears to have been a doubt 
as to the strength of the arch, while excessive and useless strength 
was given to the piers, of which London Bridge is an example. 
The ancient bridge had no less than 20 arches to pass over a 
width of 900 feet of water; and these small arches rested upon 
such immense piers that they contracted the water-way to 194 
feet. This edifice has been replaced by a new bridge of five 
arches, with a water-way under them of 692 feet, so that the four 



628 FOUNDATIONS IN WATER. 

piers and two land abutments now only abstract 208 (eet from tbe 
width of the river. For the same reason that piers should be 
narrow, so likewise their ends must not terminate in abrupt flat 
surfaces, but should be made sharp, to cut or divide the water and 
deflect it under the arches. In navigable rivers the form of the 
ends is important, since they ought not to present sharp points 
that may be broken off by vessels running against them, or flat, 
which might injure the vessels. Some difference of opinion exists 
as to the best form to be given to them, and accordingly they 
occur of different shapes in different bridges, but the general forms 
on their plans are the equilateral triangle, the semicircle, or the 
true Gothic arch. This last figure was adopted in the new Lon- 
don Bridge, and appears the best; for the point is stronger than 
in the triangle, and its curves run imperceptibly into the right 
lined direction of the piers without any angle to be broken off, or 
to injure vessels, or produce an eddy in the flowing water. 

1130. The pumping of a coffer-dam is always an expensive 
operation; ,for, however well it may have been constructed, there 
are few soils that will admit the driving of piles but what will 
permit a considerable quantity of water to percolate and rise up- 
wards through the bottom. A stiff clay soil is almost the only 
exception. Pumping, therefore, when once begun has to be con- 
tinued, day and night, without the slightest intermission; and all 
stones, timber, and other materials should be cut and laid, or fit- 
ted together before the pumping begins, in order that they may 
be fixed in their proper places without a moment's delay, so soon 
as the water is sufficiently drained to render the bottom accessi- 
ble. Where piling has to be driven in a foundation that may be 
done as well through the water as not, provided the pile heads 
are kept above it, and the piles may also be cut off to a level 
under water by machines constructed for that purpose, consisting 
of a saw arranged in a frame, which is firmly bolted to the top of 
the pile. But to examine the pile heads, lay down the sleepers 
or grillage, and place the lower stones — the water should be so far 
removed as to render the piles and soil visible, or at any rate, for 
the workmen to stand upon them in their water-boots, and feel 
them with their hands. For a short period, therefore, before 
getting in the commencement of a foundation, it may be necessary 
to strengthen the clearing force as much as possible, by applying 
hand pumps, or bailing the water out with buckets in addition to 
the engine or other prominent pumping power, should that be 
deficient. But this extra exertion will be but of short duration, 
provided every thing has been properly prepared and got ready, 
and a strong gang of good workmen are concentrated upon the 
spot; especially as on such occasions the work is carried on, if 



OP COFFER-DAMS. 629 

necessary, by torch light in the night as well as in the day. 
In pumping a coffer-dam, or other wet foundation, the suc- 
tion pipe of the pump is so constructed that it can be lowered 
as the excavation goes down; and as soon as the bottom is 
laid dry, or as nearly so as possible, a hole of a foot or more 
in depth must be sunk for that pipe to pass into. This hole 
is called the sumpy and its object is to drain the adjacent founda- 
tion by its greater depth. The wind-hore, or lowest pipe of the 
pump should stand in a wicker-basket in this hole, to prevent 
chips, pebbles, and other small bodies entering the pump, as they 
would impede its due action. 

1131. When a coffer-dam is constructed in a tide water, it 
should have an orifice through its side a little above low water 
mark; but which can be closed by a water-tight sluice or gate. 
By means of this, should the dam, at any time, become full of 
water by cessation of pumping or other cause, such water can be 
let off at low water, to the level of the bottom of the sluice; 
whereby all the pumping that would be necessary for this object 
is saved. Besides it is also desirable, whenever possible, to make 
the pumps deliver their water through this hole, instead of raising 
it over the top of the dam, for every foot in height that can be 
saved in delivering the water will be sensibly felt in the power 
and expense of working the pumps. 

1132. As soon as the lowest course of stone- work has been got 
into its place and is fixed, the ground around it should be care- 
fully rammed in, or puddled around, especially when the bottom 
yields much water; and that puddling will often require to be 
boarded over to keep it in its place; and the same caution is ne- 
cessary with each succeeding course, until the work is brought 
up to a level with the general bed of the river; but as earth 
should be piled in the coffer-dam above this height, it might 
become an impediment to the flow of the river when the dam is 
moved away. As soon as the pier or other work is built above 
the height the water reaches to, all pumping is, of course, discon- 
tinued; and in tide waters, the men very frequently work what is 
called tide-work, instead of working constantly, i. e. the water is 
permitted to run out at the sluice, as the tide descends. At low 
water it is shut out, and the workmen begin their operations, and 
continue them until the water rises so high as to prevent their 
proceedings, and this will seldom happen until some hours after 
high water, even though no pump may be working, provided the 
dam and its bottom are tolerably water-tight. 

1133. The coffer-dams are permitted to remain until the 
arches are finished, because their flat tops afford most convenient 
landing places for stones, timber, and other materials for building 
the superstructure, and scaffolding is erected upon them for that 



630 FOUNDATIONS IN WATER. 

purpose. They are also highly useful as standing places while 
fixing the centring for the arches, and which frequently derive 
part of their support from them; and, lastly, they may become 
useful in the event of any settling or accident that may befall the 
piers from the weight or strain of the arch when built, which 
may render it necessary to examine, and, perhaps, to repair such 
piers, which may be laid dry for that purpose while the dams re- 
main; but would be impossible, or very expensive after their re- 
moval. When, however, it is ascertained that the dams are quite 
done with, they are then removed, either by drawing the piles 
out of the earth, or by sawing them off as near as possible to the 
bottom of the water. The last is the most usual and certainly 
the best practice, because drawing piles frequently loosens the 
soil about the foundations and may do irreparable mischief. The 
only object of drawing piles is to save the timber, and remove 
obstructions to navigation, and when they are sawed, the tops are 
saved, while the bottoms, if drawn, will seldom or ever pay by 
their value for the labour and apparatus necessary for their ex- 
traction. All large fenders or distant piles may be drawn, and 
the best means of doing this is by the hydraulic jack, a machine 
constructed on the principle of the hydraulic press, and which was 
used for this purpose in a very satisfactory manner at the Water- 
loo Bridge of London. 

1134. A great waste of large timber necessarily occurs in the 
construction of all large stone or other bridges, because the dams, 
fender piles, centring and lagging, temporary bridge scaffolding, 
&c. are all useless as soon as the bridge is finished. But such 
timber is generally large and not materially maimed, as all the 
works should be put together with screw-bolts. To meet this 
waste, a bargain is sometimes made with the contractor that he 
shall take away and allow for all spare timber and iron, at stated 
prices, on the conclusion of the work; or else it is usually sold by 
auction, being all convertible to similar work, or smaller purposes. 

1135. When the bottom of the water is of hard and smooth 
rock into which piles cannot be driven, or where it is of sand, or 
such soil as would inevitably let water pass readily through it, 
coffer-dams cannot be constructed, or if made could not be kept 
dry by almost any pumping power. In which cases the caissopn 
mode of building must be adopted. A caissoon is a large chest of 
strong timber made water-tight, so that it will float like a boat, 
and the masonry or brick-work is carried on within it, until by 
its weight it sinks to the bottom. The bottom of the caissoon, of 
course, remains forever under the bottom of the pier, and becomes 
its foundation. It is a French contrivance, and is held in high 
estimation by the Engineers and Architects of that nation; but 



OF CAISSOONS. 631 

its chief advantage is the facility and accuracy with which a cais- 
soon can be built on dry land and be afterwards transported, 
piece meal, to the water, upon which it is put together. It is 
much cheaper than a coffer-dam, as the timber with which it is 
Imilt is not only thinner but less in quantity, as it has but one wall 
instead of two. The labour of pile driving is saved, and from the 
greater perfection that can be given to the workmanship of the 
joints it may be made as water-tight as a boat or ship; and it 
therefore saves a great expense in pumping. The chief danger 
attending its use is that it does not afford the same examination 
and proof of the soundness and sufficiency of the earth foundation 
that is obtained in the coffer-dam, unless the diving bell is used 
for the Engineer and his assistants to descend to the bottom, nor 
can the bottom be cleared of its soft mud or be made level except 
by the use of a machine called a dredging-machinef which is built 
upon a large barge, and consists of a number of iron boxes attach- 
ed to an endless chain, which is strained in a strong oblong timber 
frame fixed in a sloping direction to the side of the barge, with 
its lower end resting upon the bottom of the river. , The edges of 
the iron boxes act like scrapers against the bottom of the river, 
and bring the soil up and discharge it into lighters moored to re- 
ceive it, the boxes being kept in motion by a steam-engine upon 
the barge. These machines are now in common use upon all such 
navigable rivers as are found to fill up by deposits of sand or 
mud, and are found very efficacious for cutting straight channels 
for the water to run in, thus preserving the necessary depth for 
navigation. 

1136. The earth foundation being rendered flat and smooth by 
this machine or otherwise, must be piled, if necessary, and the 
piles being cut off' close to the ground, the foundation will be pre- 
pared for receiving the bottom of the caissoon, which is a strong 
grating of timber, floored over, and so contrived that the vertical 
sides which form it into a box, can be detached from it when ne- 
cessary. The most considerable work, in which the caissoon mode 
of building has been followed, as the writer believes, is Westmin- 
ster Bridge, London. The river at the site of the bridge is 1,223 
feet wide, and the bridge, which consists of fifteen semicircular 
arches, supported on fourteen piers and two abutments, is built 
entirely of Portland freestone. Its width is forty-four feet; the 
centre arch is seventy-six feet span, and the others diminish four 
feet each as they approach the shores. It was built by M. La- 
belye, a French Architect and Engineer, between the years 1739 
and 1750, and cost ^389,000. From the nature of the ground in 
this place, as ascertained by several other bridges built near it, 
there could be no objection to constructing coffer-dams; but the 



632 FOUKDATIONS IN WATER. 

caissoon was adopted in this case from a persuasion that it would 
be the cheapest mode of construction. This does not appear to 
have been proved in the sequel, for Blackfriars Bridge built near it, 
and which is 995 feet long, only cost ^6152,840; and the Vauxhall 
Bridge above it, and 860 feet long, formed of nine cast iron arches 
on stone piers, was finished for ^150,000. These last two bridges 
were both built in coffer-dams, and although they are much 
shorter and have fewer arches, yet the difference in expense is 
not at all in the ratio of their length. Westminster Bridge also 
shows that the caissoon plan is not the best in point of security, 
and that the soil of the foundations should be more scrupulously 
examined than is possible without a coffer-dam, or some means of 
getting down to it in a nearly dry state; for after this bridge was 
finished one of the piers sunk so much deeper into the ground than 
the rest, that it was feared two arches would be lost, but they 
were saved by an ingenious device, applied in good time, and no 
symptoms of failure have since been observed. 

1137. We cannot give a better account of the formation of 
caissoons, than by extracting that part of the history of the build- 
ing of Westminster Bridge which relates to them, as published by 
M. Labelye himself The caissoons had flat bottoms with six per- 
pendicular sides, viz: two long ones, parallel to each other, and 
two shorter ones at each end, placed in an angular position to 
each other, so as to produce an irregular or elongated hexagon in 
plan. Their form was, therefore, nearly similar to the piers to be 
built in them, and parallel to their outsides. He says, "each 
caissoon consumed about 150 loads of fir timber. Their dimen- 
sions were nearly 80 feet from point to point, and 30 feet wide 
across between the sides. They were 10 feet deep and formed of 
timbers laid horizontally over each other, pinned with oak tre- 
nails, and framed together at all corners except the two salient 
angles, where they were secured by proper iron-work, which 
being unscrewed, would permit the sides of the caissoon, had it 
been found necessary, to divide into two parts. These sides were 
planked across the timbers, inside and outside, with 3 inch planks 
placed vertically. The thickness of the sides was 18 inches at 
the bottom, and 15 inches at top; and to strengthen them more 
effectually, every angle, except the two points, had three oak 
knee timbers, firmly secured by bolts. The sides were fastened 
to the bottom, or grating, by 28 pieces of timber called straps, 8 
inches broad and 3 thick, on the outside, and 18 within, the lower 
ends of these straps being dovetailed to the outer curb of the 
grating, and were kept in their places by iron wedges, the pur- 
pose of which was that when the pier was built so high as to 
stand above low water mark, and the sides were no longer neces- 



OP CAISSOONS. 633 

cessary, by drawing these wedges, the sides would be released and 
they would rise by their own buoyancy, leaving the grating under 
the foundation of the pier." 

"The pressure of the water upon the sides of the caissoon was 
resisted by a ground timber or ribbon, 14 inches wide and 7 inches 
thick, pinned down to the grating close to the sides; and the top 
of the sides was secured by a sufficient number of beams laid 
across, which being floored, served for the workmen to stand upon 
for hoisting the stones out of hghters, and lowering them into the 
caissoon. The caissoon was also provided with a sluice to admit 
the water. 

1138. "The method of working was as follows: a pit being dug 
and levelled in the proper situation for the pier, of the same shape 
as the caissoon, but about 5 feet wider all round, the caissoon was 
'floated to its position, a few of the lower courses of the pier were 
built in it, and it was then sunk once or twice to prove the level 
of the foundation. Then, being finally fixed, the masons worked 
in the usual method of tide-work. About two hours before low 
water the sluice of the caissoon, (kept open till then, lest the wa- 
ter flowing to the height of many more feet on the outside than 
on the inside should float the caissoon and its contained work out 
of its true place,) was shut down, and the water pumped low 
enough, without waiting for the low ebb of the tide, for the ma- 
sons to proceed with their work. This continued until the tide 
had risen to a considerable height, the sluice was again opened, 
and the water admitted. And as the caissoon was purposely 
built but 16* ^eet high to save useless expense, the high tides flow- 
ed some feet above the sides, but without damage or inconve- 
nience to the work. In this manner the work proceeded until the 
pier rose above the top of the caissoon, when the sides were float- 
ed away to serve at another pier.'' 

1139. The other five large bridges of London, called the new 
London, the Southwark, Blackfriars, Waterloo, and Vauxhall, all 
built since Westminster Bridge by Messrs. R. Mylne, John Ren- 
nie, and James Walker, have been constructed by coffer-dams. 
These bridges were all constructed at a period when the closest 
attention was paid to science and perfection of workmanship, and 
this offers a conclusive argument that the coffer-dam mode of 
working is preferable to that by caissoons. An experiment was 
however made at the commencement of Vauxhall Bridge, before 
it was put into the hands of Mr. Walker, upon a new kind of 

* This is an evident contradiction, as the sides are at first stated to be 10 
feet high. It may be an error of the press, and that the height should be 10 feet or 
16 feet in both places. Or perhaps 10 feet of strong walling was first construct- 
ed, and 6 feet more built upon it; but this does not appear from the description. 
80 



634 OF ARCHES. 

caissoon. The ground was levelled and prepared, and a grated 
and boarded bottom like that of other caissoons was prepared, 
and floated like a raft over the place where it was to be sunk. 
It was retained in that position by a number of straight piles 
driven at certain distances around it, but not touching it, so that 
the raft or bottom could float, and rise and fall with the tide, or 
pass to the bottom of the river without impediment. Instead of 
using wooden sides, to be afterwards detached, the external wall- 
ing of the pier itself was built in brick-work laid in cement, but 
was kept of such thickness, by leaving the middle of the pier hol- 
low, that the weight of these walls should be incapable of sinking 
the platform so deep in the water as to permit the water to flow 
over the tops of the walls which were carried up as the platform 
sank down. It was thought the platform could be lowered to the 
ground in this manner, and would exclude the water from the 
central cavity; or that what percolated might be pumped out; 
and as soon as the hollow pier was firmly seated on the ground, 
the inside was to be tilled in with solid work. The expedient was 
ingenious, but it failed, because if solid work was filled in to pro- 
duce strength the pier sunk too rapidly, and by keeping it hollow, 
to insure flotation, the lateral pressure of the water burst in the 
side walls, and the whole was reduced to a mass of ruins. 

1140. The most difficult case that can occur for the construc- 
tion of piers, is when the bottom of a deep river is of hard rock 
that defies the entrance of piles, and is at the same time so rough 
and irregular as to preclude the possibility of seating the bottom 
of a caissoon. In such places no bridge can be formed unless it 
consists of a single arch extending from one side of the river to 
the other; or the formation of the river is such that its course can 
be diverted from its channel at the place where the bridge is re- 
quired, by the excavation of a new channel to draw oflfits water 
for a time, and reduce its depth to such an extent that the rocky 
bottom is made accessible, and that dams of timber and clay may 
be made from one rock to another, in order that the bottom where 
the bridge is to be built may be rendered dry enough for working 
upon; but this produces an expense so great that it is rarely re- 
sorted to. 

Section II. — On the Construction of Stone and Brick Arches, 

1141. Having constructed our side walls for the support of the 
arches intended to be built, or the necessary pillars or piers, in the 
event of being about to construct a bridge, or aqueduct, and hav- 
ing fixed the necessary centring for sustaining the arch in its pro- 
gress of building between them according to the directions already 



ORIGIN OP ARCHES. 635 

given; we have next to take the arch itself under consideration, 
and in doing so shall divide the subject into four distinct heads. 
1st. The form of the arch and names applied to the different parts 
that compose it. 2ndly. Its stability and pressure. 3dly. The 
materials of which it is to be formed; and 4thly. The methods of 
putting those materials together. 

1 142. The form and dimensions of the arch must of course have 
been decided upon before the centring, upon which it is to be 
built, could be constructed; consequently it may appear that this 
part of the subject should have been noticed in the chapter that 
describes centring. But inasmuch as a centre may be made of any 
form and dimensions, and as the stability, equilibrium and strength 
of the arch depends upon its own formation after the centring is 
withdrawn, this consideration belongs properly to the arch itself, 
and has accordingly been reserved for this chapter. 

1143. The arch is comparatively a modern invention, for no 
trace of it is found in the architecture of ancient Egypt or Persia, 
or in the Druidical remains of England, and the lintel or long 
straight stone appears to be the only expedient resorted to for 
forming a top or covering to doors or windows over which it was 
intended to carry on the building. In the pyramids of Egypt long 
passages or galleries are found which travellers have described as 
arched; but they do not exhibit the regular or legitimate form of 
the arch, but are formed by what modern workmen called over- 
sailing or corhling over. The side walls are carried up perpen- 
dicularly to the necessary height, and then instead of continuing 
to build them in a vertical direction, each succeeding course of 
bricks or stones is made to project beyond the perpendicular on 
each side, taking care that the centres of gravity of each stone 
shall be within the perpendicular line of the face of the wall, so 
that these rows of stone may have no tendency to fall. The next 
courses above each over-sail in the same manner, which would 
have the effect of bringing the centre of gravity of the upper work 
so far before the walls that it would fall, but this may be prevent- 
ed by carrying up solid work upon the tails of the projecting 
stones to such an extent that its weight shall be superior to that 
of the over-sailing work; the projecting stones being long enough 
to reach into such solid work. In this manner the two projecting 
masses of work may soon be made to meet and support each other, 
when there will be no danger of any of it falling, of which the 
existence of such passages in some of the oldest buildings in the 
world afford ample testimony. This mode of construction is 
shown by Fig. 262, which represents a transverse section of such 
a passage. In this mode of working the opening is covered by 
causing the covering-stones to corhle over on one or both sides as 



636 OF ARCHES 

desired, provided one perpendicular wall is higher than the other. 
Thus instead of taking the wall b as one of the sides, we may- 
imagine the dotted line c d to represent a side, and then the cover- 
ing will only extend over from the wall a, forming a kind of half 
arch. 

This construction has however neither the form or principle of 
the arch, and the invention of this beautiful and useful auxiliary 
to the building art is generally given to the Greeks, as arches are 
met with in some of their most ancient temples. But even in 
these, the arch does not appear to have been introduced, as in the 
more recent constructions, for ornamental purposes, but merely 
for obtaining strength; for such arches were frequently hidden in 
the interior of walls, or used for covering drains. The pediments 
or triangular forms of the ends of the roofs of the Greeks may 
probably have led to, or suggested the construction of the arch, 
for the two sloping rafters of a roof leaning against each other 
will afford mutual support, provided their lower ends are prevent- 
ed slipping outwards; and if two strong stones should be so dis- 
posed, they may be built upon and will bear a great load. 

1144. The principle before adverted to in carpentry of intro- 
ducing a horizontal stretching beam between the upper ends of 
two struts, may also be resorted to in stone-work, and then we 
shall have a figure approximating more closely to the form of an 
arch; and by supposing each of these stones to be divided and 
placed so as to present several sides of a polygon, an arch will be 
produced. 

1145. The semicircular form of arch is the one that was 
adopted by the Greeks, and is likewise the form met with among 
the Saxon buildings in England, and this is also at the same time 
one of the strongest and most elegant forms for an arch. Its 
strength depends upon its springing or commencing upon a hori- 
zontal line which is its diameter; consequently a great part of the 
load acts perpendicularly on in the direction of gravitation; and 
therefore it has little tendency to spread, or exert lateral pres- 
sure against its abutments; and from the beauty of its form, it is 
the arch most frequently made use of by Architects for ornamental 
purposes. It has the same advantages when applied to bridges, 
but is not always admissible into their construction on account of the 
height it extends above its springing, which must always be equal 
to its radius; and this requires the roadway over the bridge to be 
so elevated, particularly in a bridge of a single arch, that the 
slopes, to reach the summit, may be inconveniently steep, unless 
the side banks of the river are considerably elevated above the 
water. 

1146. In order to obviate this inconvenience an arch formed 



VARIOUS FORMS OF ARCH. 637 

of a segment of a circle, or a semiellipse, may be adopted; and 
accordingly these forms are very frequently resorted to, and have 
their advantages and disadvantages. Both of them consume much 
less material to span the same opening than the semicircle; but 
the lateral pressure of the segment (which includes all arcs of 
circles containing less than 180°) is very great and increases rapid- 
ly as the angular measure of the length of the arc is diminished; 
consequently it requires buttresses or supports of greater strength 
and solidity to resist this force. 

1147. The elliptic arch, on the contrary, from the flatness of 
its crown, becomes weak in that part, unless it is properly weigh- 
ed down or loaded on its haunches, so as to prevent their rising, 
which is necessary to the descent of the crown. The production 
of this perfect equilibration of the parts of an elongated elliptic 
arch is therefore a matter of great importance and nicety. 

The above mentioned are the forms of arch usually adopted in 
modern practice for constructing bridges and aqueducts, or for 
covering openings above which it may be desirable to build, and 
when strength and stability are required. But in architecture 
another variety of arch is frequently introduced on a small scale, 
such as covering over doors, windows, or other small openings, 
called the scheme or skene arch, and sometimes the camber arch. 
This partakes very little of the properties of the arch, and is used 
for ornament rather than strength, because an ordinary lintel 
composed of the same materials in one piece, and of the same di- 
mensions as the arch, would, in most cases, exceed it in strength. 
This arch, as usually executed in bricks and stone, is shown by 
Fig. 263, in which it will be seen that its top and bottom deviate 
very little from right lines, though it is customary to give them a 
slight camber, or bending upwards, but so slight a one as to be 
scarcely perceptible to the eye; such, for example, as a rise or 
versed sine to the lower line of the arch of from half an inch to 
an inch in four feet. 

The only circumstances therefore that entitle this construction 
to the name of an arch, is the wedge-like form of all the pieces 
that compose it. Bricks are sold under the denomination of cut- 
ters or rubbers for building these arches, because each brick has to 
be cut with a saw, or chopped by a small axe made for the pur- 
pose, and has its sides afterwards rubbed or ground upon a stone 
until it is made smooth, and accords perfectly with angular lines 
that have been previously set out upon a platform. Brick arches 
of this kind are, from their mode of construction, called guaged 
or rubbed arches, and they never extend through the entire thick- 
ness of a wall, but being used for ornament only, are confined to 
four inches in depth or the breadth of a single brick, and the 



638 OP ARCHES. 

hinder part of the wall consists of an ordinary rough arch, or a 
stone or timber lintel. 

1148. The term, rough arch, when applied to brick- work, 
means an arch formed of bricks used in their ordinary form with- 
out being rubbed or cut into wedge-like forms; and is therefore 
opposed to the term cut or rubbed arch. 

1149. Another form of arch has yet to be mentioned. It is 
generally, though improperly called the Gothic arch, notwithstand- 
ing it has been clearly determined that this arch was neither in- 
vented or used by the Goths in their constructions. It would, 
therefore, with greater propriety be called the pointed style of 
architecture, for this arch is formed by the intersection of portions 
of circles, and its crown is always an angular point more or less 
obtuse. The pointed style originated in Italy about the middle of 
the 12th century, and was soon afterwards introduced into France 
and Great Britain, where it arose so much in estimation, and was 
so frequently adopted, that some writers have improperly called 
it the old English style, a title that cannot belong to it, since it 
was imported from the continent of Europe. Its introduction, and 
the preference it obtained over the previously introduced Grecian 
style, appears to have given great offence to some of the early 
writers on architecture, and they applied the term Gothic to it, 
in derision and contempt, notwithstanding which this name has 
been very generally preserved and attached to it. Of late years 
the Gothic style has had many advocates and admirers among 
men of acknowledged taste, and a fashion has been established of 
imitating it in modern buildings. As its existence was long ante- 
cedent to the discovery and civilization of America, of course no 
original examples of it are met with in the United States, nor do 
I believe that a truly good and legitimate copy of this style of 
building has been constructed in this country, so as to impress 
the spectator wdth those ideas of beauty, grandeur, and magnifi- 
cence which every one acknowledges to feel when he first enters 
the Abbey of Westminster or King Henry Vllth's Chapel, in 
London, the Minster at York, or the Cathedrals at Milan, Brus- 
sels, and many of the cities of Europe. 

1150. On the first introduction of the pointed arch no particu- 
lar rule appears to have been laid down for its formation, further 
than that it was always formed by the segments of two circles 
springing, or commencing from a horizontal line, and meeting at 
the crown or apex. Its several forms are shown in Fig. 179 of 
Plate VI. Thus the two arcs that form the arch are struck from 
the two centres a and h, each of which are placed the entire width 
of the window beyond its two sides, with radii a c and h d extend- 
ing from the centres to the opposite side of the opening, and this 



ON SETTING OUT ARCHES. 639 

gives the arch great height and an acute point, on which account 
this arch is frequently styled lancet pointed. 

In the principal window the arcs are struck with radii ef and/e 
equal to the width of the opening, from centres e and/, in the vertical 
lines that form its sides; and if we wish to divide the opening of 
such windows into two or more compartments, as by the vertical 
lines, we must head or finish these with segments having the same 
radii as were used for striking the principal or external parts. 
Vertical divisions, like g, whether in their straight or curved parts 
are, in this style of building, called mullions or mwwmows, while all 
divisions that run horizontally are called transoms. Both these 
arches, as well as several other varieties of figure, were at first 
used indifferently or without rule; but towards the close of the 
13th century the second form prevailed, and was generally used. 

In the middle of the 15th century the pointed arch underwent 
a great change in England, and became much lowered, and its 
apex much more obtuse; for now instead of being formed by the 
meeting of two segments of circles, four were used; two being of 
large and two of small radii, as in the doorway of the figure which 
the French call the arch of four centres. Many examples of 
it occur in the Royal Palace of St. James, London, and in many 
other buildings of the same date. The radii of curvature differ 
so much in various arches of this form, that it is difficult to say 
that any precise rule was followed for their formation. In some 
examples the bottom of the door- ways appears to have been divided 
into four equal parts, and the large curves to be struck from the 
points h h each at one quarter of the width of the opening from 
its sides, the two other small segments that form the springings of 
the arch are from the points i i, which are perhaps arbitrary, 
though in some cases their radius appears to be one-eighth of the 
width of the opening. During the reign of Henry VIII. the 
pointed style ceased to be used in England, as a common or ordi- 
nary mode of building; consequently all erections of this kind, 
since that period, may be considered as occasional imitations, sug- 
gested by the taste or fancy of their constructors. 

The above constitute all the forms of arch usually resorted to 
for the various purposes of building, but arches may be formed in 
a variety of other geometrical curves, such as the catenarian, cy- 
cloidal, parabolic, &c. 

1151. Our next object must be to describe the mode of setting 
out arches of their real size, for the purpose of laying out and con- 
structing the ribs of the centring. In small arches this is an easy 
operation; but in large ones, the radii of which are beyond the 
reach of compasses of any description, it is more difficult, or rather 
requires great nicety. A slight rope fixed in the centre of curva- 



640 OP ARCHES. 

ture, and of a length equal to the radius required, and having its 
opposite end carried round the portion of curve to be described, 
while it is kept evenly strained or stretched, suggests itself as the 
most convenient method of describing a portion of a large circle, 
because a pointed piece of chalk or steel scribing-point attached 
to the end that moves, will describe any portion of a circle upon 
a platform, and this is the process usually adopted, w^ith the sub- 
stitution only of a wire for a rope. A rope would not answer the 
purpose, because its elasticity would allow of too much expansion 
and contraction, which would be augmented by its twisting or un- 
twisting, and its hygrometric property of changing length when 
damp or dry. Indeed there are many objections to a rope which 
it is needless to mention, while a black or soft drawn iron wire of 
about ^th or y^^th of an inch in diameter obviates most of them. 
A black or soft iron wire is mentioned because hard wire, which 
is always polished, is more unmanageable. It has a springyness 
about it which renders it difficult to draw it straight without the 
exertion of great force, while a black or annealed wire is strong 
enough to resist such force as is necessary to keep it straight and 
stretched without extending in its length, and will yield to and 
preserve any form that is given to it. Wire is subject to expan- 
sion and contraction by heat and cold, but it will be in use so short 
a time that nothing need be apprehended on that score. With 
such a wire, therefore, a semicircle or an arc of a circle may be 
very correctly struck upon the platform before described, (1094,) 
by using due care and precaution. By the same wire a right 
line must first be laid down extending from the centre of curva- 
ture to the crown or summit of the intended arch, cutting or 
dividing the arch into two equal portions, and then another 
line must be drawn correctly at right angles to this first line, to 
represent the diameter (or chord, as the case may be) of the in- 
tended arch for the purpose of setting out the footings or abut- 
ments of the arch. That done, three parallel curves have to be 
described; the extreme or outermost one representing the under 
side of the arch as it is to appear when finished. The second one 
as much within the first as is equal to the thickness of the lagging 
proposed to be used, and which will of course represent the out- 
side convex surface of the ribs of the centre, and the inner one 
will represent the concave or under side of such ribs. 

1152. No difficulty will therefore arise in setting out any arch 
that is circular; but this is not so much the case with arches that 
are elliptical, and on this account the true ellipse is not often made 
use of, but other figures are resorted to which approach very 
nearly to the elliptical form, notwithstanding they are portions of 
circles. The manner of describing a true ellipse by a thread, the 



OF ELLIPTICAL ARCHES. 641 



\ 



two ends of which are attached to the two foci, is well known, 
and this principle may be adopted and extended with considera- 
ble accuracy, to a large scale, by making use of a flexible iron 
wire instead of a thread, and attaching its two ends to the two 
points upon the platform which have been previously selected and 
fixed upon for the two foci. 

There are several methods of producing curves that coincide so 
nearly with the form of the ellipse that they are frequently made 
use of in bridge building, and we give that generally used by, 
artists. Draw a horizontal line m m, Fig. 264, to represent the 
transverse diameter of the oval and springing line of the arch, and 
upon the centre of this raise the perpendicular nop. Take oflf 
the extent of the intended rise of the arch on a scale of equal 
parts, and transfer it into its proper place upon the perpendicular 
line, as from o to n. Then with radius o n from o as a centre, de- 
scribe the semicircle qnr, and use its diameter ^ r as a base upon 
which to form the equilateral triangle q r p; prolong the two 
sides that extend to the horizontal line indefinitely as from r to ^ 
and q to s, and the three angles of the equilateral triangle will be 
the three centres from which to describe the three arcs of circles 
of 60° each. Consequently with radius p n, from centre jo, describe 
the arc s n t^ making it extend from one prolonged side of the 
triangle p s io the other p t. Then from r and q as centres, and 
with radii equal to the distance between those points, and the 
points where the last mentioned arc cuts the prolonged sides of the 
triangle, as ^ 5 and r t, describe the two arcs s m and t w, and the 
curve will be complete. 

1153. In the last example the oval is made exterior to or cir- 
cumscribing the semicircle; but by the same chain of reasoning it 
may be inscribed within it, but if this is desired, the radius of the 
semicircle must be made equal to the semitransverse, instead of 
the semiconjugate diameter, as follows: Fig. 265, first draw a 
horizontal line v u equal in length to the semitransverse diameter 
of the oval or span of the arch, and with that distance as radius 
describe the quadrant of a circle w x y u from centre v. Divide 
this arc into three equal parts 'as> w x y and «, and join x vhy -a, 
right line in order to determine the position of the next line y z, 
which must be drawn from point y parallel to a; t; and be prolong- 
ed until it intersects the perpendicular zu <y in the point z, and then 
will the points a and z be the two centres from which to describe 
the required oval, beginning with a as a centre and with radius 
a u describe the small arc u b. This will give a fixed point b in 
the line z y, and from 6 to z will be the radius of the large curve 
to be struck from centre z. In this example only half the figure 
is given, and only half the arch described; but the other half may be 
81 



642 OF ARCHES. 

completed by repeating the same operations on the left hand side 
of the vertical line w v z. 

In these examples the curves produced approach very nearly 
to the true ellipse, but are all a little without or are circumscribed 
upon that figure and only touch or coincide with it at three 
points, viz: the two springings, and the top or crown of the arch. 

1 154. Another expedient often resorted to for producing an oval 
of less eccentricity than the above is as follows, Fig. 266. Draw 
a right line c d, equal in length to the transverse diameter of the 
curve desired, and divide this line into three equal parts, as at the 
points e and/, and from each of these points as centres, in succes- 
sion draw the two circles c hfg and e i dg, with same radius/ of 
equal one-third of the length of the line and they will intersect 
each other at point g^ from which draw two right lines or diame- 
ters^ hf g i. Then with radius equal one of these diameters g A, 
from centre g describe the arc h i joining it to the previously ex- 
isting arcs c h and i d, and the arch or half oval will be com- 
plete. 

1155. We will now describe a more perfect process invented 
by Professor Robison, which coincides with the true ellipse in 
eight points, and furnishes the artist with the means of drawing 
an infinite variety of ovals. See Fig. 267. Draw a right line ^ A; 
to represent the transverse axis or diameter of the proposed oval, 
and upon the centre of it erect the perpendicular / m for the 
conjugate axis crossing j km p which is the centre of the oval. 
Then fix on the rise or semiconjugate diameter you wish to give 
the oval, and having measured this on a scale of equal parts, set 
off that distance on the perpendicular, as from p to 7i, and like- 
wise transfer it from p io q on the horizontal line. Then draw a 
circle j n q passing through the three given points j n q (74) and 
now if from any point r short oij in the arcj rnhe drawn a chord 
r n and if a line r, 5, m be drawn, making the angle nr s equal to 
r w JO, and meeting the two axes or diameters in the points s and m. 
Then s and m will be the centres of two circles, which will form 
one quarter j r n of an oval, as dotted in the figure; and being 
thus in possession of the two necessary radii, the other half of the 
curve may be obtained by setting off the distance p s towards k 
in order to determine the centre of the second small arc. 

1156. Having thus shewn how the forms of arch most frequently 
made use of may be obtained, we shall in the next place examine 
the means of obtaining another form which is frequently referred 
to by writers, though seldom met with in practice. 

Towards the close of the last century, the subject of the con- 
struction of arches engaged the attention of some of the most em- 
minent mathematicians of Europe, and Dr. Hooke affirmed that 



THE CATENARIAN ARCH. 643 

the festoon or figure which a perfectly flexible chain or rope of 
equal weight throughout would dispose itself into, when suspend- 
ed by its two extreme ends, would, if inverted, give the proper 
form for arches formed of parts which touched each other in the 
same points, because the forces with which they would mutually 
press on each other in this last case, would be exactly equal and 
opposite to the forces with which they pull each other in the case 
of suspension. 

1157. This principle is strictly just, and may be extended to 
every case that can occur; but it produces an equilibrium that 
will admit of no kind of disturbance. If the chain is not of equal 
weight in every part or link, it will produce a curve that will not 
be similar and equally strong on its two sides. And if the chain 
is of equal weight throughout, and in a state of perfect equilibrium 
with itself in the first instance, so as to produce a perfect curve, 
and it is afterwards purposely loaded with different quantities of 
weight in different parts, the curve will be varied in its form, 
although it will take up a new state of equilibrium; for an effect 
of composition and resolution of forces will occur, and as each 
link of the chain may be considered as a pivot about which its 
parts can turn, so the form and symmetry of the curve will be 
destroyed, and it will become irregular, notwithstanding that it 
remains in a state of equilibrium with respect to itself. As, how- 
ever, bridges are unequally pressed down by the earth placed 
upon them to form the roadway, as well as by the various 
moving loads that pass over them, of course the curve cannot be 
equally loaded in all places; and it is, therefore, improper for the 
formation of an arch unless some means are resorted to for render- 
ing the figure immutable. Now, if we suppose that the chain 
instead of being made of moveable links should be composed of a 
series of blocks strung upon a cord, and so shaped that the sides 
which come into contact with each other shall be flat planes 
bisecting the angle that the cord would make at each joint, in 
that case we should produce an arch or curve of some stability, 
or one that would bear a little change of form without tumbling 
down, for the equilibrium of the original festoon obtained only at 
the points of contact, where the pressures were perpendicular to 
the touching surfaces which may be considered as infinitely small. 
Therefore, if the curve or sustaining line still passes through the 
touching surfaces perpendicularly, and we conceive those surfaces 
extended, the conditions that are required for equilibrium still 
obtain with this difference that we obtain an approximation to the 
stability of a body resting on a horizontal plane. If the perpen- 
dicular through the centre of gravity falls within the base of the 



644 OF ARCHES. 

body, it will not only stand, but will require some force to push 
it over. 

1158. These conclusions obviously deducible from the princi- 
ples of the festoon, shew that the longer the meeting joints are, 
and the greater will be the stability of the arch, or that it will 
require a greater force to break it down. Therefore it is of the 
greatest importance to have the arch stones as long as economy 
will permit. This principle appears to have been known to the 
older builders, who, with ^ view to obtain this auxiliary of strength 
without a profuse waste of material, made some of the rings of 
stone that composed their arches to project from six inches to a 
foot below the general face of the work, in the form of ribs, which 
are frequently found in gothic arches, apparently as if introduced 
for the sake of ornament alone, but which were no doubt meant 
to assist in supporting the work from the stiffness and stability 
they give to it. 

1159. Such being the general principles upon which the form 
of the festoon arch depends, we will now proceed to explain how 
this curve, which is called the catenarian arch, may be obtained, 
and will remain in equilibrio when the weight of a road way is 
placed upon it. 

Suppose it should be required to ascertain the form of an arch 
of thi§ description, which shall have the span A B, and height 
F S, Fig. 268, and which shall have a road over it, the height 
and slopes of which shall correspond with the curved line C 
D E above it. Let the whole figure A C D E B be inverted so 
as to form a figure A c c?e B. Let a chain of small brass wire, or 
any material of uniform weight and thickness, be suspended from 
the tv/o points A and B, and let it be of such a length that its 
lowest point shall hang at, or rather below/, corresponding to F. 
Divide A B into any number of equal parts 1, 2, 3, 4, &c., and 
draw vertical lines cutting the chain in the corresponding points 
1, 2, 3, 4, &c. Now take pieces of another chain of the same 
size, and hang them on at the points 1, 2, 3, &c. of the chain 
A/ B, and this will alter the form of the curve. Cut or trim these 
pieces of chain till their lower ends all coincide with the inverted 
road-way c d e. The greater lengths that are hung near the ends 
A and B, will pull down these points of the chain, and cause the 
middle point/ (which is less loaded) to rise a little and will bring 
it near its proper height. 

It is plain that this process will produce an arch that is in a 
perfect state of equilibration in all its parts, under a load of homo- 
geneous matter placed upon it, because the length of chain being 
various, will be in proportion to the weight of soil at correspond- 
ing positions, but some further considerations are necessary for 
making it exactly suit our purpose. It is an arch of equilibration 



THE CATENARIAN ARCH. 645 

for a bridge that is so loaded that the weight of the arch stones is 
to the weight of the matter with which the haunches and crown 
are loaded, as the weight of the chain A/ B is to the sum of the 
weights of all the small pieces of chain hung to it, or very nearly 
so. But this proportion is not known beforehand; we must there- 
fore proceed in the following manner: Adapt to the curve pro- 
duced in this way, a thickness of arch stones as great as may be 
thought sufficient to insure stability; then compute the weight of 
such arch stones, and the weight of the earth and gravel with 
which the haunches are to be filled up and the roadway made; 
and if the proportion of these two weights be the same with the 
proportion of the weight of chain, we may rest satisfied with the 
curve now found; but if different, we must calculate how much 
must be added equally to, or taken from each appended piece of 
chain, in order to make the two proportions equal. Having alter- 
ed the appended pieces accordingly, we shall get a new curve, 
which may perhaps require a little trimming of the bits of chain 
to make them fit the roadway, and the curve so obtained will be 
infinitely near to the curve required. 

1160. Professor Robison tried this method experimentally on a 
large scale, the arch having a span or opening of 60 feet, and a 
rise or height of 21 feet, the arch stones of which were only 2 
feet 9 inches long, and the arch loaded with rubble stone and 
gravel. A previous computation was made on the supposition 
that the arch was to be nearly elliptical. The distance between 
the points 1, 2, 3, &c. were adjusted so as to determine the pro- 
portion of the weights of chain agreeable to the supposition. The 
curve differed considerably from an ellipse, making considerable 
angles with the verticals at the spring of the arch. The real 
proportion of the weights of chain, when all was trimmed so as to 
suit the roadway, was very different from what was expected. It 
was adjusted, and this made very little change in the curve, and 
it was found that it would not have changed it two inches in any 
part of the real arch. When the process was completed, he con- 
structed the same curve mathematically, and found that it did 
not differ sensibly from the mechanical construction. This result 
was highly satisfactory, since it showed that the first curve formed 
by about two hours labour, on a supposition considerably different 
from the truth, would have been sufficiently exact for the pur- 
pose, since it did not vary in any place three inches from the ac- 
curate curve, and was, therefore, far within the joints of the in- 
tended arch stones. Therefore this process which any intelligent 
workman, though ignorant of mathematical science may go 
through with little trouble, will give a very proper form for an 
arch subject to any conditions. 



646 OF ARCHES. 

1161. The chief defect of the curve found in this way is a 
want of elegance, because it does not spring at right angles to the 
horizontal line, but this is the case with all curves of equilibration, 
as well as with segments of circles, and is of no consequence as to 
its strength, because in the immediate vicinity of the piers or 
abutments any form we please may be given to the curve, be- 
cause the masonry is always solid in these places, and such a de- 
viation from the curve of equilibration at its springings as will 
add to its strength by making it rise perpendicularly is even pro- 
per. The construction of that curve supposes that the pressure 
on every part of the arch is vertical; but gravel earth and rub- 
bish always exert a degree of lateral pressure in the act of set- 
tling and retain it afterwards, and this will require a little more 
curvature at the haunches of the arch to balance it. What the 
extent of this lateral pressure may be, cannot be deduced with 
confidence from any experiments yet made, and to provide against 
it, it would perhaps be more proper to divide the chain itself into 
the equal parts 12 3, &c., instead of the horizontal line A B, for 
then the curve would approach nearer to its proper form. 

1162. The Festoon or catenarian arch has not been much used, 
which is likewise the case with the Parabola, the Hyperbola and 
Cycloidal curves, as none of these appear to offer any advantages 
greater than what can be obtained from the circle or ellipse, and 
accordingly the semicircle, or lesser segment of a circle, and the 
semiellipse are the forms constantly used in bridge building, not 
only because they are more easily set out and built, and are liable 
to fewer errors of construction, but because it is thought they 
produce a more pleasing or beautiful appearance. The choice 
of the curve must be in a great measure governed by the forma- 
tion and nature of the place in which the bridge has to be built; 
keeping in mind, at the same time, that the semicircular arch is, 
under most circumstances, the strongest, and produces the least 
expansion or lateral pressure on its foundations. If a river runs 
in a deep valley, below the level of the adjacent country, and the 
roads or approaches to an intended bridge are considerably above 
the water, then of course a semicircular arch, or even such an 
arch elevated upon piers of such height as will prevent any de- 
pression in the road at the bridge, would be preferred. But if 
the country is level and very httle elevated above the surface of 
the river, a semicircle of wide span would produce a considera- 
ble hill to be surmounted; to obviate which, an elliptic arch, or 
a segment of small rise must be adopted; or the breadth of the 
river must be divided into a number of arches, which renders the 
construction more expensive, and may often produce an incon- 
venient obstacle to the flowing of the' water. These considera- 



FORMS ANP PARTS OF ARCHES. 647 

tions must be again influenced by the nature of the river. Should 
it be navigable, small arches are objectionable, and, if its vessels 
are masted, a high or semicircular arch may become necessary, 
notwithstanding the elevation of the road would render it objec- 
tionable. Again, if the river is subject to great and rapid floods 
or freshets, flat or low arches are very objectionable, unless they 
are so elevated upon piers as to place them above the greatest 
height the water can reach; for few accidents occur to bridges 
from the action of the stream against their piers, but they are 
washed away by the water rising so high that it cannot find vent 
through the arches, and therefore exerts its force in lateral pres- 
sure against the bridge itself. The elliptic arch not only has the 
advantage of admitting a low and level road, but a more import- 
ant one, which is the small quantity of material it requires for 
its construction, the difference in quantity of masonry being as 
the radius of the circular arch is to the semiconjugate diameter 
of the ellipse which can be inscribed in it. Thus, for example, 
suppose an arch of 72 feet span is required. To make this a 
semicircle its radius and consequent height must be 36 feet. But 
if an elliptic arch rising 24 feet should be selected, 24 feet the 
semiconjugate diameter, is but two-thirds of 36 feet, consequently 
not only one-third of the cost of materials and labour will be 
saved by adopting such an arch, but the piers or abutments will 
be relieved from the same proportion of weight. 

1163. In addition to the local circumstances above mentioned, 
which will influence the form of arch, its stability and pressure 
must also be taken into consideration, and as the several compo- 
nent parts of an arch and bridge have technical names appro- 
priated to them, these must be previously explained, together 
with a few principles of the construction of arches that have not 
yet been referred to. 

One of the first and most essential rules of construction is, that 
when an arch is composed of a number of separate blocks of stone 
or other material placed in contact with each other, the joints 
must be as flat and true as possible to insure entire and perfect 
contact; and all those joints must be perpendicular to the curve, 
(or to tangents to it at their point of contact,) which forms the 
inside of the arch. Of course, therefore, these joints must diverge 
or open as they recede from the water, consequently all the 
blocks that form an arch must be wedge-shaped, and all such 
blocks are called voussoirs. The under side of every arch is called 
its intrados or soffit; the former word being used when large 
arches, like those of bridges, are spoken of, and the latter for small 
arches, such as usually occur in buildings. The outside of an 
arch is in like manner called its extrados or hack. Another hue 



648 OF ARCHES. 

frequently parallel to this last is called the archivolt. It is the 
curve formed by the upper sides of the voussoirs or arch stones, 
and is parallel to the intrados when all the voussoirs are of equal 
length, otherwise it cannot be so. By the archivolt is also some- 
times understood the whole of the voussoirs. The two lowest 
extremities of an arch are called its springings or springing lines, 
and these, like the voussoir joints must lie in directions perpen- 
dicular to the intrados, consequently all semicircular or elliptic 
arches will spring from horizontal surfaces, being parts of the 
diameter of the arch or ellipse. All segments of circles will 
spring from lines that are parts of radii of such arches, and all 
elliptic segments or other curves will spring from lines varying in 
their horizontal angles according to the extent of the segment 
taken, because such lines must be perpendicular to the part of 
the curve they intersect. 

1164. In order to give an arch a firm seat or foundation upon 
its pier or abutment, they must therefore be finished at their tops 
in accordance with the directions of the springing lines. Piers for 
semicircles or semiellipses therefore finish with flat tops of large 
stone called cushions, while those for every other kind of arch 
must terminate in stones cut to the angles of the springing lines, 
and such stones, which are always selected of the largest and best 
kinds, when so finished are called skew backs. This, in some mea- 
sure, influences the width of the piers, because when two arches 
spring from the same pier, a double skew back will be necessary, 
or one presenting an equal angle to each arch. We may consi- 
der such double skew back as composed of two right angles, hav- 
ing one perpendicular side (over the centre of the pier) common 
to them both; the flat top of the pier will then be their common 
or continued base, and the sloping faces will be their hypothe- 
neuses. Now the sloping face or hypotheneuse must always be 
equal to the height of the voussoir that is to lie upon it, which 
determines the length of one side of the triangle, and as that is 
right angled, of course the height of the perpendicular and the 
base are also determined; and twice the length of the base will be 
the least width for a pier that two such arches can spring from, 
even when the arches are in contact with each other; but when 
they are distant, the quantity of their distance must be added to 
the width. So likewise a semiarch requires the width of its pier 
to be equal to twice the length of the voussoirs used to form the 
arch. The central voussoir of every arch is called its key stone, 
for reasons that will hereafter appear, and this stone is generally 
larger than the others that compose the arch. The angular sur- 
face between one arch and another is called a spandrelL The 
centre of an arch is called its crowti, and a certain distance up 



EQUILIBRIUM AND STABILITY OF ARCHES. 649 

each side, from the springing lines, its haunches, but their extent 
has never been accurately defined. The face of an arch is the 
termination that is presented at the sides of a bridge. 

1165. The stability, strength, and pressure of arches have 
been differently treated and considered by different builders, 
authors, and mathematicians, and no subject has perhaps engaged 
more particular attention than this has done. Theorists have, in 
general, taken up and supported the arch of equilibration, as 
being superior to all others in its qualifications. But practical 
men, without denying, or attempting to dispute the truth and ac- 
curacy of the deductions that have been made, rest their security 
more upon positive strength than on nicety of balance or equili- 
bration, and in so doing they have the sanction of some of the 
most able theorists and mathematicians. By an arch of equilibra- 
tion is meant an arch composed of blocks of stone or any other 
materials, the weights and lateral pressures of which have been 
so exactly determined and calculated, that if they should be put 
together with smooth or actually polished joints, without any mor- 
tar or cementing matter, the arch would have no tendency to fall 
or even change its figure, and indeed could not do so without some 
extraneous force, because the pressures of all the blocks, (produced 
by the joint action of their weight, and lateral thrust,) are in a 
state of perfect equality or equilibration in every part of the arch. 
There can be no doubt but that such a state of universal equili- 
brium is highly desirable in every arch, and therefore ought 
to be sought for, as far as possible; but its perfect existence is 
almost incompatible with the nature of materials, as well as 
w^orkmanship, and may sometimes interfere with the beauty 
of the design, or object of the designer. Thus the voussoirs 
that are shown surrounding the centring in Fig. 253, are all of 
one size; consequently this cannot be an arch of equilibration, for 
the five stones in the centre will have a tendency to fall, only 
equal to their weight, having nothing else to support, and in their 
tendency to descend, will produce lateral or thrusting pressure, 
which will be transferred to the lower stones on each side of them. 
The five next lower stones on each side have very little more to 
support them than the stones in the crown; they will therefore 
have an equal tendency to descend, augmented by the weight of 
the stones in the crown which they support, together with the 
lateral pressure of those stones; consequently the lower stones are 
more loaded than the upper ones, and will be acted upon by a 
greater force to throw them out of their positions. To make such 
an arch an arch of equilibration we must therefore lighten and 
diminish the size of the stones in the crown, while we augment 
the size and surfaces of those below. For in arches, the pressure 
82 



650 OF ARCHES. 

(compounded of the weight of the materials, and their tendency to 
thrust or extension) augments from near the crown towards the 
springings; consequently the quantity and weight of material must 
increase in a similar ratio. In the new London bridge, part of 
which is shown by Fig. 255, something like this is attempted, and 
the voussoirs over the crown are shorter than those lower down, 
and it occurs in many other bridges, particularly in the magnifi- 
cent cast iron arches of the Southward Bridge, the centre arch of 
which spans 240 feet, and is therefore the largest arch in the 
world; at the same time that it is one of the flattest, since this 
enormous arch has a rise or versed sine of only 24 feet. The two 
side arches span 210 feet each, with a rise of 18 feet, and the 
main rib of cast iron, which forms the lowest member of these 
arches, is 6 feet high in the crown and increases to the width of 
8 feet at the springing lines. 

1166. The equilibrium of the variouspartsofan arch would be 
a matter of first rate importance, provided a large arch had to 
stand quite alone and independent of every other object, and was 
not subject to any change in the quantity or direction of the load 
pressing upon it; and if this was the case, there could not perhaps 
be a better method of determining the form of an arch and the 
roadway to pass over it, than that already given with the chain 
and appended pieces. (1159.) There is, however, a want of ac- 
cordance between the exact vertical direction in which the pieces 
of appended chain will pull upon the drooping chain, and that in 
which the earth or other materials necessary to form the road- 
way press upon an arch. For earth and other materials, par- 
ticularly if rain soaks into them, will not only press perpendicu- 
larly, but will exert a kind of hydrostatic or lateral pressure; and 
again, the load that comes upon a bridge is not uniformly diffused 
over the whole arch at once, but is progressive. It commences 
its operation by pressing down one of the haunches, while there 
is nothing to counterbalance it on the other side, it then comes 
over the crown and goes over the next haunch; hence the pieces 
of appended chain which are constant and equable in their strain, 
may nearly represent the action of the earth upon the arch, but 
are by no means a fair representation of the action of a moving 
load, which we are now supposing to be so great as to be capable 
of producing a sensible action upon the arch. 

1167. The student will derive important information as to the 
nature of these pressures, and what takes place in an arch, as 
well as in the means of preserving its figure, by the simple expe- 
dient of bending a piece of cane or other flexible wood of 18 or 
20 inches long, into the form of a semicircular arch, and securing 
it in that position by inserting its two ends into holes bored in a 



EQUILIBRIUM AND STABILITY OP ARCHES. 651 

piece of flat board to receive them. If we press on one side of 
the arch so formed, the crown will descend, and the opposite 
haunch will swell or extend outwards, thus rendering the stick an 
irregular curve. Again, if we press upon the crown that will 
sink, but in doing so will extend or swell out both the haunches 
at once, so as to give the cane something like a semi-elliptic form, 
and it will be found that a very small force exerted, will produce 
these effects, thus showing that the cane arch can only sustain a 
small load that presses unequally upon it. Having tried this ex- 
periment, bore a few holes through the board in the line of the 
cane and near the centre of the arch, and having passed some 
strings through them, tye one string to the crown, and let the 
others radiate and be tied to the cane at equal distances on each 
side of the crown or centre, and let all the strings be then strain- 
ed and tightly fixed in their holes in the board in such manner 
that the semicircular form of the cane may not be disturbea, and 
it will be found that the strength of the arch will be much in- 
creased; for now if we bear upon its crown the haunches cannot 
swell out, being restrained or kept in their positions by the strings; 
and in like manner if the pressure is made over one haunch, the 
other cannot rise for the same reason. This points out very 
clearly what must be done to give stability to a real arch. In the 
first place the ring or hollow half cylinder of masonry that forms 
the arch, must be of such strength and thickness as will prevent 
its crushing by the load we require to put upon it, and then that 
arch must be so tied down as to prevent the possibility of any 
casual load that may come upon it distorting or disturbing its 
figure. 

This tying down cannot be accomplished by strings, as in the 
model, nor even by chains or iron bars, because they would im- 
pede the navigation, and there would be no effectual way of 
securing their bottoms. But weights applied upon the top of the 
arch, will produce exactly the same effect as strings or ties ap- 
plied beneath it, and thus the very earth or other solid material 
that is applied to cover the arch, and to fill in the spaces or 
spandrells between one arch and another instead of oppressing, 
gives strength to the arch and enables it to bear unequal loads; 
for the heaviest wagon that can arrive on the crown of an arch, 
will weigh nothing in comparison to the weight of the quantity of 
materials that has been filled in between the spandrells; and as 
all this quantity of earth has to be raised before the two haunches 
can possibly expand, so of course, as that cannot be effected the 
arch will be stable. 

1168. This mode of proceeding, though it may appear sound in 
principle, is not so, and could not be applied to practice without 



652 OP ARCHES. 

very nice adjustment, or some modification. Because notwith- 
standing loading the haunches will effectually prevent them swell- 
ing out in obedience to the power of a weight applied at the 
crown, still from the very form of the arch very little or no soil 
will be necessary upon its crown, while a very large quantity 
will be required over the haunches to fill in the spandrells and 
form a level road. The pressure of the earth will not therefore 
imitate this action of the strings in our model, for while we have 
two immense loads at the sides over the haunches, the crown or 
central tie is deficient, and we have nothing to counteract them; 
consequently the crown of the arch will rise in obedience to their 
pressure, by which the symmetry of the curve will be destroyed, 
and with it probably the whole arch. One of two things must 
therefore be done. Either the crown itself must be loaded until 
it is capable of balancing the pressure of the haunches; or, if the 
crown is not weighted, then the haunches must also be kept free 
from that quantity of load which would be prejudicial to the 
crown. An instance of the necessity of attending to this species 
of equilibrium occurred in Wales in the building of a bridge over 
the river Taff near Llantrissent, in Glamorganshire, known in 
the country by the name of the Poni y ty Prydd, and which is con- 
sidered one of the most extraordinary bridges in Great Britain, 
while it is interesting on account of the history of its construction. 
The Taff, though by no means a wide river, runs between two 
rocks, and is in such a mountainous district that it is subject to 
great and rapid floods, and the first stone bridge erected across it 
consisted of three light and elegant arches, built in the valley by 
a Mr. William Edwards, an uneducated mason of the country, 
and was finished in 1746. It was much admired and gave general 
satisfaction, and Edwards was himself so satisfied with the stabili- 
ty of his work that he gave security for its standing seven years 
without needing repair; but in about two years and a half after 
its erection, a very heavy flood came on, bringing many trees, 
branches and other objects down the stream, and as these were 
stopped by the bridge, they formed a dam which impeded the 
water, and this rose to such a head as to wash the whole bridge 
away. Of course Edwards was compelled to erect another bridge; 
and he proceeded on his duty with all possible speed. Being de- 
termined on this occasion to make his work secure, he adopted a 
single arch, which was a segment of a circle the diameter of 
which was 170 feet The span or chord of the arch was 140 
feet, and in order to place it completely out of the reach and 
danger of all floods, he raised it 35 feet above the water. The 
rocky sides gave him excellent foundations or abutments for such 
an arch, and he had no difficulty in carrying it over from one 



EQUILIBRIUM AND STABILITY OP ARCHES. 653 

rock to the other. All that now remained to be done was build- 
ing the side walls and filling in soil over the haunches to procure 
a level road. This work proceeded and was nearly finished, 
when the soil placed upon the haunches, without an equivalent 
balance on the crown, proved too much for them, for they sunk, 
pushing the crown upwards so as to force the stones out of their 
positions, and in 1751, just when this second bridge was on the 
eve of completion, it was thus wholly precipitated into the water 
below. 

Such a succession of misfortune would have disheartened most 
men, but it had not that effect on Edwards. He saw the error of 
his proceeding, and was fully aware of the cause of his bridge 
failing; and believing that there was no better and eflfectual way 
of making a bridge than the one he had attempted, he began his 
work again, and rebuilt an arch similar in every respect to the 
one that had fallen down; but instead of overloading the haunches 
as he had done before, the happy idea of introducing hollow brick 
tubes or culverts across his bridge occurred to him, and he ac- 
cordingly built three of these in each spandrell, making the lowest 
nine feet, the middle ones six feet, and the inner ones three feet in 
diameter. These ran horizontally from one side of the bridge to 
the other, and formed six cylindrical holes or passages through it. 
Earth was of course rammed into the spandrells, under, around 
and above these culverts for the purpose of supporting them, and 
raising the road to its proper level; but the smaller weight of 
earth required in consequence of the span occupied by the hollow 
tubes or culverts, completely answered the purpose, and this third 
bridge, which was finished in 1755, is still standing a monument 
of the perseverance and ingenuity of its constructor, and is uni- 
versally admired for its stability combined with its lofty, light, 
and elegant appearance. 

1169. We perceive, therefore, that it would not be safe to 
construct the arches of a bridge of equal sized voussoirs, or even 
such a one as would be in a state of equilibrium with respect to 
itself; and then to fill in the spandrells or spaces between that 
and other arches with soil thrown in at random; for the quantity 
of soil necessary over the commencement and haunches of the 
arch is always so much greater than what can be placed upon 
the crown, that the greater load would overpower the lesser one, 
and by protruding the crown would cause the destruction of the 
arch. Some mode of securing the arch must therefore be sought, 
and such a one will be obtained by giving its two lower sides 
longer and more extended voussoirs; an expedient that brings the 
arch nearer to one of equilibration, and which may or may not 
interfere with the appearance of the external design. If it is 



654 OF ARCHES. 

desired that the appearance of the arch should be such as to pre- 
sent voussoirs of equal size, it will only be necessary to cut the 
end or face voussoirs that present themselves to view accordingly, 
and the side walls may be built upon them, notwithstanding the 
hidden voussoirs within the arch (and which bear more of the 
load than the exterior ones,) may have any length we choose to 
give them. In Westminster Bridge, London, every alternate 
voussoir has the appearance of being twice as deep or high as the 
intermediate ones; but it must not, on this account, be supposed 
that the bridge is so built. It is merely an appearance that is 
produced by cutting the external or facing stones in such manner 
as to produce this effect for architectural beauty alone. In 
Blackfriar's bridge the voussoirs are, with a similar object, made 
to appear all of one size, or the extrados and intrados are paral- 
lel, and each alternate stone seems entire and the intermediate 
ones in two pieces with a rusticated joint between them, while in 
fact the voussoirs next the key-stone of the centre arch are each 
six feet seven inches long, and each stone in succession gets longer 
as they proceed to the springing stones, which are between eight 
and nine feet long. This is the true principle for constructing a 
large arch; for if every voussoir as it recedes from the centre is 
made longer than the preceding one, the arch becomes so strong 
at its haunches that no load of earth that is necessarily placed 
upon it can derange it, besides which the spaces to be filled up 
with soil are greatly diminished by the stone that gives strength 
to the arch. Neither is it necessary that these large voussoirs 
should be all in one piece, for if that was the case, there would 
be difficulty in getting large stones in sufficient quantity. Large 
stones are always selected for the ring or face of the arch, as 
well as for its intrados; but within the arch, smaller stones may 
be used, provided they are as hard and incompressible as the rest, 
and that their points are made to radiate and coincide exactly 
with the directions of the joints of the larger stones. In West- 
minster bridge this principle was carried to such an extent that 
the voussoirs of the arches were carried out and extended until 
they met or intersected the perpendicular solid masonry of the 
piers, as shown at Fig. 269, so that no change of form could take 
place without first producing a compression of the pier; and in 
Blackfriars bridge, Mr. Mylne very ingeniously connected all the 
arches together from one end of the bridge to the other by caus- 
ing a part of the weight of every pair of adjacent arches to rest 
upon an inverted arch that was constructed in the piers to re- 
ceive them. 

1170. It thus appears that the precise equilibrium of the arch 
itself, the necessity of which has been so strongly insisted on, 



EQUILIBRIUM AND STABILITY OF ARCHES. 655 

and so largely written upon by several mathematicians of the 
highest eminence, is of little practical importance. The two 
authors now most relied upon on these subjects, are the late Pro- 
fessors Robison of Edinburgh, and Hutton of Woolwich. The last 
being author of the well known course of mathematics. The 
former wrote a new and original treatise of considerable length 
on the mathematical principles of arches and domes, for the sup- 
plement to the third edition of the Encyclopedia Britannica, and 
which has been embodied in the subsequent editions of that work; 
and the latter had great practical experience on the subject, 
combined with his mathematic knowledge, having been first 
brought into public notice by a report and scientific investigation 
that he made and published upon the cause of the failure and 
falling of the bridge at Newcastle, upon the river Tyne, in 1771, 
and having been afterwards constantly called upon professionally 
for advice in most of the difficult cases of bridge construction in 
England, for nearly half a century after that period. And he has, 
moreover, published a treatise on the principles of bridges which is 
justly admired and often consulted. Neither of these authors pay 
any regard to the principle of equihbrium, and Robison after 
describing the nature of the equilibrium of arches even goes so far 
as to say,* *'Thus much will serve we hope to give the reader a 
clear notion of this celebrated theory of the equilibrium of arches, 
one of the most delicate and important applications of mathe- 
matical science. Volumes have been written on the subject, and 
it still occupies the attention of mechanicians. But we beg leave 
to say, with great deference to the eminent persons who have 
prosecuted this theory, that their speculations have been of 
little service, and are little attended to by the practitioner. Nay, 
we may add, that Sir Christopher Wren, perhaps the most ac- 
complished architect that Europe has seen, seemed to have thought 
it of little value, since among the fragments of his writings that 
have been preserved, he takes no notice of it, and considers the 
balance of arches in quite another way." A few lines afterwards 
Professor Robison observes, ''The general facts which occur in 
old arches are highly instructive, and deserve the most careful 
attention of the Engineer; for it is in this state that their defects, 
and the process of nature in their destruction are most distinctly 
seen. We venture to affirm, that a very great majority of these 
facts are irreconcileable to the theory." 

1171. The principle adopted by Robison and Hutton, for deter- 
mining the strength and pressure of arches, is the same as that 
applied to determining the lateral thrust of beams in carpentry 

* Robison's System of Mechanical Philosophy, Vol. I., p. 634. 



656 OP ARCHES. 

(957) in which each stone is supposed to possess sufficient cohesion 
or strength to enable it to preserve its form or figure against the 
action of its own weight, and any lateral pressures to which it 
may become subject, and a right line supposed to pass through 
each stone in the direction in which the pressure is exerted, may 
be called the axis of pressure. Such lines will be straight through 
each perpendicular stone, but will make angles with each other 
in adjacent stones, and of course such lines can be made use of as 
two sides of a parallelogram of forces for determining the resultant 
of their oblique action upon each other; consequently, if the cohe- 
sive strength of the stone, its weight, and that of the earth or 
other load to be put upon it, and the directions of the axis of 
pressure are known, these data will be sufficient for determining 
the thickness that must be given to an arch to enable it to bear 
a given load. 

1172. It thus appears that there are three distinct ways in 
which the formation of arches may be viewed and considered, and 
these are summed up in nearly the following terms in the general 
scholium with which Dr. Hutton concludes the second section of 
his excellent little treatise on bridges. The first method is that 
which is derived from the consideration of the equilibrium pro- 
duced by the mutual thrusts, weights and pressures of the arch 
stones, supposing them prevented from sliding on each other at 
the oblique joints, either by their roughness and friction, or by the 
cement joggles, dowells, or iron clamps let into every adjacent pair 
of stones, which give the arch the effect of one compacted frame, 
pressed on vertically by the weight of the superincumbent walls 
and load above it, and which seems to be the true and genuine 
way of considering the action of a load upon an arch. 

The second method is the arch of perfect equilibration or ba- 
lanced arch, computed on the supposition that the arch stones 
have their butting surfaces perfectly smooth, and at liberty to 
slide on each other. But Dr. Hutton observes this is little insist- 
ed on, because it is founded on suppositions which cannot exist in 
nature or art, and which consequently can never occur in the 
real construction of an arch. 

The third method has for its principle the catenarian curve or 
festoon reversed, which is a strictly just and useful principle. 
This idea, when first proposed by Dr. Hooke, and afterwards treat- 
ed upon by De la Hire in his Traite de JlfecaTii^'we, went no further 
than balancing a single or thin arch formed by voussoirs only, with- 
out any wall to fill up the flanks, and was therefore hardly appli- 
cable to practical purposes. But this same principle as extended 
hy Professor Robison, by appending chains and making their 
weight proportionate to the load as before described (1159-60) 



EQUILIBRIUM AND STABILITY OF ARCHES. 657 

is SO just and so easy in its practical operation, as to have render- 
ed it useful and available. The equilibrium that any theory 
establishes, must, however, always be of a delicate nature, because 
it supposes the parts to touch only in single points, and may, 
therefore, be called a tottering equilibrium, since any other weight 
or force added at any one part, would press the arch out of its 
true balanced form, by shifting the points of contact. This is, 
however, prevented by giving considerable length to the voussoirs, 
by which stability is insured, because the altered figure will then 
Jfind new points to bear upon, and hence, the longer the butting 
joints of the arch stones are, and the more stable and secure the 
whole fabric will be. 

1 173. As to the materials to be selected for building arches 
little can be said in addition to what has been before observed, 
since it will from thence be inferred, that large masses are to be 
preferred to small ones, on account of the larger surfaces they ex- 
pose to each other; and as the force brought into action in an arch 
is one of compression, of course the hardest and least elastic mate- 
rials are the best, while soft sand-stone or badly burnt bricks are 
among the worst things that can be used. A long tunnel which 
was cut through a considerable hill in the vicinity of London, with 
the view of obtaining a level main road, and called the Highgate 
Tunnel, failed entirely from one end to the other, and all fell in 
in a single night, within a week after the final completion of the 
work, owing to the bricks, of which the arch was formed, not 
being sufficiently hard to resist the pressure of the great load of 
earth that was above them. Timber is an objectionable material 
for forming arches, unless extraordinary care is taken to ventilate 
the abutments and preserve them from humidity, otherwise it will 
rot in these places, and the arch must sink or fall. Stone, from 
the magnitude of the blocks in which it can be obtained, is there- 
fore decidedly the best and most durable material for large arches; 
and well burnt hard bricks properly disposed may be considered 
as the next best. Cast iron also appears to be a very excellent 
material, because the castings can be so arranged and put 
together with screw bolts, wedges, keys, and dovetails, that hollow 
or skeleton voussoirs may be formed with diagonal braces within 
them, so as to obtain all the strength of stone, with very exten- 
sive joining surfaces, and yet with a comparatively small weight 
of metal. Cast iron, when properly formed and disposed, will 
withstand an enormous force of compression, and the only doubts 
as to the propriety of its use arose from its liability to oxydation 
and consequent decay, and from its expansion and contraction 
with change of temperature, Metals when heated and cooled ex- 
pand and contract with a force that is almost irresistible, (663,) 
83 



658 OF ARCHES. 

and as a large arch must expose a very long and continuous sur- 
face to the action of the atmosphere, it was feared that an arch 
built of iron might expand and elongate, in hot summer weather, 
to such an extent as to push out its abutments, or cause its crowii 
to rise, should they have strength enough to resist this motion; and 
that in winter, the arch would sink from the contraction of the 
parts, thus producing a constant motion in the joints which it was 
feared might fret and break them, and thus endanger the stability 
of the work. The experiment has, however, been tried on a suffi- 
ciently large scale to show that these fears are groundless; and 
that a perfectly stable arch may be constructed if properly 
managed and attended to. The oxydation is effectually prevented 
by keeping the iron well painted in its joints with earthy oil co- 
lours (675) and the effects of expansion and contraction are met 
by tying the pieces that compose the voussoirs firmly together 
transversely but not longitudinally. The voussoirs are connected 
with each other by dowells, or tenons and mortices, and are pre- 
vented sliding over each other or changing their positions by 
wrought iron keys or screw bolts, which are not drawn quite tight, 
because the play necessary in each joint will be very small, 
although the sum of all their actions may be considerable. 

1174. The first bridge wholly of cast iron (with the exception 
of the connecting bolts and keys of wrought iron) that was ever 
attempted was placed over the river Severn, at Colebrooke Dale, 
in Shropshire, England, in 1779, by Mr. Abraham Darby, an iron 
master of that place. It is a single semicircular arch of 100 feet 
6 inches span, and contains 378J tons of iron. The roadway is 
24 feet wide, and is supported by five parallel ribs, each rib con- 
sisting of three concentric circles, connected together by radiating 
pieces. The lowest ring of each rib is a complete semicircle; the 
others are only segments, being terminated or cut off by the road- 
way. The roadway is covered with cast iron plates, and has an 
iron railing on each side. It stands upon iron foundation plates 
let into a solid but stratified rock. There is little of science in 
the construction of this bridge, if we except the enormous magni- 
tude of the castings, as each inner circle of the rib is in two 
pieces only, each 78 feet in length. From the simplicity of its 
construction it was put together and finished in three months, and 
as it stands between two solid rocks the road leading to it is made 
■up on each side by solid masonry. 

1175. The next large iron bridge that was erected in England 
was over the river Wear at Sunderland, Durham. It was began 
in 1793 and finished in 1796. The stone abutments are 70 feet 
high above the ordinary surface of low water to the springing of 
the arch. The iron arch has a span of 2S6 feet, and is a segment 



OP IRON BRIDGES. 659 

of a circle 444 feet in diameter, having a rise or versed sine of 34 
(eet with its soffit 100 feet above the Jov^^ water Hne of the har- 
bour, therefore vessels with high masts can sail under it. The 
road over this bridge is 32 feet wide, with iron railings on each 
side. The bridge consists of six ribs, which are formed on a very 
different principle to those last described, for instead of working 
with pieces of iron of from 50 to 70 feet in length, each rib is here 
composed of no less than 125 small frames or skeleton voussoirs, 
each about two feet wide in the length or curve of the rib, and 
five feet deep in the direction of the radius. These hollow blocks, 
or voussoirs, are held together by wrought iron bars fitting into 
grooves, and hollow pipes of cast iron with flanches, having screw 
bolts passing through them, connect the ribs together. The 
framing thus forming the arch, is the sole support of the bridge, 
but to render the roadway (which is formed of timber covered 
with tar and lime and afterwards with marl) more flat, perpen- 
dicular posts of iron rise from the top of each rib and reach to the 
underside of the strong timber joists which are laid over each rib 
in the lengthwise direction of the bridge, their distance asunder 
diminishing towards the crown and being regulated by the diame- 
ter of a cast iron ring, which is introduced between each post, of 
such diameter that while the bottom of the ring rests on the top 
of the rib, its top may reach to and support the bottom of the tim- 
ber joists, and the vertical iron posts are in contact with the two 
sides of each ring to prevent their flattening by pressure. This 
bridge contains only 260 tons of iron, of which 214 are cast and 46 
wrought iron for fixing the parts together; and its cost was 
^27,000, including the immense abutments of almost solid mason- 
ry, 24 feet thick by 42 feet broad at the bottom, diminishing to 37 
feet at the top. It has been much admired for its light and ele- 
gant appearance, and is justly esteemed a bold effort of art, and 
an incontrovertible evidence of what may be accomplished in cast 
iron, but still its principles are not good; 1st. because its frames 
are much too short, thereby multiplying the number of joints very 
unnecessarily, while the pieces that compose the frames are of 
unequal dimensions, which is also improper; 2ndly. the preserva- 
tion of the due position of the frames is made to depend too much 
upon wrought iron bars and bolts, which should be as much as 
possible excluded from structures of this kind; 3dly. circles in the 
spandrells are not a good and effectual support for the roadway, 
because a circle is not a strong figure unless it is equally compress- 
ed on every part of its circumference, which is not the case in this 
bridge. For circles, disposed as in this structure, act rather as 
springs than as solid supporters to the road. 

1176. The boldest conception that has ever been formed for 



660 OP IRON BRIDGES. 

constructing an iron arch was that of Messrs. Telford and Dou- 
glas, for building a bridge over the river Thames at London, in a 
single arch of cast iron, which was proposed to be a segment of a 
circle of 1450 feet in diameter, having a span or opening of 600 
feet, and a rise or versed tier of 65 feet. The bridge was to con- 
sist of seven ribs, having a roadway upon them of 45 feet in 
width at the crown or centre, increasing in each direction until it 
should be 90 feet wide at each end. The design for this bridge, 
which was truly elegant, was submitted to the British Parliament 
with the estimate for its construction in 1801, and for some time 
serious thoughts were entertained of carrying it into execution. 
It was computed to require about 6500 tons of iron with 432,000 
cubic feet of granite, and 20,029 cubic feet of brick-work for its 
abutments, and its total cost was to be ^262,289. The possibility 
of its being put up so as to be a permanent erection, and its ad- 
vantages and disadvantages were submitted to most of the emi- 
nent Engineers and mathematicians of England, who concurred 
in the possibility of its execution and stability; but after due deli- 
beration in parliament it was thought too bold an experiment, 
particularly as a single arch did not appear so important to the 
navigation of the river as to warrant the risk of its failure in a 
part of the city where the permanent existence of a roadway was 
of great importance, and it was therefore given up, and the South- 
wark bridge of three iron arches was erected in its stead. 

1177. This great work was confided to Mr. Rennie, who com- 
menced it in 1813, and finished it in a most satisfactory manner 
from his own designs in March, 1819, at an expense of ^800,000, 
including the purchase of land and occupied premises required 
to be pulled down for the avenues. This stupendous bridge con- 
sists of three cast iron arches which are segments of circles. The 
centre arch spans 240 (eet, and the two side arches 210 feet each. 
The distance between the abutments is 708 feet, and the extent 
of each abutment is 71 feet, formed of solid masonry. The two 
piers in the river are 24 feet in width between high and low 
water lines, 75 feet long from point to point of the cutwater 
angles, and are 60 feet high from the bed of the river to the top 
of the parapet. Their foundations are sunk about 12 feet below 
the bed of the river, and rest on platforms of timber 2j feet 
thick, supported on the tops of 420 piles, most of which are driven 
24 feet into the earth. The soffit of the centre arch averages 
43 feet above medium low water mark, and the road over the 
bridge is nearly level, being paved in the centre 28 feet wide for 
carriages, and with a flag stone footway of 7 ieet wide on each 
side. Many of the single castings in this bridge weigh 10 tons 
each, and the total quantity of iron is 5,308 tons. The castings 



OF IRON BRIDGES. 661 

used in this bridge were executed by Messrs. Walker & Co. of 
Rotterdam, in Yorkshire, above 200 miles from the location of 
the bridge, and the masonry and fixing was contracted for by 
Messrs. Joliffe and Banks, and such was the precision with which 
the work was executed that the centre arch only sunk f of an 
inch on the removal of the centring. The strength of this bridge 
depends upon eight ribs of cast iron plates so proportioned as to 
form an arch of equilibration, and maintained in their parallel 
positions by four oblique iron braces in each arch running from 
the crown on each side to the abutments, and by a number of 
connecting pieces fixed between the ribs. The roadway, which 
is formed on cast iron plates, is supported by straight iron bars 
proceeding from the tops of the ribs, every alternate one of which 
is vertical, while the next radiates from the centre of the arch; 
and where these cross each other an arched tie is introduced to 
connect them together and add to the general stiffness of the fabric. 

1178. Vauxhall bridge, built by Mr. James Walker between 
1813 and 1816, consists of nine cast iron arches, each 78 feet in 
span, and rising 29 feet, forming with the piers, which are of 
Kentish rag stone, a bridge of 860 feet long, which was finished 
for ^£150,000. The arches of this bridge being smaller than the 
last no radiating bars are introduced to carry the iron platform 
of the road, which is supported upon the piers, the crown of the 
ribs, and by the verticle standards placed at equal distances on 
each side of the rib, tied together in the middle of their height 
by a horizontal string-piece, while their tops are united by Gothic 
arches, which gives the whole structure a very light and Elegant 
appearance. Ten parallel ribs are used in each arch of this 
bridge. 

1179. Cast iron bridges have been constructed in many other 
places, but the two above described have been introduced on ac- 
count of their being the largest experiments yet made with this 
material; and as they have both stood the test of 20 years trial 
without any symptoms of failure or decay, either from expansion, 
contraction, oxydation or other cause, there cannot be better 
evidence of cast iron being a good and serviceable material for 
bridge building when properly used and disposed. 

1180. It now only remains to make a few observations on the 
means of using or putting the materials together for the forma- 
tion of arches, and the building of bridges. As arches of stone or 
brick must commence at their springings or abutments, so these 
demand the first consideration, since the stability and duration of 
every arch depends, in great measure, on their perfection. The 
first and greatest attention of the Engineer must consequently be 
given to the solidity of the foundations of his piers and abutments, 



662 OF IRON BRIDGES. 

by driving piles and removing all soft and slippery soil, until a 
firm and solid footing is obtained. This is especially necessary in 
bridge building, because it often happens that the banks of rivers 
are composed of sand or soft mud, brought down and deposited 
by the stream, and such loose soil is of course not trustworthy. It 
is therefore often necessary to carry the land abutments a con- 
siderable distance from the sides of a river, in order that they 
may take hold of, and be resisted by solid ground; and as this will 
occasion a great expense in mj^sonry or brick- work, so land abut- 
ments are very frequently made hollow by introducing arches 
that stand vertically into them to save this quantitity of solid 
work. The approaches to every bridge should be made wider 
than the road upon it, to prevent accidents and allow facility of 
passing, and the parapet walls or other side fences are therefore 
generally made to curve or open as they leave the bridge, and 
those continued walls or side fences, when they arrive on solid 
ground, are called the wings or wing walls of the bridge. This 
circumstance offers an opportunity which should always be em- 
braced, of making the abutments wider than the bridge itself, 
and thus the lateral pressure is extended over a larger portion of 
ground, and is the better able to withstand the pressure that may 
be exerted. Wing walls, therefore, although they may be thin 
above ground, and appear as if they were constructed merely for 
the safety of passengers, are frequently thick and massive under 
the soil, and are carried out in a diverging direction until they 
meet and abut upon solid ground, while they are united by a ver- 
tical arch next the bridge, in order that the lateral pressure of 
the bridge may be transferred to the solid ground; and if the 
bridge is wide, three or even four of such walls are built in the 
direction of the bridge, each pair of walls being terminated by an 
arch that presents its convex surface to the pressure. These 
walls may be horizontal in their courses, or depressed into the 
ground, according to the form of the arch, for a semicircle or 
semiellipse will require level abutments to spring from, while all 
others should incline like skew backs or have their joints and bot- 
tom foundations radiating or vertical to the entrados or inside of 
the arch, in order that they may receive the pressure in a direc- 
tion as nearly vertical as possible to their surfaces. Each arch- 
stone or voussoir, before it is carried to its destination, must be 
regularly cut or dressed to the form of a wedge, the two beds or 
sides of which must also be so cut that when laid in its proper 
place the joints may radiate, so as to be correctly vertical to the 
entrados, while that which is to be the underside of the stone 
must be hollowed out, or have the concavity of the arch given to 
it, otherwise the entrados of the arch, when exposed to view by 



ON BUII.DING BRIDGES. 663 

the removing of the centring, will appear as formed of small flat 
planes, thereby destroying the beauty and regularity of the arch. 
To obtain this precision of form, the large boarded platform be- 
fore mentioned as being necessary for the construction of the cen- 
tring, must be again resorted to. Upon this, the exact curve of the 
entrados must be accurately set out, together with all the vous- 
soirs of their actual size, with the directions the joints are to take; 
and this done, thin mould-boards are fitted exactly to the lines so 
produced, and these are delivered to the masons that the stones 
may be cut to correspond with them. Should any one stone be 
too small to form a complete voussoir, another must be fitted 
to it, so as to complete the full size and carry out the directions 
of the joints; and stones so cut and formed must of course be 
used in positions, in the real arch, corresponding with those on 
the platform. The stone being finished a Lewis hole must 
be made in its upper part, in such a position, as to its centre 
of gravity, that it can be raised and lowered in, as nearly 
as may be, the position it is to occupy in the arch, so that 
when lowered into its proper bed, it may not require twisting, 
turning over, or shifting to such an extent as may disturb the 
cement or mortar previously spread in as thin a layer as possible 
to receive it. If the stones are large and heavy, the mere juxta- 
position of the two faces with the interposed mortar will be suf- 
ficient to retain them in their places in small arches. When the 
arches are large and heavy, dowells or cramps, or even both, are 
made use of to connect the stones together so as to prevent the 
possibility of their sliding over each other. In building Black- 
friars bridge, Mr. Mylne introduced a cubic foot of hard stone by 
letting it half way into each stone between every joint of the arch 
stones; and his piers, built of large blocks of Portland stone, are 
dove-tailed togjether by sound oak. In all cases the lower part 
of the spandrell or space contained between thespringings of any 
two arches in a bridge, or between the arch and its land abut- 
ments, must be filled up with solid masonry, that one arch may 
bear or abut against the next to gain strength in the haunches. 
In Westminster and Blackfriars bridges, the joints of this filling 
in take the same radical direction as the joints of the voussoirs; 
but in the Southwark bridge, this filling in is in horizontal courses, 
but the voussoirs are knee-jointed, which answers the same pur- 
pose as to solidity and firmness; and in both the last bridges this 
filling in is surmounted by an inverted arch covering each pier, 
and working into the main arches, which effectually prevents the 
filling in from rising by the swelling of the haunches should they 
have a tendency to do so. 

1181. In building an arch, since the work must commence from 



664 ON BUILDING BKIDGES. 

the springings or lowest points, the voussoirs must be piled or 
placed on each other with as little mortar as possible, each stone 
being made to slide into its bed if possible until its under side is 
brought into close contact with the lagging of the centring, and 
then it is driven into close contact with its fellow stone by the 
blows of a rammer or beetle used cautiously, because the vibra- 
tion thus produced in a heavy stone, does more to settle it or bring 
it to its bearing than the force of the blows, which might break 
the stone. In commencing an arch as before observed, (1079,) 
little strain falls upon the centring for the first 25° or 30°, espe- 
cially in semi-arches, as will be apparent upon inspecting the 
voussoirs composing the arch in Fig. 254, when if a perpendicular 
line (representing the direction of gravitation), should be let fall 
from the centre of gravity of any of the first four stones from the 
bottom, it would fall within the supported base of that stone; con- 
sequently, these stones would be upheld by those underneath them 
rather than by the centring; but as we proceed higher up, such 
lines would fall upon the centring. Hence it follows that both 
feet of an arch must be began and carried up simultaneously, 
otherwise an inequality of pressure will be induced upon the cen- 
tring, which would cause it to bulge or protrude on the side oppo- 
site the load, thus deranging its figure. An arch must therefore 
always consist of an odd number of voussoirs built or piled upon 
each other until they meet at the top or crown, where the last 
space in the centre is filled up by a single voussoir, usually longer 
and larger than the rest, called the key stone, for it is this stone 
which locks up or finishes the arch, and enables it to stand after 
the centring is withdrawn. The key stone therefore requires to 
be cut very accurately to a template or mould board, fitted to the 
place it is to occupy, and it is sometimes introduced dry or with- 
out mortar, though a little finely sifted thin mortar is beneficial 
by enabling it to slide better into its place, into which it is ram- 
med down, or urged by a heavy temporary pile of stones built 
above it. 

1182. In pursuing the foregoing balancing plan of producing 
an equal load or weight on each side of the centring, perfect secu- 
rity is not always obtained, for unless the framing is perfectly 
strong and immutable in its figure, the loading of the haunches 
■will cause it to rise in the crown, which was the difficulty that 
occurred to Perronet in building the stone bridge at Orleans in 
France, upon the much extolled centring of Hupeau as before 
described (1076.) See Fig. 253, PI. VIII. On beginning to fix 
the stones of this arch in the usual manner, it was found that the 
top of the frame rose very much; it was therefore loaded with 
heavy stones on the crown to prevent this etTect; and now it sunk 



ON BUILDING BRIDGES. 665 

as remarkably. This showed that the lower polygon was giving 
very little aid. M. Perronet then thought the frame too weak, 
and he inserted the long beam 6 e on each sifle, making a diagonal 
to the quadrangles, and very nearly in the direction of the lower 
beam ab, but falling rather below its line. He now found the 
frame abundantly strong, for the truss became completely chang- 
ed, and now consists of only the two long sides with the short 
straining beam lying horizontally between their two heads. The 
whole centring now consists of one great truss a e ib, and its long 
sides ae,ib are trussed up at B 6 and /A. Had this simple idea 
been made the first principle of construction, this centring would 
have been excellent. The angle ab e might have been about 
176°, and the polygon b c g h employed only for giving support to 
this great angle, so as not to allow it to exceed 180°, M. Per- 
ronet also found that the joints of 6 c into the foot of the post e c, 
were about to draw loose, and he was obliged to bolt long pieces of 
timber on each side of the joint embracing both beams. These 
were evidently acting the same part as iron straps would have 
done; a complete proof that, whatever may have been the original 
pressures, there was no abutment now at the point c, and that the 
beams which met there, were on the stretch instead of in a state 
of compression; consequently, their office would have been as 
effectually performed by iron rods as by stiff beams of timber. 
There is no objection to the crown of an arch rising in a very 
slight degree during its construction, because when the centring 
is struck that is the part that always sinks, and it may sink to such 
a degree as to bring the arch to its first intended regular form. 
1183. The arch being finished, must next be examined on its 
upper surface to ascertain whether any of the joints have opened 
from a change of figure during its erection, and if so, where it 
will require loading or weighting to bring it back to its proper 
form; but no hard material should be introduced into such open- 
ings, because they cannot be effectually filled, and if the angular 
faces of the voussoirs have been properly shaped and well worked, 
such materials might prevent the stones from coming to a close 
and even bearing as they will otherwise do. The modern prac- 
tice of loading an arch, is not to fill soil into the spandrells, for 
the reasons before given (1168). But to build brick walls parallel 
to each other, from one arch to another, in the lengthwise direc- 
tion of the bridge, carrying them up to the height of the crown 
of the arch, and covering them over with flag or slab stones to 
receive the marl or other earth that is to form the bed of the 
road, or arching them over when stones cannot be procured. By 
this process, which was adopted in the Waterloo bridge, the arches 
are stiffened and strengthened at the same time that the haunches 
84 



666 ON BUILDING BRIDGES. 

and facing walls are relieved from that pressure, which otherwise 
might prove detrimental to them; and should the weight not be 
sufficient in any part^ it can always be increased by partly filling 
the channels between the walls with rubble stone laid in grout. 
When finished, the upper surface of the arches between these 
walls, must be carefully paved with bricks or flat stones laid in 
cement to prevent any water sinking or percolating into the 
arches and piers; and the parallel walls have drain holes left in 
them, over each pier, that they may communicate with each 
other; because stone bridges are never roofed over, and some rain 
water will always find its way through the roadway, and is col- 
lected in these recesses, from whence it is permitted to run off 
through small iron pipes introduced for the purpose between the 
stones of the arches, or may be carried down by pipes concealed 
in the facing stones of the piers. 

1184. The bridge being so far finished, the centring should be 
released by relaxing its wedges before the facing, spandrel!, and 
outside parapet walls are built upon the arches; because a trifling 
change of form in the arch may occur by its settlement, with- 
out impairing its strength, but which might crack and dis- 
figure the external face walls; but if they are not built until the 
arch has taken its final set, there will be no danger of their being 
afterwards deranged or disfigured. 

1185. The stones of the facing walls of bridges are differently 
disposed, according to the taste of the builder. Thus in West- 
minster bridge, the joints are all made to radiate in the directions 
of the joints of the voussoirs, until they intersect the piers, as 
shewn at Fig. 269. In Blackfriars bridge, the joints are horizon- 
tal and parallel, and the stones that intersect the extrados, are cut 
to its curve; while in the Southwark and new London bridges, the 
joints are horizontal; but instead of the intersecting joints being 
cut to the curve of the arch, the voussoirs of the haunches are 
made to project beyond the regular curve of the extrados, and 
are cut into horizontal and nearly perpendicular forms, so as to 
meet the face wall stones in the manner shewn in Fig. 255, and 
then the work is said to be knee jointed. 

1186. The arches of a bridge are usually surmounted by a bold 
projecting cornice, which is introduced rather to add beauty than 
utihty to the erection. Above this the parapet walls are built 
for the security and protection of the passengers, and in order 
that they may not obstruct the view of the water below, they 
seldom exceed 3 or 4 feet in height, and are finished by stone 
balusters with a capping or cornice above them, or by open pali- 
sades or railing of iron, to strengthen either of which the piers are 
usually carried up to the full height of the top capping or cornice 



ON BUILDING BRIDGES. 6G7 

which runs in common over them. A row of such balusters is 
called a balustrade, and such a one is applied to the sides of stair- 
cases; but the word baluster is frequently corrupted into banister, 
which is improper. 

1187. From the nature of a voussoir, it will be apparent that 
ordinary bricks are unfit for constructing arches under all cir- 
cumstances, because the necessary wedge-like form cannot be 
obtained from a solid having parallel sides. In a brick arch of 
small radius, even admitting that the bricks touch each other in 
the intrados, they must diverge or separate at the extrados, and 
the wide joint thus occasioned can only be filled up with mortar, 
a material not calculated to resist pressure under such circum- 
stances. The large mortar joints at the back must be filled up 
by driving in wedges of slate or stone, but these often produce 
unequal pressure, tending to break the bricks, or to disturb the 
regular settling of the arch, by which its figure may be distorted 
and its strength impaired. If on the contrary, the arch is of very 
large radius, the brick joints will become so nearly parallel, that 
this inconvenience may not be felt; but the bricks must be very 
good, hard, and well burnt to sustain the enormous pressure of a 
large arch and the work above it without crushing, as in the case 
of the Highgate archway. Bricks are sometimes moulded in the 
wedge or voussoir shape, expressly for constructing arches, and 
then they are less objectionable. 

1188. In order to meet these difficulties in constructing brick 
arches, it is customary to lay them in thin concentric rings which 
do not bond into each other. Thus the lowest ring may be of 
half brick or 4j inch work, made smooth on the top, and any 
number of successive rings of the same kind of work may be built 
upon it; in which case the radiating joints will be so short as to be 
nearly parallel. Or if the arch is large the bricks may be used end- 
wise, thus producing nine inch rings to succeed each other. Either 
of these methods will produce a good and strong arch for ordinary 
purposes, especially if exceedingly thin mortar joints are used be- 
tween the bricks. But when the load to be supported is very 
great, there will always be a danger in the rings not settling 
equally on account of the upper rings having more bricks and 
more joints in them than the lower ones, and should this occur the 
pressure may become transferred to a single ring while we sup- 
pose it to be borne equally by them all, and the arch may in con- 
sequence fail. The best and safest way of building a large brick 
arch is therefore to imitate voussoirs as far as possible by building 
blocks of brick-work of bricks placed with their ends towards the 
entrados, and four or five courses thick, and to alternate these 
with bricks, laid in rings, which may extend to two or three times 



668 ON SUSPENSION BRIDGES. 

the width of the voussoir, as shown above the centring in Fig. 
257. This bonds the work better together, and produces a nearer 
approximation to the advantages of a stone arch than any other 
mode of using bricks. 

1189. It was intended to have closed this chapter by some ac- 
count of the suspension bridges which have been erected. But 
the work has extended so much beyond the bounds into which it 
was originallyintended to be confined, that we must be satisfied with 
stating that these are bridges consisting of several iron chains, not 
formed of small Hnks like cables, but of whole bars of iron jointed 
at their ends, passed over a high gate or tower, being the access to 
the bridge on each side of the river, while their extreme ends are 
firmly attached to large and ponderous stones, that are sunk a 
great depth into the ground on each side of the stream. The 
chains hang in parallel festoons over the river between the sup- 
porting towers, and carry a number of vertical bars of iron that 
are attached to, and hang down from them, for the purpose of sup- 
porting beams of wood or iron hanging horizontally in the direction 
of the stream, and serving as joists to support a strong planked 
platform or roadway that extends across the river. Five sets of 
chains are commonly used, and five sets of vertical suspending 
bars hang from them, thus dividing the width of the bridge or 
platform into two carriage-ways in the middle, and two foot-ways 
at the sides, which are separated from each other by fences in 
pannels attached to the lower ends of the vertical suspending bars. 
The most magnificent bridge that has ever been constructed on 
this principle, is at Bangor, in North Wales, over an arm of the 
sea running between the Isle of Anglesea and Cardiganshire, call- 
ed the Straits of Menai. The width of water is so great that it 
was not deemed safe to place the obelisks or towers for supporting 
the chains upon the shores, but they, like other bridge piers, are 
built in the water, at the clear distance of 552 feet asunder. They 
are formed of massive stone and rise 173 feet above low water 
mark. These towers carry metal rollers on their tops over which 
the chains pass and then descend to the rocks on the opposite 
shores, to which they are very firmly attached. The platform or 
roadway is wholly of timber for lightness, notwithstanding which 
the chains, supporting bars, and platform between the two towers 
weigh no less than 650 tons, which immense weight is supported 
at the height of 121 feet above low water mark; so that very 
large ships sail under this bridge without striking their top- 
masts. This stupendous bridge, which is in the direct mail road 
of communication between London and Dublin, was designed and 
executed by Mr. Telford, and is found perfectly stable and secure, 
having withstood the test of much travelling and many heavy 



ON SUSPENSION BRIDGES. 669 

gales of wind. On the 23d December, 1835, a storm occurred 
that it was feared would have carried away the bridge, as it 
was thrown into so violent a state of undulation that parts of 
the platform were elevated and depressed as much as 16 feet. 
This gale lasted twelve hours, and on its termination all the mis- 
chief that was done wks the breaking of some of the flooring 
planks, which were repaired the following day, at the cost of a 
few dollars. 

1190. Several bridges on this construction have since been 
erected, and among others one over the Thames at Hammersmith, 
four miles west of London, by Mr. Tierney Clark, which is justly 
admired for its elegance of design. This mode of constructing 
bridges it is believed originated in China, where ropes, instead of 
chains, were used. The advantages attending them are, that they 
require no centring during their erection, and that they find their 
own state of equilibrium, in consequence of which, if temporary 
derangement of figure occurs it immediately corrects itself, which 
cannot be the case in bridges of the ordinary construction. Be- 
sides which, from the stability of their equilibrium, suspension 
bridges require much less material for their formation than any 
other kind of bridge, which, with the absence of centring, causes 
them to be much cheaper than any other mode of construction. 
In some cases the supporting towers are made of hollow skeleton 
framing of cast iron, supported on plinths or foundations of mason- 
ry or brick-work. 

1191. Arches are often built wholly underground, for the pur- 
pose of supporting the earth after excavations have been made 
through hills for the purpose of carrying roads or canals through 
them, and they are then called tunnels. The Highgate tunnel 
(1173) was of this description. The grand junction canal in 
England, which connects the north and south part of the island 
together, runs through tunnels in several places, some of which 
are two miles long; and the celebrated tunnel under the river 
Thames in London, now in progress by Mr. Brunell, is to open a 
dry road communication under the river instead of over it. In 
tunnels, the arch work lines the whole opening both above and 
below, instead of extending over the top as in bridges. A tunnel, 
therefore, may be said to consist of an arch or vault, built or 
standing upon an inverted arch or vault. The term vault is used 
to express a continued or extended arch. An arch may be com- 
posed of a set of single voussoirs, or even need have no visible ex- 
tent of soffit, as when an arch is introduced as part of a wall; but 
a vault always has extension, so that a room with an arched ceil- 
ing, is always said to be vaulted rather than arched over. In 
this sense the arch of a wide bridge may be <:alled a vault. The 



670 OF TUNNELS. 

height of tunnels is generally greater than their breadth, so that 
their transverse sections present an elliptic rather than a circular 
form, for when tunnels are circular, they are called culverts, 
which are used for conveying small streams of water under navi- 
gable canals and roads. A culvert, therefore, is a complete cir- 
cular arch, or arch continued all round, as in Fig. 49, PI. II., while a 
tunnel is generally an elliptic arch of the same description, notwith- 
standing which a tunnel may be circular. The Thames tunnel is 
not a regular ellipse in its section, but is oval or egg shaped, the 
upper part of the arch being more acute than the lower, which is 
considered the best and strongest form. In canal tunnels, the water 
occupies the lower or inverted arch, a part of which is taken off 
by a battered wall to support the horse towing path which ex- 
tends through the tunnel, and must be wide enough for horses to 
pass in opposite directions. In a road tunnel, the inverted arch, 
or part of it, is filled up with hard materials to form the roadj 
but a culvert or drain must be formed under the road, but within 
the arch, to convey away water if the land is so springy as to en- 
danger the road being kept in a wet state. Should there be no 
means of conveying this water away by natural fall of the coun- 
try, it must be raised artificially by pumping, or even by the con- 
stant working of a small steam-engine, which is the case with 
the Thames tunnel. As all tunnels are dark, except at a small 
distance from their open extremities, they are frequently lighted 
by lamps; and gas lighting is particularly applicable to this pur- 
pose, from the facility with which gas may be conveyed by tubes 
within the arch. When tunnels become so long that it would 
be expensive and inconvenient to remove the earth dug out, or 
the materials for the arch to be carried through the extreme ends, 
they are worked by shafts or vertical cylindrical holes like wells, 
through which the materials are drawn up or let down. These 
shafts are bricked round and left remaining for ventilation, to 
admit light, and to facilitate future repairs. 



671 



CHAPTER XII. 

ON THE PRACTICAL APPLICATION OF THE FOREGOING PRINCIPLES. 

Section I. — Of Rail-roads. 

1192. The subject at which we have now arrived, would be 
endless, were an attempt made at pointing out even the most com- 
mon and ordinary applications which the Engineer will have 
occasion to make of the principles we have endeavoured to lay 
down. We must, therefore, be content with pointing out a few 
of the leading objects to which his attention may be called. Road 
making is one of these, and it is presumed that the information 
conveyed in our 4th, 5th, 6th, and 7th chapters, when combined 
with practice, will prove amply sufficient on this head. As the 
perfection of roads consists in their being level, smooth, hard, and 
dry, all these objects are most effectually obtained by rail-roads^ 
and accordingly their construction demands attention. Of the 
several modes of conveyance, navigation has been preferred as 
being the most economical; but there are many situations in which 
natural water courses do not exist, and in which artificial ones 
cannot be made from want of water, or such inequality in the 
surface of the country as will not permit its use, and then of 
course roads must be resorted to. Independent of this, there are 
reasons why a road, and particularly a rail-road, may be preferred 
to water conveyance even where it can be had. Among these a 
country may be subject to great drought in the summer, or to severe 
frosts in the winter, or to both of them, so that in the summer its 
rivers and canals may be dry, and in the winter may be frozen 
up, and thus rendered useless throughout a large portion of the 
year; but the first of these effects does not apply to rail-roads, and 
the second admits of remedy. 2ndly. Water courses are fre- 
quently more tortuous or crooked than roads, and as the resistance 
to bodies moving through water increases rapidly with their velo- 
city, and is not felt to the same extent when passing through air, 
a much greater velocity of motion can be obtained by the same 
power on a road than on a canal or river. 3dly, Rail-roads oc- 
cupy much less land, and occasion little inconvenience to land 
owners. They are executed much more cheaply than canals, 
cost less to keep them in repair when finished, and frequently 



672 OF RAIL-ROADS. 

possess the advantage of conveying goods and passengers to and 
from their required points without change or the expense of re- 
loading, while in water conveyance, there is generally land car- 
riage and reloading to the place of shipment, and the same again 
at the termination of the navigation to convey goods to their 
ultimate destination, while rail-roads often extend from one point 
to the other, and even into warehouses, and thereby produce saving 
of time, labour, and expense. The only disadvantage of a good 
rail-road is, that a given weipht of goods requires a greater power 
to move it than on water, but as greater celerity is obtained, this 
additional power is kept in action during a shorter time, thereby 
frequently producing ample compensation. 

1193. Railways ditTer from common roads, and derive their 
superiority from two particulars, first, greater pains is always taken 
in their construction to insure either a truly level surface, or one 
of uniform ascent and descent, without the undulations or inequali- 
ties to which the best roads are subject; and secondly, from the 
surface itself being hard, smooth, and free from inequalities. 
Canals appear to have existed from the most remote antiquity, 
yet it is singular that no account of the formation of a railway 
should be met with until about 1620, when it seems they were 
first adopted in the coal mining districts of Newcastle upon Tyne 
in the north of England, for conveying coal from the pits to the 
sea for embarkation. As immense quantities of coal were con- 
veyed in carts heavily laden and constantly travelling over the 
same track or road, they would stand in need of constant and ex- 
pensive repair, to avoid which it appears that timber sleepers 
were laid across the road at 2 or 3 feet from each other, and upon 
these long pieces sawed and well squared, were placed the whole 
length of the road, and on each side of it being fastened down by 
wooden pins or pegs, so that the cart wheels might run upon 
them. On the ordinary road, 17 cwt. was considered a full load 
for a horse and cart, but with this imperfect kind of rail-road, the 
load for one horse was increased to 42 cwt. It does not appear 
that wheels different from those used on common roads were 
adopted; consequently, the wear and tear of the timber tracks 
must have been excessive; and the only improvement that was 
made for many years, was that of facing the rails when finished 
with an extra covering of board for the wheels to run upon, and 
this could be taken up and renewed when worn out, without the 
more expensive operation of disturbing or renewing the substruc- 
ture. 

1194. The next improvement in order of time appears to have 
been the use of cast iron as a substitute for the wooden rails, and 
these were tried on a small scale at the Colebrookdale iron works 



PROGRESSIVE IMPROVEMENT OF RAILWAYS. 673 

in Shropshire about 1767, at the suggestion of Mr. Reynolds, one 
of the partners in that concern. About this same time cast iron 
wheels, turned in a lathe, and made with great truth and accu- 
racy, began to be used, and then it was that the great advantage 
of these roads became apparent, for the advantage to be gained 
by a rail-road depends in a great measure on the perfection of 
the workmanship bestowed upon it, to make it truly smooth and 
level, and on making the carriages that run upon it as free from 
friction and inequalities of motion as possible; and in this a rail- 
road differs materially from a canal; for however roughly that 
may be executed, still, if it is capable of holding water, boats can 
navigate it with no other impediment than what the resistance 
of the water offers to their motion. But in a rail-road all de- 
pends upon exactitude and perfection of workmanship. If a plane 
be perfectly hard, smooth, level and straight, and the wheels of 
the carriage perfectly hard, smooth and cylindrical, the motion of 
such carriage can be impeded only by the resistance occasioned 
by the friction of its axles. It is therefore necessary, in the con- 
struction of railways, to ascertain distinctly those circumstances 
which together make up the great resistance seen in practice. 
By a reduction of these we are not only benefitted by a saving in 
.the cost of draft, but by a proportional diminution in the expense 
of repairs, because if the rails are not well laid and steadily fixed, 
or their joints project, so as to produce obstacles to motion, while 
the wheels intended to run upon them are irregular or out of 
truth, such a railway will not afford the advantages expected from 
it, and will soon destroy itself by its own imperfections. 

1195. On the first introduction of cast iron rails, it was believed 
this metal would not answer from its being brittle, and breaking 
under the enormous loads which it was found possible to draw 
upon it. This led to the next stage in improvement, viz: distri- 
buting the load into a train or number of carriages one behind the 
other, but connected together, and then the cast iron plates were 
found perfectly effective; for notwithstanding a single pair of 
parallel plates w'ould not sustain the load, yet when it was distri- 
buted over a great number of them, they carried it without difE- 
culty, and cast iron became extensively used. 

1196. A rail-road or railway is nothing more than two continu- 
ed lines of iron or other hard material laid or disposed on a road 
in such manner that the two opposite wheels of a carriage shall 
run one upon each of the lines prepared to support them; and to- 
obtain the full advantage from this contrivance, these lines should 
remain right lines and parallel to each other, and incapable of 
sinking or varying from the position originally given to them; and 
the wheels should be perfectlv round and true, move with as little 

85 



674 OF RAIL-ROADS. 

friction as possible, and some expedient must be adopted for pre- 
venting the wheels from slipping off or leaving the lines so pre- 
pared for their support. We shall endeavour to point out the 
means that have been resorted to for obtaining these objects, and 
such others as are necessary to constitute a good and perfect rail- 
way. 

1197. Railways are constructed in five distinct methods: 1st. 
of cast iron plates, which are flat and smooth on their upper sur- 
face for the wheels to run upon, but having a flanch or feather 
rising vertically on one side of the plate, so that its cross section 
presents a right angle or is like the latter j . The wheels to run 
on these plates are simple cylinders, and the use of the vertical 
flanch or feather is to prevent the wheels from getting off the 
rails, for which purpose th,e projecting flanches in laying the 
plates must both be on the outsides, or on the insides of the 
double parallel track. 2ndly. Cast iron plates, with flat and smooth 
tops, but without any vertical flanches. When these are used 
the flanches are formed upon one side of each wheel, and the 
wheels are so disposed in pairs upon the same axletree that the 
flanches upon the two wheels embrace or take in the two paral- 
lel rails, or else the flanches must be placed inwards or next to 
each other, so that they may fit in between the two lines of rails. 
3dly. Wrought iron bars of from two to three inches wide, and about 
three-fourths of an inch thick, having countersunk holes punched 
through them at from six inches to a foot asunder. These bars 
are fixed to rails or beams of timber by nails or spikes, with coun- 
tersunk heads fitting the holes, so that when driven they may 
not project above or interfere with the regular smooth surface 
produced by the iron bars. This railway is the same except as 
to materials and construction as the second method, and of course 
the same flanched wheels run upon it. 4thly. Instead of providing 
a flat surface for the wheels to run upon, as in all the varieties 
above named, wrought or cast iron bars or rails are fixed with 
their thin edge uppermost, and standing some height above the 
level of the road, in which case the wheels may have single 
flanches as before, or a groove or cavity may be formed in the 
edge of the wheel by making it like a pulley, such groove being 
wide enough to receive the upper edge of the rails which are now 
called edge rails, 5thly. The edge rail may be used singly, if ele- 
vated by pillars above the road to such a height as to permit the 
load to hang down on each side of the rail, which constitutes Pal- 
mer's single railway, 

1198. Whichever method of construction may be adopted, the 
preliminary and preparatory steps to be taken by the Engineer 
are nearly alike. A survey of the country and its map must be 



PROGRESSIVE IMPROVEMENT OP RAILWAYS. G75 

prepared. The several lines, (when more than one are contem- 
plated,) must be carefully levelled in order to determine that 
which shall be selected as the most level and the most elevated, 
to insure the work from inundation, and because it is easier to 
convey loads down than up a slope. A profile of the surface of 
the intended line must then be made, and so much earth-work 
wiU be necessary upon this as will reduce the whole length of 
line to a dead or true level, or to a very gentle and uniform slope, 
by cutting through hills and filling up hollows. When large hol- 
lows or vallies occur, or when streams have to be crossed, bridges 
will be necessary for carrying the railway over; and as streams 
are generally found in low or depressed positions, the piers of such 
bridges frequently require to be carried to a great height, be- 
cause a railway will not admit of those elevations and depressions 
which are of no importance in a common road where we should 
depress the road, or go down hill to the bridge, and up hill after 
having passed it. But in a rail-road the bridge must be brought 
up to the level of the road instead of accommodating the road to 
the level of the bridge. On this account a rail-road cannot 
always be carried in the straightest or nearest direction, but has 
to be conducted through the most level track of country, or very 
heavy expenses of earth-work must be incurred to render the line 
level. On this account forming tunnels through hills sometimes 
becomes necessary, both in ,»'ail-road and canal works, as without 
them works that require to be level might be effectually stopped, 
or would have to run in very circuitous routes to preserve their 
level. 

1199. The necessity of keeping common roads dry has been 
before insisted on (418) but this is still more necessary in rail- 
roads, for the purpose of maintaining the level and right lined 
position given to the rails; for if some are supported on drj^ and 
others on wet ground, the latter will inevitably sink, unless pre- 
cautions are used to prevent it. One of the worst enemies a rail-^ 
road has to encounter is frost, for if ground is wet it will swell and 
heave up the rails that are placed upon it when it freezes, and 
these seldom settle down to their original bearings, so that the 
line is thrown out of level and adjustment. In all places there- 
fore where injury from frost may be expected, the foundations or 
bearers of the rails should be piled, or buried so deep in the 
ground that frost will be incapable of affecting them. 

The site of the rail-road being prepared, the method of laying 
down ^nd fixing the rails is nearly the same, whichever kind of 
rail shall be adopted; for in most of them sleepers must be placed 
across the road for supporting them, and these may be of timber 
or stone, or a transverse timber peeper may be let into the ground 



676 OP RAIL-ROADS. 

and a large heavy stone, or mass of rubble-work in niortar, may- 
be sunk below each of its ends to give it a firmer bearing and pre- 
vent its sinking deeper. Both these materials are imperfect, for 
timber speedily decays and wants frequent renewal, especially 
when it is buried near the surface of the ground; and although 
stone is free from this defect, there is a difficulty in fixing the 
rails to it in such manner as will prevent their getting loose in 
consequence of the vibration produced by heavy loads passing ra- 
pidly over them. Holes have been drilled in the stones, and plug- 
ged with wood, to receive the spike-nails by which the rails are 
held down, but the sweUing of the wood, by humidity, usually 
splits the stone. 

1200. The first kind of iron railway that was used consisted of 
the first variety mentioned (1194), and the plates were each six 
feet long with holes cast in their ends, by which they were spiked 
down upon the wooden sleepers, the end of one bar touching or 
abutting upon the next throughout the line. These bars derived 
their stiffness and strength from the vertical flanch which projected 
upwards for guiding the wheels; and as all the first railways were 
worked by horses, the sleepers, between the parallel rails, were 
filled in with gravel, to form a path for the horses to walk upon. 
The inconveniences of this mode of construction were soon felt. 
The rails were too long to be stifif and strong, and the horses' feet 
disturbed much dust and small stones, which was thrown upon the 
iron surface, and was confined or prevented escaping on one side 
by the vertical flanch, so that this form of construction was soon 
abandoned. 

1201. The second variety, or flat topped rail without a flanch 
succeeded. This was made four feet long, four inches wide at the 
top; and an inch thick; but such a rail would not sustain the re- 
quired load without some assistance to strengthen it, and accord- 
ingly a semielliptic or parabolic feather or flanch at right angles 
to the, vertical plane of the rail was cast on its underside, so that 
Fig. 157, PI. v., shows the form of such a rail, and a and 6 are 
transverse sections of the two sleepers upon which it is nailed. 
To retain the carriage upon this railway, flanches now became 
necessary on one side of each wheel, and these were so placed as 
to hang down or project below the insides of the rails; and to 
diminish friction and the lodgment of grit and dirt upon the 
rails, their tops were rounded instead of being quite flat. This 
was the only kind of rail-road that existed for a number of years 
in England, and was found very useful and effective in the coal 
and quarry districts, where speed was not so great an object as 
facility of conveyance. The plates obtained the technical name 
of tram plates, and roads formed of them were called tram-roads; 
but the particular form of rail shown in the figure just referred to 



PROGRESSIVE IMPROVEMENT OP RAILWAYS. 677 

obtained the appellation oi fish-bellied rails, from the shape of the 
feather under it, which heing buried in the ground could be made 
of any depth neces.^ary for the strength of the rail. 

1202. The only objections to this kind of railway arose from 
the frequency of the joints, and the difficulty of fixing them per- 
manently to the sleepers, because of the vibration produced by the 
carriages, and the whole being alternately wet and dry causes the 
nails to draw and become loose; and the liability of the cast iron 
bars to break when they are so loosened. This occasioned the 
adoption of the third variety of rail, consisting of common bars of 
wrought iron used of their full length, which is never less than 
twelve feet, and nailed down at short intervals, with nails that 
are countersunk into the bars, upon a railway previously construct- 
ed of hard and durable timber in long lengths, supported, as in the 
other railways, upon transverse sleepers well bedded and support- 
ed by the soil, or when that is soft, by longitudinal sleepers under 
their ends. As far as travelling is concerned this forms a most 
excellent railway, for none of the materials are so brittle as to be 
liable to break, and from the length of the parts the number of 
joints is greatly diminished, and the frequency of nailing prevents 
vibration and the parts becoming loose. From the elastic nature 
of the wood, loaded cars move very smoothly and pleasantly upon 
this road, and it possesses a great advantage, as to passengers, in 
the motion being nearly free from noise. It is therefore a good 
railway as regards the public, but a bad one for the proprietors^ 
on account of the transient nature of the substructure, which, 
being wholly of wood, is subject to rapid wear and decay, and 
consequently to the heavy expenses of renewal. 

1203. When a railway is laid down in a common road, it is ne- 
cessary to keep all its parts at very nearly the same elevation as 
the surface of the road, in order that they may be crossed and 
passed over by common vehicles without obstruction. And this 
is also necessary for the preservation of the railway itself; for if it 
stood above the road, rails would frequently be broken or knocked 
out of their places, by common carts and wagons running against 
and crossing over them. This is, however, very detrimental to the 
action of the railway, because small stones and dirt will be con- 
stantly deposited on what ought to be a perfectly smooth surface, 
and in this way the effect of the rail-road may be diminished down 
to a state differing little from a common road. All the varieties of 
rail, so far described, are more or less subject to this defect, which 
becomes serious when horses are used, because their feet are con- 
stantly distributing mud or dust upon the rails, and rail-roads are 
known to work better in rainy weather, because the rails are 
then clean. Mr. Palmer tried an experiment on a branch of the 



678 OF RAIL-ROADS. 

Cheltenham Rail-road while it was new and in perfect condition, 
to ascertain the resistance of mere dust upon the rails. The rails 
being swept clean, a carriage, with its load weighing 5,264 lbs., 
was put in motion by the application of a force of 36 lbs.; but on 
covering the same rails slightly with dust 43 lbs. of moving force 
became necessary; thus increasing the resistance to motion by 
7 Ibs.f or upwards of one-fifth of the force necessary when the 
rails were clean. 

1204. With a view to remove the resistance from dirt or grit 
Jying on the rails, Mr. Jessop, an eminent Engineer, who was 
employed to form the public rail-road at Loughborough in Leices- 
tershire, adopted the fifth kind of rail, which, by way of distinc- 
tion, he called the edge rail. In this, instead of placing the plates 
flatwise upon the ground, they were placed with their edges up- 
wards, and a rounded or elliptical form of greater thickness than 
the general bar was given to that edge, which was elevated 
above the surface of the road, and wheels with flanches were 
used to prevent the carriages running off the tracks. The edge 
rails first used were bars of cast iron from three to four feet long. 
The upper surface was thick and rounded like the handrail of a 
staircase, and was from two to two and a half inches thick, but 
this gradually tapered on each side, so as to reduce the under 
part of the rail to the form of a plate about three-fourths of an 
inch thick, and of a depth proportionate to the load it had to carry. 
Mr. Jessop, instead of nailing the ends of his rails to the wooden 
blocks or sleepers, as had been before done, lodged and united the 
two contiguous ends of each rail in a small block of cast iron 
made to fit and receive them, and which was called a chair, and 
these chairs were fixed to the tops of large blocks of stone pro- 
perly bedded in the ground, thus producing a much more durable 
and stable construction, and a near approximation to the most 
approved form of railway now generally used. 

1205. In October, 1820, Mr. John Birkinshaw, of the Bed- 
lington Iron Works, Durham, gave the last stage of improve- 
ment to railways by obtaining a patent for wrought iron rails, 
and for improving their form and mode of application. Before 
this time common bars of wide and thin iron had been used in a 
few instances with their edges placed upwards, but they did not 
answer. Mr. Birkinshaw's improvement consisted in passing bars 
of iron of proper size and form, when red hot, through rollers like 
those shown in Fig 127, PI. IV., but within dentations or grooves 
made in them corresponding to the shape of the intended rails. 
In this way, wrought bars with swelled and rounded tops similar 
in section to the cast bars before used, and with a flanch at the 
bottom to promote stiffness, can be produced in lengths of 12, 15 



WROUGHT IRON EDGE RAILS. 679 

or 18 (eet These long bars are fixed in chairs at their extreme 
ends when two bars unite, and likewise at about every 3 feet of 
their intermediate length, and if these chairs are supported by 
blocks of stone of sufficient magnitude, well bedded and fixed in 
the ground, this construction offers as permanent and good a rail- 
road as can be desired. 

1206. The fifth modification of railway before mentioned con- 
sists in using only a single, instead of a double and parallel row 
of rails. This is an ingenious contrivance of Mr. Henry R. Pal- 
mer, a Civil Engineer of London, which he made public in 1824, 
and is stated to be cheaper than the double track, inasmuch as 
only one row of rails is necessary. The writer has doubts as to 
the economy in expense of this plan, because it appears to him 
that the iron columns and extra expense of fixing the single row 
of rails upon them, as he proposes, must be fully equivalent in 
expense, if not more so, than when two parallel rows of railing of 
the common kind are used. 

Mr. Palmer proposes placing columns or supporters formed of 
flat cast iron, feathered or ribbed on both sides (024,) at about 
10 feet apart, or in the event of cast iron being scarce or too ex- 
pensive, driving wooden piles into the ground, or building stone 
pillars throughout the line of railway. The tops of these pillars 
must correspond with the level or plane of the proposed railway, 
which in no case must be less than 30 inches above the ground^ 
but may be more as its surface undulates. Each column or prop 
carries a rectangular cleft on its top for receiving and holding the 
rails, which are proposed to be made of 3 inch deals, (549,) that 
is, pine planks 3 inches thick, and from 10 to 12 inches wide, 
which are to be laid edgewise in the clefts, their upper surfaces 
being covered by wrought or cast iron plates, which are saddle- 
backed or rounded on their upper sides for the wheels to run upon. 
These rails halve vertically into each other within the cleft, and 
a pair of cross wedges are placed in each of them under the 
planks, by means of which they can be accurately adjusted as to 
height and level, but no joint in the iron covering plates must 
occur over a joint or meeting of any two planks. Should any 
derangement in the level or line of surface of the planks occur 
after they have been in use a short time, it can be rectified by 
the cross wedges; but when the whole line has come to its proper 
set or bearing, the whole is to be firmly and permanently fixed 
by screw bolts passed through the cheeks or sides of the clefts, 
and the planks, to hold the whole together. 

1207. The carriage proposed to be used upon this railway has 
but two iron wheels, with grooves in their edges fitting on to the 
iron protecting plates, and disposed one before the other, and 



680 OP RAIL-ROADS. 

fixed by proper diagonal bracing beanns at 5 or 6 feet apart. 
The iron axletrees of the two wheels project on both sides about 
3 or 4 feet, and two rods of iron are fixed on each side to each of 
them in such manner that their lower ends, formed into hooks, 
are a little below the upper surface of the rails, while they pro- 
ject downw^ards at right angles to the axletrees, to which they 
are fixed in an inflexible manner, one at each extreme end, and 
one as near to each wheel as the thickness of the posts and rail- 
way will admit. The body of a common wagon, or boxes made 
for the purpose, are hung on to the four descending hooks, and in 
these the load to be carried is disposed, as nearly divided as possi- 
ble on the two sides in order that the two wagons may balance 
each other. In this disposition the centre of gravity of the load 
is so far beneath the surface of the rail or plane of suspension 
that there will be no tendency to overturn, and as the suspending 
bars are immovably fixed at right angles to the axletrees, no 
great nicety of balancing will be required, since it will require a 
considerable diflference in weight to throw the supports much out 
of perpendicular, and a small deviation will be of no importance, 
because the top of the rail is rounded, and fits the similar formed 
groove in the edge of the wheel. Any number of these carriages 
can be yoked together to form a train, as in other railways, and 
the bottoms of the wagons need only be raised so far above the 
ground as wall ensure their not striking against stones or other 
obstacles. The horse or other motive power is to be applied by 
a towing rope to the front carriage, such rope being so long as 
will not materially alter the line of traction or draught, with the 
varying elevations of the country, since in high or level ground 
the load will be below the horse, but in passing vallies may be 
several feet above him. The towing path is of course made paral- 
lel to the rail and close to the line of posts. The advantages pro- 
posed by Mr. Palmer are, that being a single line, it will cost less 
for its first erection and future repair than the usual double line. 
That it will be less liable to get out of order, and if it does get 
out of line, is easily readjusted by the cross wedges. Having only 
two wheels instead of four, there will be less friction, and the ele- 
vation of the rails w'ill place them above the reach of coarse grit 
or snow. It requires less land for its construction, and may even 
be formed upon the side fence or wall of any bridge for crossing 
a river; and that it affords great facility for loading and unload- 
ing, inasmuch as common wagon bodies with crossbars to receive 
the hooks, may be used for conveying loads, and they may be 
taken from, or lowered down to a common carriage with ordinary 
wheels without discharging the load whenever common road 
transportation becomes necessary. The same crossing places may 



FORMATION OF RAIL-ROADS. 681 

be adopted in this as in any other rail-road, and when it has to 
cross common roads, such roads may frequenlly occur so deep in 
the ground that this railway may pass over them like a bridge, 
or when this is impossible a single rail is made to turn up on a 
pivot at one end, or may be lifted out of its place. In fact, Mr. 
Palmer has provided for every contingency that can happen on a 
rail-road, and there is no doubt but that his plan is not only prac- 
ticable, but may be useful in some cases. 

1208. Now that rail-roads have become ai.i object of national 
importance, not only for carrying great loads, but for a velocity 
of conveyance much beyond what was formerly contemplated, 
they are generally constructed upon roads formed exclusively for 
themselves, and on which no vehicles but those formed for the 
rail-road are permitted to travel, and this ought always to be the 
case when speed is desirable, and particularly when locomotive 
engines are used. Common carts and wagons passing in all direc- 
tions over a railway, frequently injure it, besides which they may 
stand in the way and produce accidents; and when the road is 
exclusively railway, there is no necessity of keeping the rails 
down to the surface of the road, except in crossing common roads, 
since such depression is merely for the convenience of the passage 
of common vehicles; and when the rails are elevated, they will 
be more free from dust and impediment. Railways ought even 
to be fenced in, so as to prevent cattle getting upon them, as they 
frequently occasion delay and accidents. 

1209. The form of wrought iron rail now most used and ap- 
proved, is the edge rail, shewn in cross section at Fig. 270. The 
top part a and h for the wheels to run upon being gently rounded 
and about 2J inches wide. The figure at a has a double flanch 
or base running its whole length on each side, and 6 has this flanch 
on one side only, and c de show the form of cast iron chair for re- 
ceiving and holding the rails. It has a flat bottom plate to bed 
upon the bearing stone, from the middle part of which rises the 
projecting piece e c d. The opening c d should be wide enough 
to permit the bottom flanch of the rail to pass through it, so that 
a chair can be introduced under a rail without taking it up; and 
that done, the rail is fixed in its place by driving the very slightly 
tapered key or wedge y. The best way of fixing the chair to the 
block of stone, is to let the heads of iron screw bolts into holes in 
the stone, which widen as they go down, and to run them in with 
melted lead or iron cement, formed of iron borings, sal ammoniac 
and sulphur moistened with water and well caulked into its place. 
Nothing but the screwed part of the bolt projects, and that passes 
through holes in the bottom plate of the chair, which holes should 
be oval, to permit of lateral adjustment of the chairs to the right 

86 



682 OP RAIL-ROADS. 

lined direction of the rails. It is further advisable to introduce 
a plate of thick sheet lead between the bottom of every chair and 
its stone support, as this not only produces a firmer seat, but pre- 
vents the nuts and keys becoming loose from the vibrations pro* 
duced by rapid loads. One of these chairs and stone supporting 
blocks should be used at about every three feet distance, and the 
joining of two contiguous bars must always take place in a chair. 
Formerly, the plates were vertically halved and pinned together 
horizontally at each joint, so as to unite the whole line together, 
' but this practice is bad, for the contraction and expansion of so 
long a line by changes of temperature, will throw parts of the 
line out of adjustment; but by the above method of wedging, each 
bar is independent, and the trifling change of length that occurs 
in each length is never perceived. The joining of the bars in the 
two parallel tracks of a rail-road ought to be broken, or not to 
occur upon an opposite pair of chairs. 

1210. So far, we have only spoken of single rail-roads, but as 
it is impossible for carriages to move out of their tracks to pass 
each other, so one of two methods must be used to prevent the 
meeting of carriages on the same road. The first is that a set of 
flags or signal poles must be erected along the whole line, at such 
distances as to be visible from each other, and flags must be raised 
to signal that the road is occupied by a car or train, and thus re- 
strain others from going upon it, except in the same direction; 
and the other is to provide short side rail-roads called turn-outs or 
sidings, so that one or other train may move out of the main 
track for a short time while the other is passing. In rail-roads 
of great traffic, neither of these are necessary, because two sepa- 
rate tracks are always provided, one being kept for passage in the 
one direction, and the other for the opposite direction. This of 
course is attended with double expense of every thing that regards 
laying down the tracks; consequently, in railways of less impor- 
tance, the single road with turn-outs is generally adopted. 

1211. The number of turn-outs or sidings, must depend on the 
nature and extent of the traffic; consequently, no rule can belaid 
down for the frequency of their occurrence; but they ought always 
to be placed in positions that command a long extent of view, 
so that trains may see each other and prepare for turning out 
long before they meet. The turn-out is nothing more than a 
short length of rail-road constructed on one side of the main line 
parallel to and as near to it as will permit the two trains to 
pass each other without contact. This short railway is connected 
with the principal fine by curving or sweeping its two ends in 
such manner that they may come into and join with the main 
road. At each termination a long tapered cast iron wedge called 



♦ 



PROVISIONS FOR TURNING OUT, 683 

a switch^ is fixed on a pivot so that its point can turn from one 
track to the other, as shewn in Fig. 271, were a b represents part 
of the main right lined track, d the termination of a turn-out con- 
nected with it, and C the switch, which in its present position 
shuts up the turn-out road, and compels the wheels to continue 
in the track a b. But on moving the switch into the position g, 
shewn in another part of the same figure, the track b e will be 
shut up and the wheels will be constrained to move along bf, or 
into the turn-out, and will be brought back again into their former 
track by a similar contrivance at its opposite termination. These 
switches are usually moved by a series of partly underground 
levers, and a balance weight to fix them in the direction in which 
they may be placed. When trains meet away from a turn-out, 
there is no alternative but for that nearest to a turning out place 
to change its direction of motion, and go back again until it arrives 
at one. Such reversion of motion is produced by reversing the 
direction of power; consequently, rail-road cars and locomotive 
engines must be so constructed that they will move equally 'well 
in either direction. But when horses are used, the team must be 
detached and be yoked to the opposite end of the train. When 
a sudden turn at right angles becomes necessary, it is brought 
about by a turning platform^ which is horizontal and sunk to the 
level of the rest of the railway, and circular that it may turn 
round in a circular brick cavity without impediment. The re- 
volving circle must be of suflicient diameter to receive the four 
wheels of a loaded car when run upon it, and it is maintained in 
a perfectly horizontal position while it moves by a strong vertical 
iron spindle, and a number of sloping or diagonal braces that 
spring from its lower end. The platform turns upon the point of 
the spindle with so little friction, that it can be moved round with 
facility, and thus the car can be put into any direction for pursu- 
ing a new line of rail-road; but of course, the car must be sta- 
tionary upon the platform during the operation. 

1212. No rail-road of great length can be constructed without 
deviations from the right lined direction; and the curve, when 
necessary, should be as gentle or drawn from as large a radius as 
possible; first, because all motion tends to a right lined direction, 
and a loss of power always attends a deviation from that right 
line, particularly in long trains of cars; and secondly, there is 
danger of overturning, or at any rate running ofi" the track from 
centrifugal force when a heavy body in rapid motion changes 
from a right lined to a curved direction, or rice versa. The curves 
lused are always circular, unless irregularities on the face of the 
country forbid such form, and the radii of the segments ought 
never to be less than 300 feet in length, and will be much better 



684 OB' RAIL-ROADS. 

if they extend to lengths of from 1 to 2000 feet. Of course with 
such extended radii the ordinary nnethod of describing circles or 
their segments by a line or wire fixed at the centre, and serving 
as a radius to be carried round, becomes impossible; consequently, 
such curves must be set out upon the ground by means of the 
theodolite, which for this purpose is placed in the centre of cur- 
vature; or if that should be impossible on account of woods, water, 
or other natural impediments to sight, may be placed in some 
point of the circumference, as nearly opposite as may be to the 
concave side of the curve desired. The telescope of the theodo- 
lite may then be moved round through equal spaces on its hori- 
zontal plate, such as 2, 4, 6, or even 10 degrees, and a radius 
having been measured by the chain from the position of the in- 
strument to the point where the curve is to proceed from. The 
telescope must be moved a certain number of degrees, and a set 
of picket staves being set up in the direction in which it now 
points, a second radius exactly equal to the first must be measur- 
ed in that direction. The extreme end of this new radius must 
then be joined to the first, by measuring a right line with the 
chain between the outer ends of the two radii, which line will 
evidently be the chord of the angle subtended at the theodolite, 
and we shall have produced an isosceles triangle upon the ground, 
the use of which is to determine the length of the cord, which 
should not exceed two or three chains. That done, there will be 
no occasion to measure other radii, but the telescope being moved 
through equal an^;ular spaces, and the ends of the radii so produced 
being marked by pegs or picket staves, the one fixed chord that 
has been obtained must be swept from the point fixed in the last 
radius, until it coincides with the new one, and all the points at 
which such coincidence takes place, will of course be in the cir- 
cumference of a circle having the radius first set out. This de- 
pends upon the principle in geometry, that equal angles always 
subtend equal choids of any one circle that is drawn from their 
common summits as a centre. And it equally holds good if the 
summits are on the opposite side of the circle, but then the chords 
will only subtend half the angles that would have been produced 
if measured from the centre. 

121.3. When once a mass of matter in rapid motion has had its 
motion changed from a right lined to a curved direction, it will 
more readily admit of the curvature being increased. Conse- 
quently, notwithstanding it is prudent to make the first change 
by a curve of very long radius, yet, after it has moved on that 
curve long enough to have acquired the motion proper to it, the 
curve may become gradually more bent, or be drawn with a 
shorter and shorter radius to produce greater deflection from the 



OF CURVES IN RAIL-ROADS. 685 

right lined direction. The opposite construction must be observed 
when changing from a curved to a right lined direction; conse- 
quently, if the curve has been gradually contracted, it must 
gradually open again or increase in radius when the curved direc- 
tion is again to be converted into a right lined one; and every 
right lined direction must be so placed in respect to the curves, 
that they may always be tangents to such curves. When a very 
sharp turn is necessary, as for instance when a railway proceeds 
through the streets of a town, or into a warehouse, great length 
of radius is impossible; and the only way of compensating for this 
is by placing the exterior track, or that which has the largest 
radius, a few inches higher than the inner track. This will throw 
the carriage out of level, and cause the motion to be, as it were, 
round the base of a cone. The utility of this principle is fully 
exemplified in circus riding, where the horse and his rider moving 
rapidly round a circle of small radius, are constrained to lean 
considerably towards the centre to prevent their being thrown 
outwards by the effect of centrifugal force. 

1214. The great alteration and improvement which has occur- 
red of late years in the construction of rail-roads, is that formerly 
it was considered quite necessaFy to make the whole line, or as 
much of it as possible, a perfectly true or dead level. This level 
line was carried to as great an extent as nature, when assisted by 
art, would permit; and consequently required deep cutting in high 
ground, and much embankment, or raising up in low places to ob- 
tain the level. At the extremity of the longest continued level 
that could be obtained, when changes of elevation became neces- 
sary they were effected by continuing the railway either up or 
down a regular right lined slope, called an inclined plane, thus 
overcoming the difference of level all at once in a short distance, 
after which, the road resumed its wonted level character. At 
these inclined planes power became necessary both to draw the 
loads up, and to retard the natural velocity of descent in going^ 
down, and the cars or wagons were fastened to a rope or chain by 
which the power was exerted. In some instances, a double 
parallel railway was formed, and the rope by passing over a large 
drum or pulley, at their upper ends, connected them both, so that 
the weight of two or three empty cars descending, would draw 
one loaded car up, and the velocity of motion was regulated by a 
brake or apparatus to produce friction on the drum. This mode 
of proceeding answers very well, whenever there is a nearly equal 
weight of goods to pass in both directions, or where all the heavy 
goods have to descend, which is generally the case in mining ope- 
rations. But if more weight has to ascend, than goes down, the 
counterpoising cars will soon all be at the bottom of the hill. To 



686 OP RAIL-ROADS. 

remedy this, horse power was applied to give motion to the drum 
and raise the carriages, the empty descending ones being used 
merely in assistance of the power. Horse power soon gave way 
to that of the steam-engine, and in all large concerns a stationary 
steam-engine was built at the top of each inclined plane, connect- 
ed with a very strong endless rope, or one united at its two ends, 
which passed over a roller both above and below, so that as one 
half of the rope ascended by the power of the engine, the other 
descended, thus allowing loads to be moved in either direction by 
attaching them to the appropriate part of the rope. 

1215. From the nature of such an arrangement, the inclined 
plane is necessarily right lined, and the rope is borne upon rollers 
to prevent its rubbing on the ground and wearing away, as it is 
not only an important element in the performance, but likewise 
in the expense of the machine, for such ropes are usually from 
five to seven inches in circumference, and are not unfrequently 
from one to two miles in continuous length. Such a length of 
rope is always difficult to manage on account of its expansion and 
contraction with different states of weather, which must be pro- 
vided for in the construction of the machinery; and very serious 
accidents have frequently happened upon these inclined planes; 
sometimes from the breaking of the rope, but more frequently 
from the load being carelessly and insufficiently attached to it. 

1216. Since the introduction of locomotive engines for drawing 
trains upon rail-roads, these costly and dangerous inclined planes 
have ceased to be formed, and stationary engines to be erected; 
because the increased velocity and momentum that is given to 
loads by the employment of locomotive engines, is found fully com- 
petent to carry them up inclined planes, provided the slope is not 
too steep; so that instead of going to a very heavy expense of cut- 
ting, or earth-work, to produce a great length of perfectly dead 
level, the natural surface of the country can be used to a greater 
extent than was at first thought practicable; and instead of accu- 
mulating all the rise or fall into a small space, and overcoming it 
all at once by an inclined plane, it is now distributed as evenly as 
possible over a great extent of line, thus diminishing the rise and 
fall to such an extent that it is barely felt in ascending, and 
should it become too steep for descent with safety, brakes are 
applied to the carriage wheels to increase their friction in mov- 
ing, or even stop their rotation entirely, if necessary. Such a 
distribution of the varying level is called graduating the line, and 
the variations in level are called ^mc^es, which are said to be easy 
or steep, as the slopes are more or less gradual or rapid. As an 
instance of this mode of construction we may take the rail-road 
between Petersburg in Virginia, and the Roanoke river in North 



OF GRADUATING LINES. 687 

Carolina, called the Greensville and Roanoke Railway. Going 
southwards from Petersburg it proceeds 3,219 feet, with a rise at 
the rate of 19 feet in each mile; it then begins to descend 13.70 
feet per mile for the next 4,100 feet, after which it is dead level 
for the next 1,000 feet. It then ascends 32.20 feet in a mile for 
8,750 (eetf and then descends at the slow rate of 5.80 feet in 
a mile for 2,000 feet. It then ascends again at the same rate as 
before, viz: 32.20 feet in a mile for 8,800 feetf then descends 
15.84 feet per mile for 3,000 feet;* thus rising and falling very 
gently through its whole extent, except near its termination, and 
there we find a descent of 50.16 feet per mile for 1,500 feet, fol- 
lowed by a steeper descent of 93.45 feet per mile for 9,100 (eet, 
which again breaks into a dead level, 3,200 feet long, before it 
joins the river. The steepness of these last grades is certainly 
objectionable, but no better line could be found, and as they occur 
near the termination of the line at the Roanoke river, it is stated 
that the difficulty can be overcome by the going and returning 
Engineers helping each other, or by bringing lighter loads up the 
hill, and depositing them in a depot or warehouse there, to be 
carried in larger quantities through the rest of the road. 

1217. When locomotive engines were first tried in the collieries 
of the North of England, by Mr. Blenkinsop, one wheel at least of 
the engine had strong cogs, or teeth, round its periphery, and the 
railway, upon which it ran, was also a toothed rack, with its teeth 
placed upwards, in order that they might engage in those of the 
wheel. This precaution was deemed necessary for fear the wheel, 
to which the engine power was applied, might slip round upon the 
railway without giving motion, or motion with available force to 
the engine to drag loaded cars after it, and it is astonishing that this 
false notion should not have been removed by experiment for 
many years. Now it is well known that such teeth are unneces- 
sary; that the periphery of the iron wheel may be turned in a 
lathe, and made quite smooth, and yet that it will hold upon an 
iron railway with sufficient friction to carry all needful loads, not 
only on level tracts but even up considerable inclinations. 

1218. In the year 1829 the Directors of the Manchester and 
Liverpool Rail-road, in England, were desirous of setting the point 
at rest, as to whether stationary engines with ropes to draw the 
trains, or locomotive engines were the best to be made use of; 
and they therefore referred the full investigation of this subject 
to Mr. James Walker, one of the principal Civil Engineers of 
England, and to Mr. Rastrick, a manufacturer of steam-engines, 

* Account of the Greensville and Roanoke Railway, in the Farmer's Register, 
Vol. v., p. 9. Petersburg, Va. 1837. 



688 OF RAIL-ROADS. 

^A^ho immediately set about a minute examination, not only of the 
circumstances appertaining to the rail-road in question, but of 
several other railways in which both kinds of engines were used. 
The Manchester and Liverpool railway was generally so level, 
that none of its reaches contained slopes rising more than 1 foot 
in 880 feetf except in three places, where they constructed in- 
clined planes. Two of these were each Ij miles long, the one 
ascending and the other descending 1 foot in 96 feet, and the third 
being a tunnel to pass through a hill for entering Liverpool fell 1 
in 48 through a distance of 1^ miles. From the pains Mr. Walker 
took in this investigation, and the quantity of valuable practical 
matter embodied in his report made in March, 1829, it is justly 
considered as a valuable document, containing all the best and 
most important information that could be obtained up to that 
date on the economy and management of loads upon rail-roads. 
The conclusions he arrives at are divided into distinct heads: 1st. 
The power of locomotive engines, or the quantity of work they 
are capable of performing. 2nd. Their consumption of fuel to 
perform that work. 3d. Their annual cost. 4th. The friction of 
ropes in stationary engines. 5th. The cost of such ropes. 6th. 
The wear and tear of wagons. 7th. The accommodation to the 
public. 8th. The comparative safety of the two modes. Each 
of these heads is separately discussed in an able manner, which 
our limits prevent us entering into, but the general conclusion is, 
that "taking the two lines of road as now forming and having 
reference to economy, despatch, safety and convenience, that the 
stationary reciprocating system is the best for putting the rail- 
way into complete working action at once; but should circum- 
stances induce the company to proceed by degrees to proportion 
the power of conveyance to the demand, then locomotive engines 
are recommended generally on the line; but with fixed engines 
and ropes at the inclined planes, to draw up the locomotive engines 
as well as the carriages and goods." 

1219. It thus appears clearly that at this period, locomotive 
engines were considered as incapable of surmounting inclined 
planes of considerable slope. One of the objections made to loco- 
motive engines is that they seldom exceed 10 horses' power each, 
and an engine of this power generally weighs full 10 tons. The 
weight of the engine becomes a part of the load to be conveyed, 
and the power thus lost amounts to about one-tenth of the full 
power when moving the engine only 2^ miles per hour. In the 
stationary engine all its power is disposable for drawing loads 
without any deduction for its own weight, and it may be kept 
constantly at work drawing a succession of loads, while on the 
locomotive plan, each train must have its own engine and sepa- 



OF LOCOMOTIVE ENGINES. 689 

rate fire, and by multiplying these, the expense of fuel will be 
greatly augmented. This is no doubt true, but against it, in the 
locomotive plan no ropes are necessary, and the friction and wear 
and tear of rope amply compensate for the increased expense of 
fuel, besides avoiding the danger of accident and delay from ropes 
breaking or becoming deranged. 

12:<J0. In consequence of this report the stationary engines were 
erected by the Manchester and Liverpool Company; but they 
publicly advertised a reward for the improvement of locomotive 
engines, the conditions of which were, that one engine should 
draw 20 tons on a level railway at the rate of 10 miles per hour, 
with a pressure of steam not exceeding 50/65. on the square inch. 
This announcement caused several new engines to appear on the 
road in Oct. 1829, when they competed for the prize, which was 
awarded to the Rocket, which carried d^ tons exclusive of its 
own weight, and that of its tender, 14 miles within the hour. 
From this time locomotive engines have been gradually improv- 
ing, and in 1830, no less than ten were employed on this rail- 
road, but within three years afterwards they were all thrown 
aside for new engines of nearly double power. The recent im- 
provements in locomotive engines have therefore almost consti- 
tuted them a new class of machines, while no improvements what- 
ever have been made in fixed engines, in consequence of which, 
their use has been quite suspended. 

1221. In June, 1831, an inclined plane was located at Parr's 
ridge, on the Baltimore and Ohio rail-road, and as this rose 197 
feet in a mile, it was intended to place a stationary engine upon 
it; it having been considered as previously established, that no 
slope exceeding 35 feet in a mile could be surmounted by a 
locomotive engine. Some delay occurred in procuring the 
fixed engine, and horses were used for drawing up the neces- 
sary loads. In the mean time the improvement of locomotive 
engines had advanced to such an extent that it was determined 
to make trial of one upon this slope, and on the 22nd of March, 
1836, the engine Andrew Jackson, weighing 8 tons'lO cwt., and its 
tender 4 tons 7 cwt., conveyed one double and three single cars, 
weighing 12 tons 18 cwt., making, with the engine and tender, 25 
tons 15 cwt., up this inclined plane, which is 2,050 feet long, at the 
rate of 5 miles an hour, although the last 100 feet of the line 
rises 201 feet in a mile. The engine and train then advanced 
over the intermediate level, and commenced the ascent of the 
second inclined plane 3000 feet in length, 2800 feet of which 
rises 170 feet in a mile, and then 227 feet per mile. This in- 
clined plane was passed over at between 5 and 6 miles per hour, 
until the engine arrived at the foot of the last slope, where it came 
87 



690 INTERNAL NAVIGATION. 

to a stand; but by disengaging three single cars, weighing together 
5 tons 1 cwL, thus reducing the load to 20 tons 14 cwt. the engine 
advanced to the top of this slope in a steady manner. The steam 
during this experiment was equal to 63 lbs. on the square inch. 
Since this time the greater slope has been cut down and much 
reduced. 

1222. It is obvious, therefore, that the efficient action of loco- 
motive engines can now be extended to inclinations of a much 
steeper grade than was formerly contemplated, even a few years 
ago. But at the same time steep inclinations are very disadvan- 
tageous on rail-roads by losing power. Mr. Knight, to whom we 
are indebted for the foregoing particulars,* ascertained that if 
the friction is 12 lbs. per ton, which he estimates it to be, that the 
useful efTect of an engine when moving on a level plane will be 
reduced to one-half in moving up an ascent of 25 feet per mile; 
to one-fourth on an ascent of 66 feet per mile; and to one-fifth at 
92 feet per mile. Consequently, upon lines of great importance, 
where the higher velocities must be maintained in winter as well 
as summer, the grade should approximate as nearly to a level as 
practicable. Notwithstanding which, it is now believed that loco- 
motive engines may be used on slopes of from 60 to 90 or 100 feet 
in the mile with greater advantages than was obtained from the 
fixed engines and inclined planes formerly employed. 

1223. It may perhaps be expected that we should give some 
description of the improved form and construction of the locomo- 
tive engines above referred to; but the particular construction of 
steam-engines, mills and other machines, although a branch of the 
engineering profession, is one that is seldom attended to person- 
ally by the Civil Engineer, as he generally leaves the executive 
department to machinists, engineers and millwrights, who have 
regular workshops and devote themselves exclusively to the con- 
struction of such machines as he may order. To enter into such 
a minute description as would be useful to such persons, would 
occupy as many, if not more pages and plates than are contained 
in the present volume, on which account we must pass them over 
in silence. Should the public demand it, the author may proba- 
bly be induced at some future time to publish a separate volume 
founded on his own experience of these practical subjects, but 
for the present we can only refer the reader to Nicholas Wood's 
Practical Treatise on Rail-roads, in which the older locomo- 
tive engines are described, or to the translation of a practical 
treatise on locomotive engines by the Chevalier F. M. G. de Pam- 
bour, 1836, in which their modern improvements to that date are 

* See report of J. Knight, Esq., chief Engineer of the Baltimore and Ohio rail- 
road, appended to the tenth annual report of the president and directors of that 
company to the stockholders, October 7, 183G. 



ON RIVER IMPROVEMENTS. 691 

detailed. Valuable particulars of many other engines and ma- 
chines will be found in Dr. Olinthus Gregory's Treatise on Me- 
chanics, 3 vols.; and in Nicholson's Operative Mechanic; several of 
which works, it is believed, have been reprinted by Carey & 
Hart of Philadelphia. 

Section IL — Of Internal JVavigation. 

1224. Next to roads and rail-roads, the object to which the 
attention of the Civil Engineer is most frequently called in this 
country, is the construction of navigable canals, or rendering 
natural rivers navigable. The question is frequently asked by 
those who have not considered the subject, why should artificial 
canals be constructed at great expense, in countries abounding 
with natural rivers? and why should not such ready formed water- 
courses be made available to the purposes of internal navigation? 
The reasons when investigated are sufficiently obvious. Rivers 
are the natural drains of a country for carrying off its superfluous 
water to the sea, which is the lowest level upon the earth, and 
to answer this purpose they must be inclined, so that their waters 
may descend. They therefore run through a continually de- 
scending line of country without any regard to a right-lined direc- 
tion, and their courses are therefore constantly tortuous or 
crooked, while the water that flows in them runs constantly in 
the same direction, thus offering two obstacles to navigation, first 
by the distance between one place and another being increased 
by the bending of the stream; and secondly, as the stream always 
runs downwards, (except when rivers approach so near to the 
sea as to feel the effects of tides,) it will promote the passage of 
vessels in that direction, but will oppose considerable resistance to 
their moving in the opposite one. In addition to this, all rivers 
are more or less subject to freshets or floods, and the natural in- 
clination is frequently so great as to cause the water to run oflT, 
and become so shallow as to be incapable of floating a boat for 
any long distance. Rivers likewise are seldom of the same width 
throughout, so that in narrow places violent torrents may form 
that would be dangerous to pass in one direction, and could not 
be passed in another during full water seasons. They also con- 
tain slopes or falls, with rocky and dangerous bottoms, and manv 
other impediments to navigation that might be enumerated. The 
consequence is that it is frequently more troublesome and expen- 
sive to put a natural river into a good state for navigation, than 
it is to excavate and construct an artificial canal which shall be 
free from such objections; because in navigable canals the width 
and depth are uniform, and suited to the purposes required. The 




692 INTERNAL NAVIGATION. 

water is quite level and without current, consequently equally 
well suited to the passage of vessels in either direction. The line 
is made as straight and short as possible between the places of 
shipment and delivery, and a canal to be perfect should contain 
an equal, or at any rate an available quantity of water at all 
seasons of the year. Canals are therefore obviously more gene- 
rally useful than rivers, unless they happen to be free from these 
natural obstructions, and then of course rivers are better than 
canals, as being generally more deep and wide, thus accommodat- 
ing large vessels in greater numbers, and this generally applies 
to tide rivers where the current changes its direction twice in 
every night and day. 

1225. The engineering operations for improving the navigation 
of such natural rivers as contain obstacles, consist in forming 
canals across necks of land, to cut off circuitous bends and form 
better and nearer connexions between the straighter parts of the 
stream. Cutting away and widening the banks or shores of nar- 
row places, and cutting away timber or sharp rocks that might 
he dangerous to vessels, and deepening the shallow places by the 
dredging machine, (1135,) or other convenient means. These 
several operations by diminishing the resistance to the motion of 
the water and increasing the inclination of the bed, (which is the 
natural consequence of shortening the stream between any two 
given points,) will permit the surplus water of floods to escape 
more easily, but will be productive of the evil of making the river 
more liable to drought or shallows in short water seasons, conse- 
quently these alterations almost constantly require to be followed 
up by the introduction of dams or weirs and locks. 

1226. A dam is a permanent obstacle to the passage of water, 
except over its top surface, and is built transversely across a river 
for the purpose of keeping back the necessary depth of water 
above it. The surface of the water which before had one gene- 
ral slope or inclination, is now rendered more level, and as this 
nearly level line will intersect the general slope of the river at 
some point behind the dam, another dam will be then necessary 
for the similar purpose of maintaining depth in the reach behind 
it. A river is thus converted, as it were, into a kind of staircase 
or series of nearly level reaches, each of which must contain water 
enough to float craft within itself whenever the general supply 
of water is such as to reach the tops of the dams; and whenever 
there is a greater quantity, the surplus will run over their level 
top surfaces. The connection between one reach and another 
is made by means of a lock, to be hereafter described, one of 
which must be constructed in, or form a part of each dam. 

1227. A weir is likewise a consitruction formed across a stream 



ON RIVER IMPROVEMENTS. 693 

and is similar in its purpose and effect to a dam, but is moveable 
instead of a fixed and permanent obstacle to the passage of the 
water, or one which can be put up and taken away at pleasure. 
It consists of a strong timber framing of long piles driven into the 
bed of the stream, so that their tops may project considerably 
above the greatest height the water can rise to, with diagonal 
braces to resist the weight of the water. Horizontal transverse 
beams are framed into the upright piles to support a set of pad- 
dles or shuttles, each about 10 or 12 inches wide, and jointed or 
planed flat; they are placed close together quite across the stream, 
their length being such as to reach to, and abut against a hori- 
zontal sill of timber laid entirely across the bottom of the river, 
and another line of timber nearer to, or above the surface, while 
their tops extend to such height as may be necessary for penning 
up the necessary depth of water. Each shuttle has a separate 
handle projecting upwards, to be taken hold of for placing or re- 
moving it. The weir requires a lock for the passage of vessels 
as well as the dam, and their operation on the depth of the river 
is the same; but the weir is better suited to streams that are sub- 
ject to great and sudden freshets; because in summer or short 
water time, the whole weir is kept close or shut to retain as much 
water as possible; but in winter and floody seasons, any number 
of shuttles, or the whole of them may be taken up by means of a 
stage constructed for the purpose, and a barge to contain them, 
so that the whole area of the river, or any required part of it, can 
be opened for the passage of the water within a single hour. The 
river Thames in England, remarkable for the immense traffic that 
is carried on upon it, is very subject to heavy floods as well as to 
short water; but its navigation is constantly preserved through all 
seasons by about twenty of these weirs and locks built at conve- 
nient intervals between Richmond and Oxford, beyond which the 
navigation is continued by canal work. These weirs are kept 
close during summer, but are taken up in the fall and during 
winter, when there is no scarcity of water, and the navigation 
can be carried on through the weir, instead of the more tedious 
passage of the lock; and when the dry season approaches, the 
necessary height of water is maintained by putting down as many 
of the shuttles as may be necessary. 

1228. On the subject of navigable canal formation, little can be 
added to what has been mentioned in the preceding chapters. 
The same survey of country, levelling, map and section, will be 
required as for a road or rail-road; but in selecting the line, the 
lowest instead of the highest land must be preferred, so as to avoid 
the expense and other inconveniences of deep cutting, and to in- 
sure a plentiful supply of water at all seasons. While a road 



694 INTERNAL NAVIGATION. 

should be located above or out of the reach of flood water, a canal 
on the contrary must be placed so low that the intended surface 
of its water shall be level with that of the river or stream that is 
to supply it, because water will not rise above its level, unless 
when forced to do so by the exertion of some expensive mechani- 
cal force. This constitutes the chief difficulty in locating or set- 
ting out a canal, because, notwithstanding it must be kept low, 
for the reason just stated, its side embankments must be so high 
as to be constantly above the flood water to which most rivers 
are subject. The effects of floods or freshets require to be most 
cautiously guarded against in canal work, for no earth work will 
stand against a rush of water over its top. If, therefore, a canal 
should be so located as to permit flood water to pass over it, there 
would be little doubt of its being destroyed; while, on the contrary, 
if the water rises to within an inch even of the top of the banks, 
but cannot get over them, it will be safe. On this account canals 
in low positions are frequently made much deeper and wider than 
necessary, for the mere purpose of obtaining a sufficient quantity 
of soil to raise the side embankments above the greatest possible 
height to which a flood water can rise; and this precaution must 
ever he held in mind as the only means of securing and rendering the 
work durable, when executed in positions liable to such accidents. 
1229. The width and depth of a canal must be regulated by 
the size of boats intended to work upon it. To save needless ex- 
pense in cutting, such boats are usually made very narrow and 
very long, which form permits them to carry considerable ton- 
nage, and is rather beneficial than detrimental as they seldom 
have to turn, and expose but a small sectional area to the resist- 
ance of the water when moving. But when a canal has to re- 
ceive vessels from other navigations, its width must be made in 
accordance, and should always be such as to permit two boats to 
pass without contact. A horse towing path, must always be pro- 
vided on the top of one of the side banks, and this from circum- 
stances may be obliged to change from one side to the other, but 
should do so as seldom as possible; and all changes should take 
place at bridges, that the horses may cross the water without 
delay. The bridge arches should be so wide as to permit the tow- 
path to run under them, and they should be high enough to per- 
mit high and light cargoes to pass without obstruction, as well as 
for preventing accidents to persons standing in boats; but the span 
need not exceed what is necessary for the towing path and the 
free passage of one boat. The best form for canal bridges when 
built of brick or stone, is upright piers with an arch that is a seg- 
ment of a circle, as this allows greater headway both for the tow- 
path and cargo than the semicircular arch, although this last is 



OF NAVIGABLE CANALS. 695 

very commonly used. The draw and swing bridge (576 and 578), 
are frequently placed over canals instead of permanent bridges. 

1230. Whenever a canal has to descend from a high to a low 
position, and a plentiful supply of water from a river can be ob- 
tained at its upper end, no difficulty attends the execution. The 
descent or fall from one end to the other being ascertained, will 
determine the number of locks to be used; for the fall in each of 
these should, for obvious reasons, be equal, and should not, if pos- 
sible, exceed six or eight feet to the lock; for if deeper, too great 
a strain is thrown upon the gates and other work by the lateral 
pressure of the water, and the time occupied in passing them will 
be unnecessarily prolonged. The contents of the locks should be 
equal, in order that the water discharged from an upper one may 
be just sufficient to fill those below without surplus, which would 
run to waste. 

1231. As such canals are constantly descending by steps at 
each lock, it frequently happens that a lower reach of a canal 
may fall upon the same level as a lower part of its river of supply, 
or some other stream or rivulet near it, or it may be made to do 
so by a suitable quantity descendine; in its locks, and if so, water 
may be taken into it below as well as in the highest reach, by 
cutting a ditch or canal of communication between such river and 
the particular reach of the canal, and such communications are 
caWed feeders. All canals receive their water by feeders, which 
are level cuts, sometimes of miles in length; while at others, the 
canal itself runs into and joins the river, a part of which is fre- 
quently used instead of a canal, provided it is free from impedi- 
ments and not subject to much variation in the height of its 
water. 

1232. In order to maintain the water at one uniform height in 
canals, or rather to prevent its exceeding the maximum limited 
height, and thus prevent its overflowing the side banks, each 
reach of a canal should be provided with at least one safety dam 
or tumbling bay, which is a strong construction of stone, brick, or 
timber, formed in the side bank in a substantial water-tight man- 
ner, having a level top or surface that accords in height, and 
level with the highest surface the water is intended to have. 
This level must be some inches below the general level of the 
banks; consequently, if the canal should at any time receive too 
much water, it will not be retained above the top of the tumbling 
bay, but will discharge itself and run to waste. Of course, over- 
falls or tumbling bays must be placed in such positions that the 
waste water may be delivered into a river or some water course 
capable of taking it away without harm or destruction to any use- 
ful part of the work. Feeding rivers ought, when possible, to have 



696 INTERNAL NAVIGATION. 

thesame kind of over-falls, in order that they may be unable to 
send a greater height of water into the canal than may be bene- 
ficial to its operations. Feeding ditches if deep, should also have 
dams across their ends that communicate with the canals, and 
these should be built level with the lowest water that will render 
the canal available. By this precaution, the water can never 
run out of the canal into the feeding stream if it becomes low, 
and it will always furnish water when it contains more than their 
height. When canals receive additional feeding streams in their 
lower reaches, the lower locks may be made deeper than the 
upper ones if necessary, without detriment. 

1233. Notwithstanding the total fall of a canal that is fed from 
its upper part only, should be equally divided among its locks, yet 
it does not follow that the locks should be at equal distances from 
each other. It may happen that a country will admit of a per- 
fectly level line of canal for miles, and then may fall suddenly so 
as to require several locks which would accordingly be placed 
close together. Locks, therefore, are distributed into those parts 
of the line which stand in need of them, and where, from the 
natural declivity of the country, they can be executed with the 
least excavation and expense, and especially in such manner as 
not to involve the next reach below them in the heavy expense 
of deep cutting. 

1234. The lock so often referred to, is an ingenious contrivance 
for floating vessels from one level to another without any other 
mechanical aid than the flow of the water itself. It consists of a 
chamber with upright parallel sides, and a bottom which forms 
part of the canal. Its length must be greater than that of the 
longest vessel that has to pass through it, its width is usually suf- 
ficient to contain two such vessels lying close and parallel to each 
other, and its depth must be equal to the difference in level of 
the upper and lower reaches of the canal, in addition to such 
depth of water as may be capable of floating the vessels when in 
their lowest position. The action of the lock depends on the 
established fact, that when two quantities of water communicate 
with each other, they will rise or fall to one common level, and 
its operation will be seen by inspecting Fig. 272, PI. IX, (the 
frontispiece) which is a longitudinal section, and 273, which is a 
ground plan of a lock. In Fig. 272, let the dotted line a be the 
surface of the water in the upper reach of the canal, and b that 
of the water in the lower reach, c c c the coping or top of the 
wall forming one side of the lock chamber, g the bottom of the 
lock level with, or in about the same line as the bottom of the 
lower reach of the canal, i the bottom of the upper reach, both 
which are paved or boarded, and e and/ two pair of gat^s which 



CONSTRUCTION OF NAVIGABLE CANALS. 697 

shut in a water tight manner, so as to confine any quantity of 
water that may be admitted into the chamber formed by them 
and the side walls and bottom. Each pair of gates contains a 
shuttle or valve h, which can be opened from above by a rack 
and pinion /r, for permitting water to pass through the gates while 
closed. Things being thus arranged, suppose that a barge is float- 
ing on the surface of the upper water at a, and has to be lowered 
and passed into the lower reach h. The gates at e andy being both 
closed, the shuttles of the upper gates e must be opened, when 
water will pass through them from the upper reach into the 
chamber, and will soon elevate the surface 6 of the water within 
the chamber to the same level as that at a, and when this is done 
there will be an equal pressure of water both before and behind 
the gates e; consequently they can be opened by their balance 
beams n I, also shewn in Fig. 194, PI. VI. (969,) and the barge 
can be floated from a into the chamber of the lock. The upper 
gates € with their shuttles, must now be closed again, and that 
done, the shuttles in the lower gatesy* mustbe opened, which will 
permit the water before contined in the chamber of the lock to 
flow out into the lower reach, thereby bringing down the surface 
of the water within the lock, and the boats floating upon it to its 
former level 6, which is even with the surface of the water in the 
lower reach. There will now be an equality of height in the 
water before and behind the lower gates, so that they in turn can 
be opened and the barge floated into the lower reach. If, on the 
contrary, it is desired to raise a barge from the lower to the upper 
reach, the lower gates must be open — the vessel must float into 
the chamber — the lower gates and their shuttles must be closed — 
and now the shuttles of the upper gates are opened to fill the 
chamber with water and raise the vessel to the height of the 
upper reach, when the upper gates are opened, and the vessel 
proceeds. 

1235. Whether a barge is raised or lowered through a lock it 
thus appears that the quantity of water necessary for the opera- 
tion must be taken from the upper reach, and is never restored 
to it again, which is a reason for making the chambers as small 
as possible, consistently with the safety of the inclosed vessel or 
vessels; for if a lock is worked without any barge in it, the entire 
quantity of water necessary for tilling the chamber must be let 
down, but if a barge or vessel very nearly occupies the capacity 
of the lock, it will hold the place of the water and the loss will 
be comparatively small. The great diflSculty in general to be 
contended with in canals is want of water, especially if the feed- 
ing stream is occupied by water mills, and of course every pre- 
caution should be used to economize its useless expenditure. In 
88 



698 INLAND NAVIGATION. 

large and deep locks a culvert of brick-work closed by a sluice at 
its upper end, is used to convey the water from the upper to the 
lower reach, as shown at m n m, Fig. 272. This culvert or iron 
pipe is constructed or built in the exterior brick-work, and pre- 
vents the splashing of water that attends the use of the upper 
gate sluice, whenever its position is above the water in the lower 
reach, which is the case in the drawing. 

1236. The building a good, sound and durable lock is considered 
a nice operation, for it is attended with several difficulties, such 
as the difference in level between the two reaches of canal, 
which always produces a tendency in the water to percolate 
and insinuate itself behind the side walls and .under the bottom, 
by which the soil is sometimes washed away and the work un- 
dermined. The unequal pressures to which the work is subject 
from the chamber of the lock being alternately full of water, and 
empty, the heavy pressure, and absence of any pressure at all 
alternately upon the gates, and particularly the lower pair, and 
the lateral pressure of the soil against the side walls, constantly 
pressing them inwards, together with the careless manner in whiels 
the heavy gates are often run together, with a head of water 
upon them producing great concussion constitute altogether an 
irregularity of force and pressure that it is difficult to guard 
against. 

1237. The locks and weirs on the river Thames, between Lon- 
don and Oxford, before referred to, are under the care of, and are 
built and repaired by, the corporation of the city of London, who 
spare no pains or expense to make them as perfect as possible, 
and yet they are made wholly of timber strengthened by iron, 
which material, notwithstanding its liability to decay, is said on 
the experience of the city Engineers and surveyors to be the best 
and cheapest, on account of its being tough and more capable of 
withstanding the shocks and blows the work receives from the 
large and heavy craft that navigate the river, as well as the 
effects of floating ice in winter, and the locks are maintained by 
a tonnage toll paid by every vessel on passing them. In the Lon- 
don and West and East India docks, in which the locks are all 
capacious enough for large ships to pass through them, they are 
made of bricks with stone angles, copings and defending strings; 
and in the generality of canals the locks are of brick-work, with 
some parts of stone. 

1238. In general the bottom of a lock may be laid with good 
sound timber upon piles, because this part is constantly covered 
with water. Short piles are therefore driven over the whole 
bottom at proper distances to support longitudinal sleepers, which 
arc again crossed by transverse pieces, so as to form a grilliage, 



OP CANAL LOCKS. 699 

which is trenailed down upon the pile heads previously cut level. 
All the spaces between the gating must now be carefully pud- 
died, unless that operation has been done before the grilliage is 
laid. The whole bottom is then covered with 2j or 3 inch plank, 
running lengthwise of the chamber. If the lock has to be finished 
in timber, vertical piles may next be driven at about two feet 
apart, to form the side walls, and these should terminate in a 
horizontal capping piece of timber running the whole length of 
the lock on both sides, and taking hold of all the piles by being 
halved into, or morticed upon them. The top or capping piece, 
or every third or fourth pile under it should, moreover, be secured 
by land ties, which are generally formed of whole round timber of 
from 12 to 20 feet in length, according to the nature of the soil, 
disposed as shown in Fig. 273, in which a is the stick of round tim- 
ber so halved, dove-tailed or otherwise fixed to the vertical piles 
or to their capping piece, as to be incapable of drawing or giving 
way. The outer end of this piece is similarly doi^e-tailed or 
halved on to another but shorter stick of whole timber c, and im- 
mediately within this two piles d d, are driven into the ground, 
which should be in contact with the piece c, or else wedges must 
be driven between it and the piles, so as to render it impossible 
for the side walls of the lock to incline inwards without carrying 
the piece c, the piles d d, and a large quantity of solid ground with 
them. In using land ties, the piece a usually inclines downwards, 
so that its outer end, and the piece c, together with the piles, 
may be all covered with earth, so that no part of the tie appears 
out of the ground when the w^ork is finished except the end that 
joins the side of the lock, and this ev^en is frequently concealed in 
timber locks, and is constantly so in those of brick or stone, be- 
cause in these materials the tie is connected to the wall by an- 
other transverse piece of timber b, which is built into the centre 
of the wall. The vertical piles to form the sides having been 
driven so as to range perfectly with each other, are planked with 
stout plank on the inside faces, or inside of the lock chamber, and 
the side walls when finished should be vertical, or very slightly 
battered back, and perfectly right-lined and smooth from one end 
to the other, with the exception of two recesses on each side 
marked x x in Fig. 273, which are to contain the gates when they 
are open; consequently their depth and extent must be governed 
by the thickness and radius of the gates. The object of these 
recesses is that when the gates are open the whole inside of the 
lock may be flat and smooth, and free from all projections that 
vessels might strike against, and thereby injure themselves or the 
lock. As, however, locks are always much narrower than the 
canals of which they form a part, their extreme ends must splay 



700 INLAND NAVIGATION. 

or open to the full width of the canal, and even some distance be- 
yond it; and this is effected by forming oblique wing-walls which 
may be curved as at g g at the left hand end of the figure, or 
right lined, as at g g on its right hand end. 

1239. The parts of a lock are the same whether it is built in 
timber, bricks, or stone, and having stated how a lock may be 
partly constructed in timber, we shall next state how it may be 
formed with other materials. In brick and stone locks it is not 
uncommon to make the floor or bottom of timber, but such tim- 
ber should always be supported upon piles, unless the lock is built 
in stiff clay, or soil that will offer effectual resistance to the pass- 
age of water. Sleepers or joists will be necessary whether piles 
are used or not, because the flooring planks must be spiked or 
trenailed down to them. If joists only are used they must be 
placed transversely, that their two ends may work into the side 
walls for holding them securely in their places; and whether the 
bottom is formed of timber, bricks, or any other materials, the 
greatest care must be taken to render it impervious to the pass- 
age of water under the work by puddling, brick-work laid in 
cement grout, or beton, because there will be a considerable 
head or difference of level in the water to guard against in every 
lock; and if the upper water finds a passage behind or under the 
work, be it ever so small in the first instance, it will gradually 
enlarge, and there will be danger of the earth washing away, 
and the lock blowing up. Should the soil be stiff clay, a flat bot- 
tom of brick-work or masonry may be laid all over it, as shown 
in Fig. 272 by t t, and if bricks are used the safest and strongest 
mode is to work the upper or finishing course with bricks on end 
laid in cement. Should the soil be of a less trustworthy charac- 
ter, the bottom will be better if formed by an inverted arch, 
which may be either semicircular or semielliptic, the last form 
being adopted when from wetness of soil or other causes it may 
not be possible to sink deep enough into the ground to build a 
semicircular invert. The side walls of the lock chamber may 
stand upon the spring of this invert, but when the bottom is flat, 
these walls are built like all others, from a level foundation 
trench, piled and planked or not as may be necessary, but always 
commencing some inches below the extreme foundation of the 
bottom, and oversailing, or standing upon it for a half brick in 
thickness when it arrives at the upper level, to assist in keeping 
the floor or bottom down in its place. The side walls, though 
perfectly smooth within the chamber, should be built with but- 
tresses or counterforts on the sides next the land, as shown at y y, 
to give them additional strength; to assist in which a land tie, such 



OF CANAL LOCKS. 701 

as already described, is also introduced near the top of every but- 
tress, on both sides, in the manner shewn in the figure at a b c d. 
1240. The lock gates are shown in plan in their real position, 
when shut by e e, which are called the upper, and f f the lower 
gates in Figs. 272, and in elevation in Fig. 273, and a front view of 
one of them is given at Fig. 194of Fl. VI., already described (9G9,) 
to show the particular construction, such figure being an upper or 
short gate. The height of the upper gates must be such as will 
extend from the upper surface of the paved or planked bottom i 
of the upper reach. Fig. 272, to the extreme top surface of the 
water contained in that reach, while the lower gates f are about 
twice as high, or extend from the paved bottom of the lower 
reach d, to the full water level of the upper reach. These gates 
each consist of two strong vertical posts of oak or other strong 
timber e and/. Fig. 194, united together by the requisite number 
of horizontal timbers g g g o( the same size, and then planked 
over diagonally, as at m, m; or sometimes the planks are fixed 
vertically, and one strong diagonal timber brace or strut in sepa- 
rate pieces is let in between the horizontal beams. The hori- 
zontal beams are not at equal distances from each other, but are 
put closer together near the bottom of each gate, because the 
pressure of water increases as its vertical height, consequently 
gates require to be much stronger near their bottoms than at their 
tops. This is shown in the figure. These beams are morticed 
into the vertical ones, and further secured by what are called T 
and L plates of iron, let in flush with the surface of the timber 
and firmly spiked to it in the positions shown in Fig. 194. The 
vertical posts e and f are formed of square timber, but the outer 
side of e is cut into a bevil form in order that it may meet and 
make a flat, smooth, and water-tight joint, called a mitre, with 
the similar post of the opposite gate, when both are placed in 
their proper angular positions in the lock and are shut, on which 
account these posts are called mitre or shutting posts. The nature 
of the joint they form is shown at n, n. Fig. 273. The other post 
f, Fig. 194, is called the quoin or hanging post. Its outer side is 
worked into the form of a segment of a circle, upon which the 
gate turns or rolls in a vertical curved cavity made to fit it, and 
called the hollow quoins of the lock. In brick locks the hollow 
quoins are always worked out of large free stones set in their 
proper places in the brick-work, as shown at z z z z in Fig. 273; 
but in timber locks they are frequently hollowed out of very large 
sticks of timber, or are occasionally made of cast iron with 
flanches or projections by which they may be fastened to the 
wood. At all events they must fit the quoin posts of the gates 
when shut so accurately as to permit little or no water to pass 



702 INLAND NAVIGATION. 

between them; and they are so fixed in the work of the sides of 
the chamber, that when the gates are quite open they will fall 
back into the recesses x x, without leaving the hollow quoins, and 
thus produce one even, smooth, and uninterrupted surface on the 
insides of the lock chamber. The gates are not hung by hinges, 
because it is necessary they should have some play, or freedom of 
motion by which they are permitted to adjust themselves into a 
water-tight position when the pressure of water comes upon them. 
They are therefore fixed by an iron gudgeon or pivot i let into 
the lower end of each quoin post, and which is received into a 
cast iron step or pivot hole fixed in the floor of the lock. The 
hole in this step is not cylindrical, but oval, so that the motion of 
the quoin post shall not be confined to a fixed axis, but may shaft 
an inch or more to allow for the mutual wearing away of the 
quoin post and hollow quoin by use, thus maintaining a tight joint 
for many years. The upper end of the quoin post is held by a 
small part of its top, above the gate, being made cylindrical, and 
this part is embraced by a flat iron strap h passing round it. 
This strap is in two pieces, one of which has long tails with cork- 
ings that are secured by lead or otherwise to the top of the up- 
per stone or material of the hollow quoin, and the other piece is 
semicircular, but with long ends, fitting on to the fixed part, and 
attached to it by an iron gib and wedges, so that it can be moved 
at any time for taking out the gates, or can be adjusted so as to 
produce any requisite pressure between the quoin post and hol- 
low quoin at pleasure. The great weight of the gates, and par- 
ticularly of the lower pair, which are never covered by water on 
both sides, would cause them to sag or droop, and consequently 
to rub against the floor of the lock so as to render them very diffi- 
cult to open; and would also injure their water-tight joints, if 
some expedient was not resorted to for preventing this effect. In 
the first place the planking is put on diagonally, as shown at m 
m. Fig. 194, or a strong diagonal strut is used, or both may be 
used conjointly, and secondly, the heavy balance lever n 1, Figs. 
194 and 273, is morticed into the mitre post, and upon the top of 
the quoin post, and the weight of its end 1 (which, by its length, 
also forms a powerful lever for opening and shutting the gates,) 
should be such as will exactly balance that of the gates when the 
highest head of water is upon them, thus counteracting any ten- 
dency the gates may have to sink or sag, and causing the moving 
of them for opening or shutting to be comparatively easy. 

1241. When gates are very large, as when they occur in ship- 
ping docks, or ship canals, these balance beams must be very long 
and massive to be eflfectual, and they would not only be unsightly, 
but inconvenient from their long radius. In such locks they are 



OF CANAL LOCKS. 703 

therefore not used, but a strong cast iron wheel or runner is fixed 
in proper framing to one side of each gate, and this runs upon an 
iron rail-road or quarter circle of cast iron fastened upon the floor 
of the lock in the direction shown by dotted lines near x x x x, in 
Fig. 273, and these wheels answer the purpose of preventing the 
gates from sagging, while they diminish the friction of their mo- 
tion. When gates are thus constructed they are opened and shut 
by chains attached to their lower parts, and these chains extend 
to, and coil round, a vertical shaft, the top of which terminates in 
a capstan that stands above ground, and is turned by handspikes 
or levers applied into its holes whenever the gates have to be 
moved. The capstan reaches to the full depth of the lock, and 
works in a cylindrical shaft or well, lined with brick-work, and is 
covered over on its top. These capstan wells are constructed in 
the brick- work of the sides of the lock, and are generally four in 
number for each pair of gates, two being placed on each side, one 
for opening the gate nearest to it, and the other for shutting the 
gate on the^ opposite side. The chains pass through iron pipes 
built in the side walls and making communications between the 
chamber of the lock and the wells, and the water of course enters 
these wells and stands at the same height in them as in the part 
of the lock to which they open. 

1242. From the nature of lock gates, it will be apparent that 
they cannot be brought into contact with the bottom of that part 
of the lock in which they work, without producing such friction 
as would render them incapable of motion without great force, 
particularly as the bottom of every lock chamber becomes a de- 
pository for that quantity of mud and silt which will always flow 
more or less from the upper reach. The bottom of the gates 
must therefore be kept from one to three inches, according to the 
nature of the soil, and its being more or less stony above the floor 
of the lock; consequently no water-tight joint can be made be- 
tween that floor and the bottom of the gates. This joint is there- 
fore produced by a framing of timber called the mitre sill of the 
lock, which not only forms the necessary water-tight joints, but 
aflfords very useful and effectual support to the 'gates against the 
pressure of water to which they are subjected. The mitre sill 
has an appearance similar to the framed principal or truss of a 
roof. Its form in plan is shown at q in Fig. 273, which is the 
mitre sill of the upper gates, and at r, which is that of the lower 
gates, and the same letters of reference indicate the same parts 
in the longitudinal section Fig. 272, in which last figure it will be 
perceived that although the major part of the mitre sill stands or 
projects above the surface of the floor of the lock, yet that a part 



704 INLAND NAVIGATION. 

of it is let into, oris below that surface, to give it greater strength 
and render it more water-tight. 

1243. The mitre sill consists of four strong pieces of timber, 
one of which is a tie beam running transversely across the Jock, 
and being so long that its two ends may work into the side walls 
under the hollow quoins. Two others are in the nature of princi- 
pal rafters which meet in a point in the centre, and tenon into 
the tie beam at their two feet in such manner that they may 
make the same angles as the gates, and be parallel and close to 
them, for on these pieces the water joint depends; and the fourth 
is in the nature of a king post, and joins the meeting of the two 
rafters with the centre of the tie beam, by which the expansive 
tendency of the rafters is in some measure prevented. The 
whole mitre sill being strongly framed together is laid horizon- 
tally in the work, and firmly built in, the interstices between the 
pieces being filled in with brick or small stone work, laid in 
cement. The water-tight joint at the bottom of the lock gates is 
not therefore formed by their bottoms coming into contact with 
the floor of the lock, but by the insides of the lowest horizontal 
beams coming into close contact with the vertical outsides of the 
rafters of the mitre sill, therefore the placing and due adjustment 
of this part of the lock is of the greatest importance; and to pre- 
vent the mitre sill from giving way to the sudden concussions 
that may arise from a careless shutting of the gates, which close 
with great violence, owing to the difference of level of the water 
on the two sides of the gates, the tie beam of the mitre sill is 
partly buried in the solid masonry of the aprons of the lock, some- 
times made wholly of timber upon brick or stone foundations; or 
if the aprons are built wholly of these materials terminated by 
arches, as shown in the plan Fig. 273, in which it will be seen 
that the lower apron extends farther than the upper one, because 
the lower apron from the greater height of its gates requires more 
strength, and maybe continued to any distance without detriment 
to the lock, since this apron is built wholly in the bottom of the 
lower reach of the canal, while the upper apron, if continued, 
would not only pit)ject into the chamber of the lock, and require 
it to be made longer, thereby increasing its expense, but might 
prove dangerous to boats, by one of their ends lodging upon it 
while the water was high and it was concealed by it. To pre- 
vent the occurrence of such accidents to vessels, the upper apron 
is therefore made short, or extends as little into the chamber of 
the lock as possible, and has its edge or arris rounded, as shown 
in the section Fig. 272, so that if the end of a vessel should lodge 
upon it, it will gradually slide off. 

1244. The part of a lock which requires the greatest attention 



OF CANAL LOCKS. 705 

on the part of the Engineer and builder is the dam and upper 
apron, together with the upper wing-walls, because these have to 
sustain the whole head of water due to the fall in the lock, and 
must therefore be made very strong to resist the blows and con- 
cussions of descending boats often carelessly navigated, and must 
also be perfectly water-tight. The dam consists of a solid block 
of brick-work or masonrys, Fig. 272, even though all the rest of 
the lock should be of timber. This must be built of the hardest 
and soundest materials laid in hydraulic mortar or cement, and 
should be supported on piles to prevent the soil under it from be- 
ing washed away or disturbed. The upper wing-walls g g require 
the same attention, and should not only run quite across the full 
width of the canal, but some distance into the dry land on each side 
of it to prevent the possibility of the upper water getting either be- 
hind or through them. The more effectually to prevent this?, 
both the outsides of a lock should be carefully puddled through- 
out its whole extent, whether it be built with timber or masonry, 
and this renders the use of buttresses and land ties the more ne- 
cessary; because all the soil in contact with the lock sides is in 
the first instance in a semifluid state, and vs'ill therefore be more 
likely to cause the sides to cave or incline inwards. It will likewise 
be observed in the plan. Fig. 273, that the lock sides vary in 
strength and thickness, independent of the buttresses, and this is 
because different parts of these sides are exposed to different 
forces. The greatest force, and that which requires the most 
particular care to guard against it, is the tendency to lateral 
spreading in the lock gates from their angular position when shut, 
and this requires that the hollow quoins and the work that sur- 
rounds and supports them should be stronger than any other part 
of the work, particularly in that direction which is the resultant 
of the two forces in action, viz: the tendency of the water to press 
forward in the direction of the lock, and the lateral spread of the 
lock gates which will act in a direction at right angles to it. The 
hollow quoins should therefore be well supported in the descend- 
ing direction of the canal and on their two sides; and next to these 
the wing-walls will require attention from the weight of water 
and concussions to which they are exposed. 

1245. The lateral pressure produced by the head of water on 
the lock gates will vary with the angle the gates make with each 
other, and Engineers are not well agreed as to what this angle 
should be to produce the best effect. If the angle is too acute, 
the head of water will not produce pressure enough to close the 
mitre joint, and drive the quoin posts home into the hollow quoins, 
and the lock cannot be made water-tight; and on the contrary, 
when the angle is too obtuse, so as to let the two gates come 
89 



706 INLAND NAVIGATION. 

nearly into a right line, the pressure becomes so enormous that 
the mitre joints and quoin posts become bruised and maimed, and 
soon give way. The rule which the writer has adopted from his 
own experience, and has found to answer well, is to make the 
angle such that the king post of the mitre sill may be one-fifth of 
the length of the tie beam or width of the lock chamber when the 
head of water to press on the gates amounts to five feet, or any 
height more than that and less than nine feet. When the press- 
ing head is under five feet a more obtuse angle is necessary to 
produce close shutting, and then one-sixth of the width will be 
better. But when the head is very great, as above nine feet, the 
king post may have one-fourth of the width, and will produce 
close joints. 

1246. It is needless to say any thing on the construction of the 
sluices that are formed in gates, and the rack and pinions by 
which they are worked, to open passages for the water from one 
level to another, further than that they are better made of cast 
iron than of wood, because the former material is less liable to 
wear, and to swell and become fixed. A broad plank is usually 
fixed on the convex side of each gate, which not only serves as a 
bridge or scaffold for opening these sluices, but as a foot bridge 
for passing over the canal whenever the gates are shut. A ver- 
tical groove, o, above the upper gates, and a similar one, jo jo, 
below the lower gates, from three to four inches wide, should also 
be worked in stone or sound brick-work in every lock. These 
are called stop plank grooves, and are for the purpose of receiving 
and retaining pieces of three or four inch plank cut to a proper 
length to fit into them, and planed or jointed on their edges so 
that if any repair becomes necessary to the lock, or the gates 
should require to be taken out, this can be done without the loss 
of all the water that is above the lock; because by introducing 
the stop plank, and smearing their joints with clay (if necessary) 
before the gates are taken up, most of the water can be saved. 

1247. When canals have an immense traffic of boats running 
in both directions upon them, double locks are formed to avoid 
delay. That is to say, instead of contracting the canal into the 
width of a lock, and terminating it by wing-walls, two locks 
are built parallel to each other, and close together, being only 
divided by a thick and substantial wall, which thus becomes the 
side in common of them both: one lock is reserved for boats pass- 
ing upwards while the other is kept for those going downwards, 
so that no delay or confusion is occasioned. Such is the construc- 
tion of the locks on the Regent's canal which encompasses the 
whole northern part of London, and unites the Grand Junction 
canal which branches into the northern parts of the island of £ng- 



OF CANAL LOCK.S. 707 

5and with the river Thames below its bridges, and thus opening a 
'direct communication between the shipping port of London and all 
other parts of the country. 

1248. It has been before stated that whenever a canal descends 
regularly from a high to alow position, and has a plentiful feeder 
at its upper extremity, there is little difficulty in its execution. 
But it is frequently necessary to carry a canal over a high ridge 
or an elevated country, and then it is that the skill and investiga- 
tion of the Engineer are called into action. A canal of this de- 
scription differs in no respect, either in its locks or in itself, from 
that already described; but since all locks can only work whether 
the traffic is ascending or descending, by water running from a 
higher reach into the lock, and from thence into the next reach 
below it, it is evident that all the necessary water must be sup- 
plied from the upper reach. Whenever, therefore, a canal has 
to pass over an extent of elevated ground, it must look down- 
wards in each direction from the highest point, because from that 
all the water to work in both directions must be supplied; and the 
difficulty of executing canals of this description arises from the 
general scarcity of water courses, or efficient feeders, in the high 
lands. It frequently happens that a long line of perfectly level 
canal can be formed in elevated positions, but it seldom occurs 
that sufficient feeders can be found there to supply the double 
lockage downwards from each end of this elevated line, which is 
called a summit level. 

The Grand Junction canal before referred to, is of this descrip- 
tion, for it rises gradually from London to near the centre of the 
island, and then falls again in proceeding northwards to Manchester 
and other northern manufacturing districts; and it happens that no 
water can be obtained by natural means to supply its summit level, 
which, therefore, depends on large reservoirs which have been 
excavated to catch rain water, and the power of a large steam 
engine which works pumps and elevates the water of a neighbour- 
ing river, whenever the natural supply becomes insufficient. The 
Regent's canal at London is similarly circumstanced, and is sup- 
plied with water from the river Thames whenever its other 
sources fail. Water thus artificially supplied is always expensive, 
and such means of obtaining it should never be resorted to when 
it can be procured by natural means. 

1249. Before constructing a canal of this description, a nice 
calculation becomes necessary; first to determine as nearly as may 
be, what the quantity of traffic such a canal is likely to have, 
and what income it will yield in the shape of tonnage tolls. 
Against this must be placed the cost and maintenance of pumps, 
and of a steam engine, water-wheel, or horse power to work them. 



708 INLAND NAVIGATION. 

The number of boats expected to pass, and the size of the locks, 
will determine the quantity of water necessary for working such 
a canal; and this being fixed upon will determine the size of the 
pumps, and the number of hours they must work each day to 
yield the supply, from whence its expense will be easily deduced, 
and it may be determined whether such a canal will be profita- 
ble or not. The difijculty, however, is generally confined to the 
upper reach alone; because as the canal descends feeders will 
generally be found to supply its lower reaches, and therefore it 
often happens that notwithstanding a summit level may be attend- 
ed with great loss, yet it is resorted to and constructed for the 
mere purpose of continuing a long line of communication that 
may be profitable at its lower ends, and yet would, perhaps, be 
useless if broken off in its central part; it therefore becomes pro- 
fitable to submit to a small loss for a general good. 

In some instances where a summit level cannot be obtained 
without inordinate expense and inconvenience, the two descend- 
ing canals are united by a rail-road over the intervening high 
land, which continues the line with no other inconvenience than 
the unshipping and reshipping of the goods. 

1250. From the difficulty of obtaining water in summit levels, 
and positions where it is very scarce, the attention of Engineers 
has been turned to the improvement of canal locks, with a view 
to prevent their wasting the full quantity of water they are capa- 
ble of containing every time that a boat is passed. The directors 
of the Regent's canal thought this so valuable a desideratum that 
they oflTered a large reward to any person that would contrive a 
lock v»7hich should waste no water, and a scale of smaller rewards 
for others in proportion as they diminished the loss. This brought 
forward a number of devices of great ingenuity, all of which de- 
pended more or less on the principle of having adjacent reservoirs 
connected by culverts or pipes with the main lock chamber, into 
which solid plungers were introduced, to expel the water into the 
lock chamber when it was required to rise in it, while it was 
made to fall by withdrawing such plunger. The committee 
judged the contrivances of Col. Sir William Congreve and Mr. 
Busby to be the best, but they were all too complicated or diffi- 
cult of execution to be carried into practical etfect, although one 
lock on Sir William Congreve's plan was built. It was very 
costly, and failed from the side walls giving way for want of but- 
tresses or land ties, in consequence of which it had to be taken 
down, and was not rebuilt again. 

1251. Ihe best, most simple, and efiScient lock for saving 
water, was in use antecedent to these new contrivances, and as 
it is simple, and has been tried and found to answer the purpose, 



OF CANAL LOCKS. 709 

we shall describe that alone. It is called the side pound, or pond 
lock. 

This lock differs in no respect from those already described, 
except that it must have a number of ponds or reservoirs of differ- 
ent depths built in water-tight brick-work or other material, as 
near to it as possible, and each of these reservoirs must have a 
pipe of communication with the chamber of the lock, and a sluice 
or penstock for shutting the water communication. The usual 
manner of building these locks has been to place three reservoirs 
on each side of the lock, and of course there must be six sluices 
or penstocks, but we shall only describe three of them, for that 
description will equally apply to any greater or lesser number. 
Looking at the plan, Fig. 273, we may suppose v ti w to be brick 
culverts or iron pipes leading out of the side of the chamber of 
the lock, at three different heights, indicated by the same letters 
in Fig. 272, into three separate reservoirs formed near the side of 
the lock, and that each passage has a sluice by which it may be 
closed. We will further suppose that all the reservoirs are empty, 
and that it is desired to pass a boat from the upper to the lower 
level. The commencement of the operation will be similar to 
that of any common lock; for first, both the upper and lower 
gates of the lock must be closed, unless the water within the 
chamber has been previously let in and stands at the full height 
of the water in the upper level, when the boat may float into the 
chamber; but should this not be the case, the chamber must be 
filled with water from the upper level as usual, before the boat 
can pass into it. The upper gates and their sluices being closed, 
the water must be let out in order to depress the boat, but in- 
stead of opening the sluices in the lower gates and letting the 
water out into the lower level, as before described, the sluice that 
closes the orifice and passage w is opened, and the water passes 
into the highest side reservoir, and continues to do so until the 
water in it attains the same level as that within the chamber of 
the lock; and whenever this occurs, the sluice of w is closed, and 
that of the passage u opened, by which the central reservoir will 
be filled; when u is in like manner closed, and v is opened to per- 
mit the remaining quantity of water to run off. As, however, the 
ori6ce v is placed on a level with the water surface of the lower 
level, it cannot carry off all the water that is necessary, because 
the water in the reservoir rises as much as that in the chamber 
is depressed until the two quantities attain a common level; 
therefore v must be closed as soon as this is effected, and the re- 
maining quantity of water must be run off into the lower level, 
by opening the sluice h in the lower gates, and this last quantity 
of water will be all that will be wasted. In the event of a boat 




710 INLAND NAVIGATION. 

having to be passed wp the canal, the working of the sluices are 
exactly the reverse of what has just been described. The boat 
passes into the lock from below, and the lower gates and their 
sluices being closed, the orifice -o is first opened, when all the 
water contained in its connected reservoir will run back again into 
the chamber of the lock, when -o must be closed, and u opened to 
introduce the water of the central reservoir, u Is then closed and 
w opened to admit the highest water, which will, however, be 
insufficient to fill the chamber of the lock up to the water level. 
This last filling must therefore be obtained by opening the sluices 
in the upper lock gates. The deficiency of water arises from the 
reciprocal rise and fall of the water in the lock and the reser- 
voirs, for whatever may be their size, the water running into 
them can only rise the precise quantity that it falls within the 
lock and vice versa. It follows, therefore, that the superficial 
area of each reservoir should be at least equal to that of the lock 
between its gates, for if less the quantity of water run out would 
be of little avail. For the sake of keeping the description simple, 
we have only spoken of three orifices and three reservoirs on erne 
side of the lock, but four or five can with equal ease be intro- 
duced on each side of the lock, taking care to make their discharg- 
ing orifices on different levels which follow each other at equal 
and regular intervals; and as the saving of water is proportionate 
to the difference in their level, the real loss may be greatly re- 
duced. This modification of lock was contrived by Mr. James 
Playfair of London, and answers the purposeof saving water very 
effectually, but it is, nevertheless, objectionable on account of the 
loss of time required for working it. The rapidity of a flow of 
water is always governed by its perpendicular descent, therefore 
in the common lock, the rush of water on first opening the gate 
sluices is very great, rendering the culvert m n m, Fig. 272, ne- 
cessary, when the difference of level is great; but as the water in 
the chamber reaches the height of either the upper or lower 
levels, its velocity constantly decreases, and at last disappears, thus 
rendering a loss of from seven to ten minutes inevitable in passing 
a boat through a common lock. In the side pound lock just de- 
scribed, especially when it has many reservoirs, the difference of 
level of the water in the chamber, and that of the reservoir that 
is opened to receive it, is always small, and the water conse- 
quently flows slowly and languidly, and with no greater velocity 
from an upper than a lower reservoir, therefore, independently 
of the time necessary for opening and shutting many sluices, the 
operation of this lock must be very slow. 

1252. The only means that has yet been contrived for obtain- 
ing greater celerity of movement, is by plungers, which are large 



OF CANAL LOCKS. 711 

hollow water-tight boxes loaded with stones so as to cause them 
to sink into brick or stone chambers which communicate at their 
bottoms with the chamber of the lock. Their magnitude must 
be such, that when raised up out of the water, they vvill cause 
such a depression in its height as will bring it level with the 
water in the lower reach; while by sinking them, the water is 
protruded into the chamber to a height equal to that of the 
higher reach. These plungers are balanced to diminish their 
effective weight, and are raised and lowered by appropriate ma- 
chinery. The simplest plan of assisting a summit level or canal 
that is likely to suffer for want of water is to construct very 
spacious ponds or reservoirs, when the form of the country will 
permit them, at such elevation that water can be taken from 
them by its natural fall whenever required. Such reservoirs may 
depend on rain water for their supply, and every spring and 
brook that can be made available should be carried into them. 

1253. When canals open a communication between the central 
part of a country and the sea or a large tide river, they com- 
monly terminate in a large basin in which ships and smaller ves- 
sels may ride for loading and unloading without blocking up and 
impeding the river, and such basins when large are called docks, 
or wet docks. Docks must contain sufficient depth of water to 
float the kind of vessels they are intended to contain, and should 
be surrounded by perpendicular, or nearly perpendicular walls 
on all sides, to preserve the banks and permit vessels to come 
close to them. These walls are of brick-work or masonry slightly 
battered on the front, and having offsets, buttresses and land ties 
next the ground side, with strong iron rings for mooring vessels. 
Sometimes the side walls are wholly lined with timber, by driv- 
ing strong piles, and planking them on the front, when the walls 
are said to be campsheeted. When timber is used it should termi- 
nate in a very strong capping piece, and brick-work or masonry 
should finish with a coping formed of massive and heavy stones 
clamped together, in order that they may not be disturbed or 
broken by the heavy loads that come upon them. The ground 
behind the walling frequently requires puddling to render it 
water-tight, and should be made up level with the top of the walls, 
or be rather above them, and be formed into a gentle slope to 
keep it dry. This serves as a wharf for depositing goods for ship- 
ment, or as they are received from ships, and ought to be of con- 
siderable width. Within it, a road should be formed, amply wide 
enough for two carts to pass; and beyond this warehouses, with 
open roofed sheds, may be constructed for depositing goods; and 
if the whole is surrounded by a high wall with two gates, one for 
carriages to pass in, and the other to go out, such an arrrange- 



712 INLAND NAVIGATION. 

ment will be found very convenient for ports of extensive trade, 
as affording great facility for transacting business, and great 
security of property; and such are the London, West and East 
India docks of London, and many others of sinnilar construction in 
different parts of the world. 

1254. To maintain a sufficient height of water in wet docks 
that communicate with tide water, as well as to prevent the ves- 
sels from rising and falling, which is inconvenient in their loading 
and unloading, tide locks are employed. The tide lock is the 
same in principle as the common lock before described, ex- 
cept that only one pair of gates are necessary, although two are 
frequently used. The gates must of course be large enough to 
permit the passage of all such vessels as are to be admitted into 
the dock; and when a single pair of gates is adopted their salient 
angle points inwards or towards the dock. The gatCvS are opened 
to permit the entrance of the tide water as it rises, but are shut 
as soon as it reaches its greatest height; consequently when the 
tide water of the river or sea recedes or falls, the full high water 
elevation is maintained within the dock or basin, but of course 
the single pair of gates cannot be opened under this head of water, 
and no vessel can pass in or out until high water occurs again; 
and then the water on the outside being of the same height as 
that within, or nearly so, the gates may be left open for the pass- 
age of vessels. As this occurs twice in every twenty-five hours, 
it occasions no inconvenience. Large docks should have two 
locks, in different positions, in order that a line of vessels may enter 
by one, while another passes out by the other without interfering 
with each other. And the gates must have sluices or side cul- 
verts through the walls, because the height of tides vary at the 
same place with different times and seasons. If the external tide 
water rises higher than the confined dock water, it will force 
open the gates and gain the same level without any artificial 
assistance; but should the external water be less elevated than 
that within the dock, the preponderance of force within might pre- 
vent the opening of the gates when required, and in that event 
the sluices must be opened, and so much of the inclosed water be 
permitted to run out, as will produce the necessary equality of 
level. 

1255. Mr. Fulton, to whom the world is indebted for the first 
practical application of steam to the purposes of navigation by the 
formation of steam-boats, proposed the introduction of dry in- 
clined planes as a means of transferring loaded boats from one 
level to another, when the difference was too great to be accom- 
plished without several locks and great expense; and several of 
them have been executed, and employed in Great Britain with 



OF CANAL LOCKS. 713 

success. Mr. Fulton published a separate work on this subject, 
illustrated with plates showing the necessary details for carrying 
his plans into effect. The inclined plane is an iron rail-road pro- 
jecting some distance into the canal, and the carriage, called a 
cradle, that runs upon it, has wheels, and is formed to tit the bot- 
tom of the boat, and being lowered upon the inclined rail-road 
beneath the surface of the water the boat is passed into it, and 
secured by proper iron fastenings when the rope or chain of the 
carriage is drawn up by a steam engine or horse-power capstan 
placed at the top of the inclined plane. The rail-road proceeds 
in a similar manner some distance into the upper reach of the 
canal, into which the cradle and boat must be lowered until the 
water is deep enough to float the boat. Boats are raised and 
lowered in this manner upon inclined planes which rise from 
one to two hundred feet at once, but of course this mode of trans- 
ference is more liable to accidents than when locks are used; but 
saves something in time, and much in the expense of building 
locks. 

1256. In the formation of canals, they sometimes have to cross 
deep vallies or rivers, and not unfrequently streams or rivers 
which may even be navigable. The piling up or embankment 
of earth would be impossible in this latter case, and in the former 
one there might be a difficulty in procuring the necessary quan- 
tity of soil, and if it could be procured, its removal would be 
attended with very heavy expense. The canal will therefore be 
more economically and better continued by an aqueduct^ which is 
a bridge composed of timber or stone piers, but instead of being 
covered by a roadway, it is formed into a duct or trough wide and 
deep enough to float any boat that can navigate the canal of 
which it forms a part. 

All that has been said upon bridge building of course applies to 
the formation of aqueducts, and in addition to that, it may be 
observed, that great care is necessary in the formation of the 
water-course to prevent its leaking. Aqueducts are sometimes 
made wholly of brick or stone, sometimes wholly of timber, and 
occasionally of either of the above materials, but with the water 
channel composed of cast iron plates, put together by flanches 
with screw bolts and nuts, so as to produce permanently water- 
tight joints. If the piers or supporting posts are of timber the 
aqueduct or water channel should be of timber also, because such 
supporters will be liable to decay, to warp and to change dimen- 
sions; therefore perfectly inflexible materials, such as brick or 
stone-work ought not to be placed upon them. In forming timber 
aqueducts, the transverse beams that support the floor must pro- 
ject on each side to a distance fully equal to the depth of the 
90 



714 INLAND NAVIGATION. 

water trunk, (which need never exceed four feet,) in order that 
oblique braces or struts may be introduced to maintain the per- 
pendicular timbers to which the inside planking is nailed in their 
proper upright positions. The bottoms of these upright pieces 
may mortice into the transverse beams, while their tops are let 
into a string of large whole square timber running the whole ex- 
tent of the aqueduct, and projecting a few inches over its inside, 
to protect the planked sides from being injured by boats striking 
against them in their passage. The projecting ends of the bear- 
ers also serve to support the floor of a horse towing path on each 
side of the water trunk, which should be placed at least a foot 
below the projecting side sills, to prevent horses slipping into the 
trough; and the two outsides of the towing path should be 
protected by railing so framed as to assist in supporting the path, 
which is first planked longitudinally, and afterwards covered with 
short transverse planks, to be moved or repaired as they wear out. 

1257. The best and most substantial method of building an 
aqueduct, (when expense is not an object,) is to form it, piers 
and all, of masonry or brick-work, with elliptic or segmental 
arches, worked up to a perfectly flat surface on the upper side, 
upon which the side walls of the channel are afterwards erected. 
In brick or stone aqueducts clay puddling cannot be resorted to, 
because the construction should not be such as will allow the 
puddle to be kept constantly moist, without which it will not con- 
tinue water-tight. The retention of water must therefore depend 
entirely upon the soundness of the work, and the materials used 
must consequently be the very soundest bricks, or stone, that can 
be procured, laid or built wholly in good hydraulic cement, which 
must be made thin, and worked in close but full joints. The 
bricks may be rendered more impervious to water, by dipping 
each of them as used in liquid cement, and by grouting the work 
at every second course, and after it is finished by plastering the 
surface to at least half an inch thick with Roman cement and 
clean sharp sand. The brick-work should also be three bricks 
thick to enable it to resist percolation, and withstand the pressure 
of the water; and to promote these effects, the side walls should 
have narrow off*sets or footings of about two inches wide in every 
second course, on both sides, for eighteen inches or two feet from 
their bottoms; but if a lining of cast iron plates as before mention- 
ed, is used, the inside walls must be straight and perpendicular, or 
may have a slight and regular batter. 

The platform upon the arches must be as much wider than 
the intended water-course as will leave a towing path^ on one or 
both of its sides; and the usual manner of building aqueducts in 
brick or stone is to erect four parallel longitudinal walls upon it, 



OF CANAL LOCKS. 715 

of less thickness than above mentioned; the two inner walls being 
the sides of the water-course, and the two outer and thinner ones 
being flush or even with the face of the work, while the spaces 
between them are filled in with grouted rubble-work or beton, 
the top of which forms the towing paths. The two external 
walls are carried up as parapet walls, or they may be finished 
by a balustrade or railing for the safety and protection of the 
horses and passengers. When this mode of construction is adopt- 
ed, a large and solid mass of work of the full width of the towing 
paths, and of a height equal to the full depth of the water trough 
is necessary on each side, consuming much material and throw- 
ing great weight upon the piers; besides which there is often diffi- 
culty in discovering the position of and repairing leakages when 
they occur in the water trough. The writer therefore suggests 
that the two objects to be attained, which are eflfectual support 
to the trough walls, and elevated platforms for the towing paths, 
would be equally well obtained by dispensing with the two out- 
side walls and the rubble-work or beton, and running a series of 
arched vaults along the platform, the radius of the arches being 
nearly equal to the depth of the water trough. The spandrells 
of these arches may afterwards be filled in by the parapet walls, 
and the arches themselves being covered over with marl or any 
proper soil, will form the towing path, with much less weight, 
and expenditure of expensive material than in the other forms. 
The axis of these small arches being at right angles to the trough 
walls will give it effectual support, and as the arches need not be 
closed at their outer ends, they afford the means of examining 
and repairing nearly the whole of the trough walls at all times 
without digging up the towing path, or disturbing the regular 
traffic. 

1258. The above particulars, in addition to what has been 
stated in the body of the work, under the heads of Land Survey- 
ing, Levelling Earth-work, and construction in Masonry, Brick- 
work and Carpentry, it is presumed, when combined with some 
practice, will enable any one to survey a line for, set out and 
execute a canal, and with this we shall close our account of the 
operations of the Engineer. 

To those who are acquainted with the subject, it will be evi- 
dent that many objects of the Engineer's profession are passed 
without notice; and to such it will be equally certain that these 
objects could not be comprised in a single volume, however much 
it might be extended. The principles that we have endeavoured 
to establish and explain are general, and apply to constructions 
of every kind, and it is beheved comprehend a notice of all that 
generally falls under the direction and superintendence of a Civil 



716 INLAND NAVIGATION. 

Engineer in the general acceptation of the term. It was stated 
in the introductory chapter that the occupations of the Engineer 
are so various that no one man commonly applies himself to the 
whole of them, but selects that for which he has the greatest 
taste and liking, or which his particular connexion may throw in 
his way. Still none of these subordinate branches can be follow- 
ed with success without some portion of the knowledge which is 
attempted to be inculcated in the foregoing pages. To make use 
of even this information to advantage, a previous acquaintance 
with the general principles of natural philosophy is presumed, 
therefore no notice has been taken of the nature and operation 
of the mechanic powers, of the weight and elasticity of the 
atmosphere, and of the nature and etTects of hydrostatic pressure 
and hydraulic machinery. 

1259. In carrying on the operations which have been described, 
the Engineer may have occasion to construct pumps and other 
machines, and to plan or construct water wheels, windmills or 
steam engines, to obtain power to move them; and gearing or 
cogged wheels upon shafts to carry that motion and power from 
one place to another. All these involve the principles that have 
been laid down, such as the nature and strength of materials and 
the methods of building and framing them together; and when 
those principles are well understood, little difficulty can arise in 
planning the details. From the extent and variety of these ob- 
jects, any attempt at such a description of them as might prove 
useful is impossible, and the student must therefore refer for the 
particulars of their construction to works devoted to their particu- 
lar consideration, and among others Nicholson's Operative Me- 
chanic, Buchanan on Mill-work, Gray's Millwright's Assistant, 
Dr. Brewster's Edinburgh Encyclopedia, and the supplement to 
the fourth and fifth editions of the Encyclopaedia Britannica may 
be consulted with advantage. 



THE END. 



INDEX. 



PAGE 

Absolute strength of materials, 380 
how reduced from re- 
lative strength, - - 453 
Abstract book and abstracting dimen- 
sions, - - - 511 
Abutments for bridges, - 566, 612 
Adjustment of the levelling instrument, 157 
of the measuring chain, 106 
of the theodolite, - 130 
Adobi, or raw brick building, 502 
Air furnace for melting iron, &c. - 340 
Alabaster, - - - 250 
American bond for brick-work, - 485 
Angles, to measure, - 42, 122, 125 
to draw equal, - 52, 53 
to bisect, - - 54 
Angle of torsion, - - 427 
Annulus or ring, to find area of, - 92 
to find solid contents of, 98 
to find surface of, - 100 
Aqueducts in canals, - 713 
in brick and stone, - 713 
Arch, its origin, - - 635 
flowing, ... 584 
solid, in walls, - 586 
built on earth centres, - 587 
over bad foundations, - 613 
inverted, - - - 614 
counter, - - 586 
semicircular, used in architecture, 636 
elliptic, - - 640 
its advantages, - - 647 
gauged, camber, or scheme, 637 
Gothic, its varieties, - 638 
rough, - - - 638 
Arches of timber, examples of, 569 
Burr's principle of 
constructing, - - 575 
Arches, on the construction of - 634 
centring for building, - 581 
to set them out, - - 639 
of equilibration, - 643, 649 
catenarian, - - 642 
nomenclature of parts, 647 
on building them, - 648 
the theory of, - 649 
Arch moulds, ... 591 
Architect, his duties defined, - 15 
Archi volt of arches, - - 648 
Ashlar masonry, - - 464 
its disadvantages, - 465 
Astragal moulding, - - 69 
Axis of fracture, - - 430 



B. 

PAGE 

Back observations in levelling, 165 

Baltimore and Ohio Rail-road, - 689 

Balusters and balustrade, - 666, 667 

Band or fillet moulding, - - 69 

Banquette, in road making, - 229 

Bar iron described, - - 324 

Barking timber trees, - 209 

Base line for surveys, - - 107 

Basins or wet docks, - - 711 

Bath building stone, - - 252 

Battens, - - 307,549 

Battering plumb-rule, - 490 

walls, - - 489 

Battersea bridge near London, 565 

Bead moulding, - - 70 

Beam compasses, - - 46 

for steam-engine, trussed, - 557 

Beams, built, - - 553 

trussed, - • - 554 

rules for strength of, - 435 

when placed obliquely, - 442 

to support load at end, 445 

to obtain the strongest, out of a 

tree, - - - 452 

Bell metal, properties and composition, 365 

Bench marks in earth-work, - 196 

Beton cement, - - 294 

its composition, - 499 

Bevan, Mr., his experiment on nails and 

glue, - - - 418 
Bevil plumb-rule, - - 197 
Bird's-mouth joint, - - 629 
Birmingham Theatre roof, - 534 
Black lead pencils, - - 35 
Blackfriars bridge centring, - 604 
Blacksmith, his business and tools, 328 
Blasting rocks, - - 259 
Blenkinsop's first locomotive engine, 687 
Bludgett's timber bridge, - 571 
Boards defined and described, - 306 
for drawing upon, - 33 
Board measure, - - 314 
Bond, old English, Flemish, and Ameri- 
can, - - - 485 
Bond, vertical, for brick-work, - 487 
Bond timber in walls, - 494 
Boning a right line, - - 108 
Boring to try foundations, - 613 
Boulder stones, - - - 233 
for paving, - 243 
Box or flask castings, - - 343 
Brace, diagonal, - - 522 
Brass, general remarks upon, - 364 



718 



INDEX. 



Brazing or hard soldering, - 336 
Breast of a chimney, - - 548 
of earth-work, - 203 
Breaking of beams investigated, - 431 
Breeze used in brick-making, - 263 
Bricks described, - - 260 
ancient, - - 261 
their varieties, - - 273 
their size, - - 261 
mode of burning, - - 270 
Brick-earth, - - 262 
its preparation, - 264 
Brick-kilns, - - 270 
Brick arches, on building, - 634 
Bricklayer's level described, - 151 
Brick-work, - - - 483 
phraseology of, - 484 
Bridge of Blackfriars, - - 604 
ofCravant, - - 603 
of London, - - 597 
ofMenai, - - 668 
ofNeuilly - - 603 
of Orleans, - - 590 
Difficulties in its execution, - 664 
Bridge of Pont y ty Prydd, - 652 
of Westminster, - - 631 
Bridges of timber examined, - 562 
fine examples of, - 568 
Bridge, timber at Fairmount, Philadel- 
phia, - - - 569 
at Portsmouth, - 571 
at Trenton, N. J. 574 
at SchafThausen, - 573 
at Wittengen, - 572 
on roof principle, - - 566 
hanging or suspended, 567, 668 
its greatest load, - 575 
Bridges, swing and draw, - 576 
for canals, - - 694 
of iron, - - . 658 
Bridging and binding joists, - 548 
Building materials, - - 248 
acts of London and Boston, 371 
in Pise, - - 502 
arches, - - 661 
Burr's principle for timber arches, - 575 
Buttresses or counterforts, - 489 
flying, - - 491 



Cables, of iron chain, - - 410 

Caissoons for building in water, 630 

of bricks, attempted, - 633 

Calliper compasses, - - 335 

Cambering of beams, - " - 546 

Cambered arches, - - 637 

Camp paper, - - - 60 

Canals, lines, on setting out, - 144 

navigable, their advantages, 691 

their size, - - 684 

mode of construction, locks, 695 

bridges, - - 694 

Carpentry, - - - 516 

Carpenters' work, to measure> - 607 

Carts with three wheels, - - 207 

Carrara marble, - - 249 



Case hardening iron, 

Cast iron, - 

particulars of, 

trussed beams, 

swing bridges. 



364 
324 
337 
556 
580 



Castings, of iron, their four denomina- 
tions, - . - 340 
Castings, of iron, to calculate their 

weight, - - - 359 

Catenarian arch, - - 642 

Cavetto moulding, - - 69 

Cedar and Cypress timber, - 304 

Ceilings, their construction, - 546 

to complete their strength, 561 

Ceiling joists, - - - 546 

how fixed, - 547 

Cement, or hydraulic lime, - 288 

artificial, how prepared, 290 

Centre of a circle, to find, - 54 

Centring for brick or stone arches, 581 

formed of earth, - 587 

for small arches, - 588 

principles of its construction, 588 

mode of fixing and using, 583 

for bridge arches by Pilot, 593 

investigations of the strength of, 599 

mode of supporting, - 596 

by Perronet, - 603 

for stone bridge at Orleans, 590, 602 

new London bridge, - 597 

for Blackfriars bridge, 604 

for Waterloo bridge, - 606 

for Westminster bridge, 606 

for St. Peter's Church at 

Rome, . - - 592,598 

Chain for measuring land described, 104 

cables, of iron, - - 410 

its advantages, - 411 

cramps, and hoops, - 473 

Chair in rail-roads, - - 678 

their form, - - 689 

Chalk lime, - - 280 

Charcoal iron, ... 323 

Charred wood, its duration, - 375 

Chase in brick-work, - - 495 

Chimney stacks should be detached, 502 

Chimneys, precautions in building them, 371 

Chords, line of, • - 53 

Circle, to draw through three points, 54 

to find area of, - - 92 

Circular work in masonry, - 479 

in brick- work, - 493 

Circulating decimals, - 85 

Circunife renter, or surveying compass, 122 

Civil Engineer, origin of, - 20 

his duties, - 13 

Civil Engineers, Society of, - 19 

Clamp burning of bricks, - 273 

Clerk of works, his duties, - 18 

Coals, London method of unloading from 

vessels, ... 498 

Cock metal brass, - - 365 

Coffer-dams for building in water, - 623 

Cohesion of woods, - - 401 

of metals, -- - 403 

Coke for smelting iron, - 323 

oven, how formed, - - 323 

/ 



INDEX. 



719 



Cold short iron, - - 327 

shuts in iron, - - 329 

chisels, - - 332 

Collar beams, - - - 521 

Colours, and colouring drawings, 47 

Compasses or dividers, - - 40 

hair, - - 41 

folding, - - 44 

proportional, - 61 

beam, - - 46 

calliper, - - 335 

Compass, the surveying, - - 122 

Concrete, or Beton cement, - 294 

to make it, 499 

Conductors for lightning, - 377 

Cone, to find its solidity, - - 96 

its surface, - - 99 

Contraction of metals after casting, 355 

Contractors for earth-work, &c. - 189 

Construction or processes of building, 455 

Coping stones, - - 476 

Copper, sheet, for roofs, &c. - 365 

Copying drawings, - - 49 

by pricking, - 58 

by squares, 63 

Corbling described, - • 635 

Cores, for holes in castings, - 346 

for casting pipes, - - 347 

Corked cramps, - - 472 

Corking beams, - - 529 

Corrosive sublimate prevents rot, 375 

Cost of building several large bridges, 631 

Coved roofs, - - - 537 
Counter arches, 

Counterforts or buttresses, - 489 

Courses of masonry and brick-work, 459 

Crab for raisuig stones, - 258 

Cramps for uniting stone-work, 471 

brass, - - - 473 

corked, - - 472 

chain, - - r 473 

Crosby's builders' price book, - 482 

Cross multiplication, - - 74 

Cube, to find the solid contents of, 95 

Cupola for melting iron, - - 340 

Curb stones in paving, - 244 

Curves in rail-roads, - - 678 

how constructed and set out, 683 

may be contracted or diminished, 684 

Cymatium moulding, - 69 

Cyma re versa, or O G moulding, - 69 

D. 

Dams in rivers, - - 692 

Danger of ropes, - - 499 

Deal, English name for pine wood, 303 

Deals defined and described, - 306 

Decimal fractions, - - 83 

repeating - - 85 

Depth of beams important to strength, 436 

Diatonos or thorough stones, - 471 

Dies and taps for screw cutting, 332 

Dip of horizon, table of, - 148 

Dimension book for masonry, - 480 

for brick-work, 504 

for carpenters' work, 609 

Ditches for roads, - • 226 



Dividing lines, process of, - 52 
Docks for shipping, - 711 
Dotting nails in sheet lead, - 367 
Dovetailing, ... 542 
in stone-work, • 473 
Dovetail cramps, - - 472 
Do welled floors, - - 551 
cramps, - - 472 
Draining necessary to good roads, 225 
of foot-paths, - - 247 
pipes for side-walks, 247 
bricks, - . 276 
Drawbridges, - - 576 
Drawings, their requisites, - 26 
Drawing and drawing instruments, 27 
to scale, - - 30 
boards described, - 33 
paper, names and sizes of, 33 
pens of steel, - 39 
scales, - - 43 
problems useful in, 51 
Dredging machine, - - 631 
Drilling hard stones, - 259 
iron, - - - 332 
Drury Lane Theatre, apparatus for rais- 
ing building materials, - 497 
its roof described, 535 
Dry rot in timber described, how pre- 
vented, - - - 375 
Dry sand castings in iron, - 350 
Duodecimal arithmetic, - - 72 
Durability of materials, - 370 
instances of, - - 373 
of old London bridge, 563 

E. 

Earth-work or excavation, - 188 

mode of carrying on, - 202 

of measuring same, 1 98 

Echinus moulding, - - 69 

Eddystone light-house, how built, 473 

sketch of its history, - 474 

Edge rail-roads, - - 674 

Electricity, its effects on buildings, 377 

Elevation, drawing of, - 29 

Ellipse, to find the area of, - 93 

modes of drawing, - 640 

Engine and Engineer defined, - 9 

Embankments to form, - 200 

trimming of, - 201 

Emplecton or reticulated masonry, 471 

Estimating the price of cast iron, - 360 

Equilibration of arches, - 643,649 

Example of measuring masonry, - 480 

brick- work, 506 

Expansion of materials by heat, - 372 

Experiments on strength of materials, 385 

on morticing, - 552 

Extrados of an arch, - 647 



Faggotting WTOught iron, 327, 330 

Fairmount bridge, Philadelphia, 569 

Feather edged scales, - - 46 

boards, - 307 

Feathers or ribs in castings, what, 357 



720 



INDEX. 



Feathers, their importance, 
Feeders for navigable canals, 
Field book for land surveying, 

for levelling, 
Ferruginous sand-stone, - 
Fillet or band. 
Fine stuff or mortar. 
Fire, precautions to prevent its destruc- 
tion, ... 
Fire bricks, 

how to be used, 
Fishing beams, 
Flask or box castings, 
Flat joint brick-work, 
Flemish bond. 
Flawing arches, 

Flues and fire-places, their construction. 
Flying buttresses, 
Floors, their construction, 
folding, 
rebated, 

grooved and tongued, - 
dowelled, 

to construct with short timber, 
to compute strength of. 
Flooring boards. 
Folding compasses, 
Foot-paths, paved. 
Footing to walls. 
Force of compression, 
of tension, 
of torsion. 
Forging iron-work. 
Forms of beams to sustain loads. 
Forward observation in levelling, - 
Foundations, 

on made ground, 
on hills, 
on arches, 
on inverted arches, 
in coffer-dams, 
Foundation trenches, 

planked and timbered, 
deep and wet, 
Fractions, vulgar, 
decimal, 

to change one kind into an- 
other, . . - 
Framing timber, 
Framed buildings, 
truss, 
principals. 
Freemasonry, origin of. 
Free-stone, its varieties described. 
Fuel for burning bricks, 

for working wrought iron, 
Furnaces, how arched over, 

G. 

Galvanic effects on materials, 
Gallier's builders' price book. 
Gales, their construction, 

for canal locks. 
Gauge for size of wire, 

of slates and shingles, 
Gauged arches. 



448 
695 
136 
168 
252 
69 
465 

371 
275 
501 
540 
343 
501 
485 
584 
372 
491 
546 
549 
650 
550 
551 
557 
560 
549 
44 
246 
488 
389 
399 
422 
331 
446 
166 
612 
613 
614 
613 
614 
626 
613 
615 
621 
77 
83 

86 
516 
524 
526 
528 
457 
249 
272 
331 
587 



378 
482 
522 
523 
369 
531 
637 



Gauthey, M., his experiments on stone, 387 

Gib and key-joint for iron straps, 644 

Girders for floors, - - 546 

Girdling timber, - - 299 

Girt and quarter girt of timber, 309 

Glue and its power of adhesion, 420 

Globe or sphere, its surface, 100 

its solidity, 97 

Gothic arches, - - 638 

Gneiss, a kind of stone, - 254 

Granite, its advantages for paving, 242 

for building, - 252 

Gravel for road making, - 233 

Green or newly dug stone, - 251 

Green sand castings, - - 343 

Greenwich Hospital roof, *■ 633 

Grout and grouting brick-work, 499 

Grillage under foundations, - 620 

Grades and graduating rail-roads, 686 

Groove and tongue floors, - 650 

slip joints, - - 551 

Grubenmann's timber bridges, 572 

Grub-stone mortar, - - 294 

receipt for making it, 499 

Gun metal brass, - - 364 

Gunter's sliding rule, - 309 

Gutters, how formed in roofs, - 629 

Gutter, puddle, -. - 209 



H. 

Hacks for drying bricks. 

Hair compasses. 

Halving beams together. 

Headers in brick-work, - 

Heat, its effects on materials. 

Hemlock pine timber, 

Higgins, Dr., his treatise on mortar. 

Hilly ground, to survey, - 

Hipped roof. 

Hod for brick- work. 

Hoggin for puddling, &c. 

Hollow cylinders, their strength. 

Hooping beams with iron. 

Horizontal dip, table of, - 

Horse runs in earth-work. 

Hot short iron, 

Hupeau's centring for bridges. 

Hydraulic lime or cement, 

I&J. 

Inclined planes and ladders, 
on rail-roads, 
for canals. 
Instruments for dravi'ing, 
for surveying, 
for levelling. 
Ink, China or Indian, 
Intrados of an arch, 
Internal navigation. 
Inverted arches or inverts. 
Joggling beams together. 
Joiner and Joinery, 
Joining timbers together. 
Joists for floors and ceilings, 
manner of laying same, 
binding and bridging, 



265 
41 
639 
484 
371 
304 
284 
146 
630 
496 

208, 244 
449 
663 
148 
206 
327 

690, 602 
288 



496 
685 
712 

27 
119 
156 

35 
647 
691 
614 
451 
516 
539 
546 
547 
548 



INDEX. 



721 



Joists, to mortice, into girders, 
Iron, generally described, its ores, 
its combinations, 
crude or forge, . 
charcoal, . 
scrap, 

cast and wrought compared, 
bar, process of making, 
characters of good bar, 
chains, table of weights, 



551 
321 
322 
323 
323 
327 
324 
325 
327 
370 



chains, their advantage over ropes, 412 
ties and straps in carpentry, 
bridge at Colebrooke Dale, 

the Southwark, London, 

at Sunderland, 

of Telford and Douglass, 

for London, 
at Vauxhall, . 
Isodomum, or regular masonry, 
Jumping iron, 

K. 

Kiln for burning lime, . . 281 

for bricks, . . 270 

King post in framing, . . 526 

its joints and straps, 545 
Knee jointed masonry, 

Knobs in timber, . . 302 



541 

658 
660 
658 

659 
661 
470 
331 



Ladders, . . . 496 
Lagging, or covering for arch centres, 582 
Lancet pointed arch, . . 639 
Land surveying, . . 101 
operations, . . Ill 
Laps in sheet lead and copper, 366 
Lapping timbers, . . 539 
Lathe lor turning, . . 334 
Lead, sheet, and pipes, . 365 
Leather bands for machinery, . 417 
their strength, 418 
Level line defined, . . 150 
the bricklayer's, . 151 
the spirit, . . 153 
the flat plate, . . 155 
difference between real and ap- 
parent, . . 186 
Levelling instruments described, 156 
tlie water, 160 
the plumbet, 161 
process described, . 163 
its use, . 151 
simple and compound, . 167 
simple process, . 1?1 
staff and vane, . 162 
Lewis for raising stones, . 257 
Lightning rods, their use and construc- 
tion, . . . 377 
Lirae-stone and lime, . . 279 
chalk, . . 280 
stone-Urae, . 281 
shell, ... 286 
Lime-kilns and lime burning, . 281 
Line of chords, . 53 
and line-pins, . 487 

91 



Live oak timber, . . 304 

Liverpool and Manchester Rail-road, 687 

Load of timber, . . . 315 

the greatest on a bridge, 575 

Loam castings of iron, . . 350 

Loclis on navigable canals, . 695 

their distance apart, . 696 

mode of working them, 696 

on building same, . 698 

with inverted arch bottoms, 615 

side pound to save water, . 709 

Lock gates, . . 701 

Locomotive engines on rail-roads . 686 

much improved, 689 

of Blenkinsop, 687 

London bridge, ancient, . 562 

its numerous immense 

piers, . 563 

new, its centring, 597 

Lumber or timber, . . 305 



M. 

M roof, 

M' Adam's system of road making, 
Malm bricks or cutters, 
Marble described and its uses, 
Masonry or stone-work, . 

its varieties, 

of ancients. 

Free, Society, 

solid wrought, . 

rusticated, . 

ashlar. 
Mason, his business, . 
Mason's level, . 
Masts of ships, how constructed. 
Mastic or oil cement. 
Materials for building bridges. 
Maul, three handed, 
Measuring tapes. 



536 

234 
274 
249 
456 
459 
457 
457 
462 
463 
464 
457 
153 
451 
296 
657 
616 
199 



timber, general directions for, 308 

Gunter's scale applied to, 309 

fallacy of usual practice, 311 

standing timber, . 312 

excavation or earth-work, 198 

road-work, . • 245 

of masonry, . 47T 

of nibble stone- work, . 461 

of brick- work, . 503 
of carpenters' and joiners' 

work, . • 607 

book for masonry, . 480 

for brick- work, . 504 

Menai suspension bridge, . 668 

Mensuration, principles of, . 71 

problems in, . 89 

Metals, considered as building materials, 319 

Mica slate-stone, . . 254 

Mile stones or posts on roads, . 231 

Mill for making mortar, . . 295 

Millwright, his business, . 517 

Modulus of elasticity, . • 396 

of resiliance, . 398 

of cohesion, • . 401 

Mortar, its composition, ^^ . 278 

its constituent materials, 284 



722 



INDEX. 



Mortal-, proper mode of applying it, 499 

mills for preparing it, 295 

Mortice and tenon, . . 540 

the dovetail, . 541 

Morticing joints into girders, . 551 

Moscow, roof of Imperial Riding House, 537 

Mouldings, the several described, 68 

compound, . 70 

Moulding patterns for casting metals, 343 

Moulds lor circular brick-work, 493 

Mullions or Munnions, . 639 

N. 

Nails, experiments on their adhesion, 418 

Naked roofs and floors, . . 529 

Natural beds of stone to be preserved, 466 

Navigable canals, . . 691 
preliminary steps for 

forming, . 693 

Navigators or earth w"orkmen, 190 

Nicking out earth-work, . . 191 

O. 

Oak timber, . . .303 

Occupation bridges, . . 576 

Octagon, regular, to describe, . 55 

Offsets in surveying, how taken, 116 

round a pond or lake, . 117 

in brick-wOrk, , 488 

Offset staves, . . . 106 

O G or cyma reversa moulding, 69 

Oil paint, its use and advantage, 379 

Old men, in earth- work, . 196 

Old English brick bond, . . 485 

Oolite, or Bath building stone, 251 

Open sand castings, . . 340 

Ovolo moulding, . . 69 

Oven for burning coke, . . 323 

Ovens, how built, . . 587 



Painting in oil, its use, 

Palmer's single rail-road, 

Pannels in brick-work, 

Pantagraph, 

Paper for drawings, 

Parallel rulers, 

lines, to draw. 

Pargetting chimne}'s, 

Parker's, or Roman cement. 

Parr's ridge inclined plane. 

Paste, to make, (note,) 

Patterns to cast from, 

on making same, 346, 

Paving roads, 

granite the best material, 
process of performing. 

Perpendiculars, to raise, 

Perspective drawings, 

Petersburg and Roanoke Rail-road, 

Picket staves. 

Pickaxe, its proper form, 

Pig iron, 

Piers of bridges described, 

Piles, their use and forms. 



379 

679 
491 
64 
32 
37 
54 
372 
288 
689 
33 
342, 344 
355, 359 
240 
242 
243 
51 
28 
686 
107 
201 
337 
612 
6J6 



Piles, sheeting, , . 621 

removing after done with, . 630 

Piling foundations, . . 615 

Pile-driving machine, . . 616 

ofVauloue, 618 

how measured and valued, 

Pine timber, or deal, 

Pinning mortice joints, 

Pise buildings, . . i 

Pilot's principles of centring, 

his process for investigating their 
strength, 
Place bricks, 

Plans, first formation of, . 
Plain and pan-tiles, . 

work in masonry, . 
Plane table, 

Planks defined and described. 
Plaster of Paris, 

Platform for constructing centring, 
Plotting at survey, 
at levels, - 
Ploughed and tongued joints, . 
Plumb-rule, 

battering, 
bevil, 
Plumbet level, 
Plunger locks. 

Pointed style of architecture, 
Pointing old brick walls, 

flat and tuck, 
Pole plate in roofs. 
Polygons, 

to inscribe in circles, 
their use in arch centring, 590, 602 
Pont y ty Prydd bridge, . 652 

Portsmouth timber bridge, • 571 

Pot or cock metal, • . 365 

Pressure, its effects on materials, 383, 390 
Rennie's experiments on, 385 

Pressures in carpentry considered, 518 

practical rule for, . 393 

Price book for builders, . . 482 

Pricker for drawing, . . 42 

Prints in pattern making, • 347 

Problems in drawing, . 51 

in mensuration, • 89 

in land surveying, . 118 

Principals of a roof, . • 528 

Private and public roads, • 214 

Proportionals to find, . • 56 

Proportional compasses, • 61 

Proportions for strong beams, . 434 

Protractor, ... 42 

its use, . . 53 

Proving canal or level-work, . 182 

Pseudisodomum masonry, . 470 

Puddling to make earth water-tight, 208 
coffer-dams, . 625 

in making bar-iron, . 325 

Puddle gutter, . . 209 

Pug-mill for brick-earth, . • 267 

Pumping foundations, . 625, 628 

Punning earth-work, . • 200 

Purlins, ... 528 

Putlocks, . . .496 

Putty, a variety of mortar, . 465 



303 
542 
502 
598 



598 
274 
22 
277 
478 
119 
306 
293 
607 
114 
175 
551 
487 
490 
197 
161 
710 
638 
380 
501 
529 
93 
55,62 



INDEX. 



723 



Puzzolana cement, . . 292 

Pyramid, to find its surface, . 99 

its solidity, . . 96 

Q. 

Quartering, variety of scantling, . 307 

Quarter girt of timber, to take, 313 

table of, . . 319 

its result not correct, 311 

Quarrying stone, . . 255 

Queen posts, . . 532 

Quick sands, . . . 613 

Quincy granite, . . 253 



R. 



Racking back brick-work, . 493 
Rafters, common, . . 520 
principal, . . 528 
jack, . . . 530 
principal, to cut, . 528 
Rail-roads, their advantages, . 671 
their eeveral forms, 674 
of templates, . . 678 
edge rails, . 678 
of wrought iron, . 678 
Palmer's single, . 679 
best form for rails, . 681 
their graduation, . 686 
Raising building materials, . 496 
Rakes and ramps in brick-work, 492 
Rebate explained, rebated floor, . 550 
Reduced brick-work, . 512 
Reduction of levelling observations, 171 
Reed moulding, . . 70 
Reflecting surveyor's cross, . 110 
Relative strength of materials, 228 
Rennie, George, his experiments on pres- 
sure, . • . 385 
on tension, . 404 
Ribs for arch centring, . 583 
Ridge-piece in roofs, . . 528 
Right line, to set out, . 107 
Ring or annulus, to find area of, . 92 
solid contents of, 98 
Rivers, on rendering them navigable, 691 
Roads, to set out lines for, 144, 225 
their construction and qualifica- 
tions, . . 213 
their varieties, . . 214 
ancient, . • * 224 
early laws respecting, . 222 
in hilly countries, . 228 
their width and curves, . 230 
should not be watered, 246 
paved, . . 240 
summer and winter, . 245 
Road materials, . . 232 
making, the old system, . 233 
on M' Adam's plan, 234 
over bogs or morasses, 238 
Rod iron, . . . 324 
table of its weight, . 369 
Rollers for making bar iron, . 325 
best mode of casting ihem, 353 
Roman cement, . • 288 
roads, . . • 223 



Roofs, . . 527 

span, . . . 529 

hipped, . . 530 

tile, shingle, and slate, . 531 

directions for covering with metal, 366 
Roof of Greenwich Hospital . 533 

of Birmingham Theatre, . 534 

of Drury Lane Theatre, . 535 

of the Imperial Riding House, Mos- 
cow, . . . 537 
of Jefferson Medical College, 538 
for covering large ships, . 537 
oftlieMform, . . 536 
Ropes, their strength, . . 409 
materials used for making them, 412 
Captain Hud dart's patent, 414 
used for rail-road, inclined planes, 

416, 686 
Rotting, observations upon, . 373 

Round timber, to measure, . 309 

Rubble-stone described, . 249, 254 

masonry, . . 459 

Rules to determine resistance to pressure^ 393 



for size of shafts. 


427 


for strength of beams, 


435 


for same in oblique positions. 


442 


for same with loads at ends. 


445 


to reduce brick-work to standard, 512 


for framing timber, . 


522 


to compute strength of roofs. 


557 


the like for floors, 


560 


Rulers for drawing lines. 


36 


to try their goodness, 


37 


parallel, 


37 


Rusticated masonry, . 

S. 
Saddle back work, 


462 


477 


Safety dams on canals, 


695 


Sand, proper for mortar, . 


283 


Sand stones, 


251 


Sandy foundations. 


612 


Sap of timber. 


299 


Sawing and sav\yers. 


316 


Saws described and saw-mills, 


316 


Sawyer's work, to measure, 


316 


Scaffolding for building, . 


496 


Scales for drawing, . 


^9 


for levelling, 


175 


Scantlings of timber, . 


307 


to measure. 


315 


table of, . 


318 


Scarfing beams, . 


452 


how done, 


539 


Schnfl^hausen timber bridge. 


573 


Scheme arch. 


637 


Scoop tool, 


202 


Scotia moulding, 


69 


Scrap iron, . . . 


327 


Screws, how cut or made. 


332 


on their adhesion, 


418 


Seasoning of timber, . 


300 


Sectional drawings, 


31 


Section or profile, to plot. 


175 


how made more perfect, . 


179 


Segment of a circle, to draw, 


55 


Seppings, Sir Robert, his ship roofs, 


637 



724 



INDEX. 



Septarium, or cement stone, . 289 

Setting out canal or road lines, 144, 184, 193 

on hilly ground, 194 

Shafts to determine their strength, 227 

are stronger when liollow, 426 

Shear poles for raising stones, 468 

Sheet iron, . . . 324 

Sheeting piles, . . 621 

Shell lime, . ... 286 

Shifting bridges, . . 576 

Ship lapping beams, . . 539 

Shingle roots, . . 254 

Shingling and slating roofs, . 530 

Short timbers, to use in floors, 557 

Shovels for earth-work, . 201 

Shoulders in framing, . . 526 

Shrinking of timber, . . 373 

Shutting or welding iron, . 329 

Side pound locks for canals, . 708 

Sidings in rail-roads, . . 682 

Sienite or Boston granite, . 253 

Signal posts on rail-roads, . 682 

Simple and compound levelling, 167 

Skew backs of arches, . 648 
Slab-stone described, . 249, 253 

Slabs of timber, what, . 305 

Slaking lime, . . . 286 
Slates, their names, dimensions, and 

weights, . . . 531 
Slater, his business, . . 531 
Slating for roofs, . . 254 
Slide rule for timber measure, 309 
Slopes lor earth-work, . 192 
how set out and adjusted, . 198 
Smeaton's account of Eddystone Light- 
house, . . . 474 
Smith's forge and tools described, 328 
Soap stone, its properties, . 252 
Society of Civil Engineers, London, 19 
Sodding new made banks, . 212 
Soffit of arches, . . 647 
Soldering, hard and soft, . 335 
Solid arches in walls, . . 585 
Span roof, . . • 529 
Specific gravities, table of, . 454 
Specification of works, . 26 
Sphere or globe, to find its solidity, 97 
its convex surface, . 100 
Spirit level described, . . 153 
Splaying walls, . - . 492 
Springings of arches, . . 647 
Squares for drawing, . 39 
for copying drawings, . 63 
Square for earth-work, . 191 
Squaring dimensions, . . 71 
St. Peters's at Rome, its centring, 598 
Stages of wheeling in earth-work, 204 
Stakes for setting out work, . 190 
Steam-engines for rail-roads, . 687 
Steel, properties and manufacture of, 3G0 
blister, tilted or sheer, and cast, 361 
to harden and temper, . 362 
Stock bricks, . . 274 
Stone for building, . . 248 
Stone- work or masonry, . 456 
building, mode of ordering and re- 
ceiving, • . 458 
lime, . . 281 



Stone-work, rubble, . . 459 

solid wrought, . . 462 

ashlar, . . . 464 

how performed, . 467 

how measured, . 461, 477 

Stone sills to windows, . 476 

string courses, . . 476 

experiments on its hardness, 387 

quarries, . . . 255 

Straining piece and sill, . 533 

Straps or ties of iron for roofs, . 544 

best modes of fixing same, 545 

Strength of timbers, to determine, 557 

of materials, . 380 

to resist pressure, . 383 

of beams supported at both ends, 435 



of hollow cyllinders, 

of ropes, 

rules for, 

of leather bands, 

of nails, screws, and glue, 

relative reduced to absolute, 
Staff for levelling, 
Stiffness of materials, 
Stretchers in brick-work, . 
Striking centres of arches. 
Summer and winter roads. 
Sunk-work in masonry. 
Surveys, large, directions for, 

trigonometrical, 

on hilly ground, . 
Surveying cross, 

by reflection, . 
compress described, 
Surveyor of roads, his duties. 
Suspension bridges, . 
Swinging bridges, 

of cast iron. 
Sump in pumping, 
Switch in rail-roads, . 



T. 



449 
409 
415 
418 
418 
453 
162 
430 
484 
585 
245 
478 
134 
143 
147 
108 
110 
122 
217 
668 
578 
580 
629 
682 



75 



Table of aliquot parts of a foot, 

of difference in true and apparent 

level, . . 187 

of dip of the horizon . 148 

of inches in feet, . 76 

of sizes of drawing paper, . 33 

of land measure, . 103 

of specific gravities, . 454 

of cohesion of metals, . 403,404 
of woods, . 409 

of moduli of elasticity, . 398 

of length of scantling to cube foot, 318 
of quarter girt of round timber, 319 
of weights of flat, square, and 

round iron, . . 368 

of weights of crane chains, 370 

Tangents, to draw, . . 55 

Tapes for measuring work, . 199 

Taps and dies for cutting screws, . 332 
Target in levelling, . . 162 

Tarred ropes, . . . 415 

Tarrass, Dutch, . . 292 

Taylor's builders' price book, . 482 

Telescope sights, advantage of, 125 

Tempering steel, • • 362 



INDEX. 



725 



Templates for supporting beams, 

in iron foundry, 
Tenacity of metals, 
Tenders for performing work, 
Tenon and mortice, 

for principal rafters, 
best for joists, 
Tension, on the force of, 
Theodolite described, 
use of, . 
surveying by, . 
Theory of carpentry, 

of arches, 
Throating stone-work, 
Tide-work, 

locks for docks, 
Ties of iron for carpentry. 
Tiles for roofing and paving, 

directions for cutting, 
Timber defined, 

its varieties, . 
mode of seasoning, 
directions for measuring, 

cutting, . 
its denominations depend 

form, 
by the slide rule. 



on 



446 
343 
403 
180 
540 
542 
553 
399 
123 
128 
131 
518 
649 
476 
629 
712 
544 
276 
297 
296 
302 
300 
308 
297 

305 
309 



to find its height while standing, 312 
observations on its qualities, 408 
to compute its strength, 558 
Timber bridges, observations on, 562 
their simplest construc- 
tion, . . 564 
three principles of con- 
struction, . 568 
difficulties in ditto, 574 
Timber bridge over the Schuylkill, Pa. 569 
at Trenton, N. J. 574 
at Portsmouth, . 571 
Tin plates, their use, . 367 
Tinting or colouring drawings, . 47 
Tolls, how collected, . 218 
Toothing in brick-work, . . 495 
Torsion, on the force of; . 422 
Torus moulding, . . 69 
Tough bar iron, . . 327 
Tracing and tracing paper, . 59 
Tram-plate rail-roads, . 676 
Transferring paper, . . 60 
Transoms, . . . 639 
Trapezium, to draw, . .56 
Tredgold's experiments on pressure, 388 
Trenails, . . .539 
Trenton Bridge, New Jersey, . 574 
Triangle, to find area of, . . 91 
its importance in carpentry, 521 
Trigonometrical surveys, . .143 
Trimmers in floors, . . 548 
Trimming embankments, . 201 
Truss, in framing, . . 526 
Trussed girder of cast iron, . 556 
beam for steam-engine, 557 
Trussing timber beams, . 554 
T square for drawing, . . 39 
Tuck pointing brick-work, . 501 
Tunnels, . . 669 
Tumbling bays of canals, . 695 
Turning and turning lathe, . 334 



Turning platform in railways, . 682 

Turn-outs in railways, . 682 

Turnpike roads, . . 215 
how managed in England, 216 

Tye or tie in carpentry, . 519 

Tye beams, . . , 521 

V&U. 



Valleys of a roof. 
Valuation of timlDer, . 


530 
317 


of stone-work, . 


480 


of brick- work, 


514 


of carpenters' work, 
Vane for levelling, 
Vaniishing drawings, 
Vaults, 


607 

162 

48 

669 


Veneers described, 


308 


Vernier described, 


125 


Vertical bond, . 


487 


Vitruvius, his works. 


15 


Vouloue's pile engine, 
Voussoirs or arch stones, 


618 

647 


Vulgar fractions. 
Under-pinning walls. 


77 
516 



w. 

Walker's report on rail-road engine, 687 

Waterloo Bridge, London, . 586 

Water putty or fine stuff, • . 465 

Watering roads, detrimental, . 246 

Water tables of roads, . . 227 
Water levelling instrument, . - 160 

Weather boarding, . . 307 

Weathering stone-work, . 476 

Weirs, in river navigation, . 692 

Weight of cast iron, to calculate, 359 
of square, flat, and round iron, 368 

of iron chains, . 370 

Welding or shutting iron, . 329 

Wern wag's timber bridges, . 569 

Westminster Bridge, . . 606 

dimensions of, 631 

Wheelbarrows for earth-work, 203 

Wheeling planks, . . 203 
White smith, his business, . 328, 332 

Wholes and halves for drawing, . 61 

Wind, to guard against it, . 376 

Wind-bore of pumps, . . 629 

Wire and the wire gauge, . 369 

Wittengen timber bridge, . 572 

Woods, useful varieties of, . 302 

their comparative strength, 409 
Wooden bridges, their comparative value, 562 

construction of, . 564 

Wren, Sir Christopher, . 592 

Wrought iron-work, . . 328 



Yarns, rope, their strength, &c. . 413 

Yorkshire paving stone, . 254 

Young, Dr. Thomas, his observations on 

pressure, . . . 394 

Z. 

Zinc rolled, its use, . . 365 

protects copper from oiydation, 379 



ERRATA. 

Page 55, Art. 77, line 5, for radius q v, read q r. 

56, 83, last line, for EF : EG : : EH : EI, or AB : CD : : CD : EI, read 

EG : EF : : EI : EH, or CD : AB : : AB : EB. 

72, 122, line 14, for 83 feet, read 68 feet. 

91, ' 175, last line, for line x y, read x z. 

^'^, 198, line 6, after solidity, add the words, which multiply by the 

cube of one side. 
99, 200, 201, 202, and 203, to multiply for solidity the factor should be 

23, instead of 22. 
106, 223, line 18, for 7.2, read 7.92 inches. 

, 122, 259, line 4, for box d, read/. 

123, 262, line 4, for Fig. 74, read 77. 

124, 263, line 8, for (254), read (259). 
128, 269, line 6, for Fig. 47, read 74. 
152, 302, line 10, for 12, read 9. 

157, line 2, from top, for level i I, read ii. . 
" line 20, from top, for filling, read fitting. 

158, line 8, from top, for nut p, read R. 

' 160, line 27, from top, for pivot ^, read h. 
169, line 12, from bottom, for 200, read 220. 
171, last number in upper column of back sights should be 4.31. 
174, line 9, from top, for between c, read between i. 
178, line 25, from top, the 7i occurring twice in this line should be r. 

" line 12, from bottom, for line n^ read r. 
262, line 20, from top, for three and three-quarters, read two and three- 
quarters. 
304, Art. 545, line 7, for preservation, read preservative. 

596, line 22, from bottom, for adopt, read adapt. 

597, line 19, for position, read positions. 

600, line 16, for deducing, read reducing. 

601, line 8, from bottom, for number, read member. 
603, Art. 1088, line 1, for Cravaut, read Cravart. 

606, line 5, from bottom, for Lubelye, read Labelye. 

607, to end of line 23, from bottom, add the word the. 
614, line 8, from bottom, for line e c, readc c. 

620, Art. 1119, line 14, for distinct, read distant. 
623, 1123, line 14, for pier, read piers. 

628, line 5, from bottom, for prominent, read permanent. 

629, Art. 1132, line 7, for as earth, read no earth. 

715, 1258, line 3, insert a comma after the word Levelling. 



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